Theoretical Physics | Physical Research Laboratory

2026

Detecting Dark Matter with Planets and Stars

Date: 2026-02-12
Speaker: Dr. Anupam Ray
Venue: Theory seminar room no: 469

Abstract

In this talk, I will discuss how planets and stars can be utilized as novel and powerful detectors of dark matter. I will begin with planets, focusing on how our own Earth can efficiently probe a rare species of dark matter (dark matter sub-components) with a very short collision length, for which conventional underground direct-detection experiments lose sensitivity. I will then turn to stars, highlighting how nuclear transitions in stellar interiors can give rise to ultralight axions, opening distinctive observational windows. Taken together, these examples demonstrate how planetary and stellar environments offer complementary and cost-effective avenues to search for dark matter, extending sensitivity into regions of parameter space that remain largely inaccessible otherwise.

Chasing Dark Matter: From Light to Heavy

Date: 2026-02-11
Speaker: Dr. Anupam Ray
Venue: Theory seminar room no: 469

Abstract

The nature of dark matter remains one of the key problems in modern physics, as its mass and interaction strengths are uncertain across an enormous range of scales. In this talk, I will present a scale-agnostic perspective and survey strategies to search for dark matter across the full mass spectrum, from ultralight to the heaviest candidates. I will emphasize how ideas and techniques from astrophysics, particle physics, and nuclear physics together can provide a powerful and unified framework for unraveling this mystery. By weaving together insights from these traditionally distinct approaches, I will argue that meaningful progress on dark matter will emerge from the interplay of ideas across traditional boundaries.

An implementation of GKZ hypergeometric series of Feynman integrals inside ‘Regions’

Date: 2026-02-06
Speaker: Dr. Ratan Sarkar
Venue: ONLINE

Abstract

We present an implementation of Gel’fand–Kapranov–Zelevinsky (GKZ) hypergeometric series for Feynman integrals within the Method of Regions (MoR). Our approach establishes a direct link between the geometry of Newton polytopes and the analytic asymptotic expansion of Feynman integrals in D dimension. By embedding GKZ solutions associated with distinct regions, we construct an automated framework that identifies contributing sectors, generates the corresponding GKZ-series solutions, and performs their systematic expansion in the dimension regulator. We have developed a Mathematica package, GKZRegions, which can be used to derive boundary conditions for differential equations of master integrals and to evaluate region contributions in effective field theories such as SCET.

Superconducting order parameter manifested by Quasicrystal

Date: 2026-01-20
Speaker: Dr. Sougata Biswas
Venue: Theory Seminar Room no 469

Abstract

Recent discovery of the superconducting ground state in quasicrystals (QCs) has opened up an exciting new avenue for superconductivity based on QCs. In this work, we explore the scope by theoretically investigating the behavior of the superconducting order parameter (OP) in various QCs based on the attractive Hubbard model. By systematically analyzing models generated through various growth rules, we elucidate the influence of aperiodicity on the OP amplitudes and how it evolves towards the periodic limit with the change in the structural pattern. We study the evolution of the OP with respect to the temperature, strength of the interaction, and nearest-neighbor hopping amplitude. Our numerical analysis identifies the most favorable QCs and parameter regime that support enhanced onsite pairing amplitudes. Additionally, we provide a comparative analysis of the superconducting transition temperatures across the range of aperiodic configurations. To gain further insight into these systems, we compute thermodynamic quantities which enable us to determine which QCs are most conducive to Cooper pair formation.

THE QUANTUM HALL EFFECT: APPLIED SCIENCE’S GIFT TO FUNDAMENTAL SCIENCE

Date: 2026-01-02
Speaker: Prof. Ravindra N. Bhatt
Venue: Thoery seminar room no: 469

Abstract

The discoveries of the integer and fractional quantum Hall effect (IQHE/FQHE) in a two-dimensional system of electrons in 1980-82 gave rise to the field of topological matter. These discoveries brought about a revolution in our understanding of the physics of condensed matter and resulted in six scientists winning the Nobel Prize in Physics. Since the original discovery, the two-dimensional electron system subjected to a large perpendicular magnetic field has become a veritable goldmine for the condensed matter physicist. Completely unexpected and exotic phenomena such as fractionalization of electronic charge, composite particles, Abelian and non-Abelian quantum states, and topological phases have entered the lexicon of quantum condensed matter. In addition, the system has provided examples of previously known phenomena such as topological spin excitations and charge density wave phases, the latter coming in several incarnations such as electron crystals, bubble crystals, and striped phases. Behind this amazing discovery lies the story of painstaking development of semiconductor heterostructures, a field motivated in large part by its technological importance. This was but one in a series of success stories involving the vast field of semiconductor technology, starting with the original discovery of the transistor by physicists at Bell Laboratories in 1947. Without these developments in applied research, the IQHE and FQHE would scarcely have been discovered, and our understanding of the richness of nature would have been that much poorer. This talk will trace this interplay of science and technology in the context of semiconductor heterostructures, culminating in the discovery of the FQHE, and unfolding of its complex, hierarchical structure. Following that, I will give an overview of the fascinating phenomena that QHE exemplifies. Finally, I will briefly discuss a couple of examples from the past decade that my group has been involved in, using a combination of analytical and state-of-the-art computational techniques. One will examine a phase in detail, and another the promise of new material platforms.

Simulation-Based Inference

Date: 2026-01-01
Speaker: Dr. Jay Sandesara
Venue: Theory seminar room no: 469

Abstract

Many modern experiments produce extremely high-dimensional data, while relying on complex simulations for their statistical modeling. In such settings, the likelihood is often not available in closed form. Simulation-Based Inference (SBI) is a family of emerging techniques that allow statistical inference on parameters of the statistical model directly using high-dimensional data, even when the likelihoods are not analytically tractable. This is done by leveraging deep-learning techniques to directly build likelihood-based or posterior-based inference models without any intermediate steps that lose information. These methods can be significantly more powerful than traditional approaches that first compress high-dimensional data into low-dimensional summary observable and then build approximate likelihoods as a function of the summary observable. Such compression can reduce sensitivity by discarding how the high-dimensional information varies as a function of the model parameters. In this talk, I will review the basics of SBI, focusing primarily on applications in ATLAS and CMS analyses at the Large Hadron Collider (LHC), and briefly highlighting applications in other domains. I will also introduce novel developments that allow for scalable inference when the likelihood model depends on hundreds of nuisance parameters describing systematic uncertainties, as is typical in LHC analysis. These developments resulted in first-ever measurements at the LHC using SBI [1, 2]. 1. Measurement of off-shell Higgs boson production in the H->ZZ->4l decay channel using a neural simulation-based inference technique in 13 TeV pp collisions with the ATLAS detector 2. An implementation of neural simulation-based inference for parameter estimation in ATLAS

2025

Interpretable Jet Physics Beyond IRC-Safety

Date: 2025-12-24
Speaker: Deepanshu Srivastava
Venue: Theory seminar room no: 469

Abstract

Deep (machine) learning methods for jet classification increasingly incorporate theoretical structure from QCD (Quantum Chromodynamics), leading to models that are not only performant but also interpretable. Previously, we have demonstrated that embedding infrared and collinear (IRC) safety and geometric equivariance into graph neural network architectures yields a stable and analytically meaningful representation for quark-gluon discrimination. However, extending these principles to a more complex task - such as boosted top-quak identification poses new challenges. Top tagging observables probe multi-prong substructure and often rely on quantities that are not strictly IRC-safe  but instead fall into the broader class of Sudakov-safe. In this seminar, I will present the results from applying equivariant and IRC-safe feature extraction techniques to top classification, highlighting both the successes and limitations when moving beyond the IRC-safe regime. Motivated by these observations, we will outline a framework for constructing Sudakov-safe neural networks, designed to remain robust in a region of phase space where IRC-safety alone is insufficient. By incorporating physics-motivated constraints, such networks offer a principles path towards reliable deep learning models for multi-scale jet substructure tasks, helping to bridge the gap between theory-aware machine learning and collider phenomenology.

Tailoring topological superconductivity, Bogoliubov Fermi surfaces and superconducting diode effect through the thread of unconventional p-wave magnets

Date: 2025-12-18
Speaker: Amartya Pal
Venue: Theory seminar room no: 469

Abstract

The recently discovered unconventional momentum-dependent magnetic orders have broadened our understanding of magnetism beyond conventional ferromagnetism and antiferromagnetism. Among them, p-wave magnets (pWMs) constitute a novel class of odd-parity non-collinear compensated magnetic orders leading to spin-split energy bands. In this work, we establish pWMs as fertile ground to realise three major superconductivity-driven quantum phases, topological superconductors (TSCs), Bogoliubov Fermi surfaces (BFSs), and the superconducting diodes which emerge within a single unified framework. Implementing a minimal microscopic model that combines p-wave magnetic order, exchange coupling, an external Zeeman field, and many-body interactions, we propose the emergence of a rich set of exotic phases utilizing the fully self-consistent mean-field formalism. These include conventional Bardeen–Cooper–Schrieffer (BCS) pairing as well as unconventional finite-momentum Fulde–Ferrell (FF) and Larkin–Ovchinnikov (LO) pairing states. Moreover, even without Rashba spin–orbit coupling and external magnetic fields, pWMs can undergo a transition to a topological superconducting phase anchoring Majorana flat edge modes, a hallmark of two-dimensional TSCs. With a Zeeman field, the system develops BFSs in the gapless LO and FF phases, characterized by a finite zero-energy quasiparticle density of states. Finally, we show that the superconducting diode effect appears naturally in the asymmetric FF state, which is quantified by the diode efficiency. Therefore, our study establishes pWMs as a versatile platform for realising band topology, unconventional superconductivity, and non-reciprocal transport in a single framework.

High mobility half-metallic interface state in CrI3/WTe2 based heterostructures

Date: 2025-12-11
Speaker: Dr. Nivedita Pandey
Venue: ONLINE

Abstract

CrI3 and its heterostructures are particularly advantageous due to their intrinsic two-dimensional magnetism, stacking dependent magnetism, high spin polarization, and ability to form van der Waals interfaces, making them a good candidate for exploring spin-dependent transport phenomena. In this work, we designed a robust half-metallic interface state in the CrI3/WTe2 van der Waals (vdW) heterostructure considering 2H and 1T’ phase of WTe2 exhibiting 100% spin polarization and an extraordinary magnetoresistance exceeding 109 %. The CrI3/2H-WTe2 configuration emerged as an exceptional candidate for applications in data storage, and spintronics. By designing a device incorporating CrO2 electrodes, we model charge and spin transport in this heterostructure and analyze thermal properties under parallel (PM) and antiparallel (APM) magnetization states. Using Density Functional Theory (DFT) and Non-Equilibrium Green’s Function (NEGF) methods, we explore how variations in temperature between CrO2 electrodes impact spin-polarized currents and demonstrate nearly perfect spin-filtration efficiency at low temperatures across both the 1T ′ and 2H phases of WTe2. The device also shows high thermal magnetoresistance (MR), further enhancing its applicability for spin-caloritronic functions. Transmission spectra for PM and APM states reveal temperature-dependent spin transport, reinforcing the heterostructure’s spin filtering effectiveness. This study represents the first detailed investigation of a heterostructure device with CrI3 and WTe2 phases and CrO2 electrodes, highlighting the superior spin-filtration and MR capabilities of the CrI3/2H-WTe2 interface. The robust half-metallic state and remarkable spin-filtering efficiency underscore the potential of this structure for developing advanced thermally controlled spintronic and spin-caloritronic devices. References: 1. Ding, X. et al., “Spin caloritronics in two-dimensional CrI3/NiCl2 van der Waals heterostructures. Phys. Rev. B, 103, 115415, 2021. 2. Pandey, N. et al., “Robust high mobility half-metallic interface state in CrI3/WTe2 based heterostructures,” ACS Applied Materials & Interfaces 17, 51448, 2025.

Decoding the Mystery of Dark Matter with Celestial Objects

Date: 2025-12-10
Speaker: Dr. Anupam Roy
Venue: ONLINE

Abstract

Dark Matter (DM), which constitutes a major portion of our Universe, remains mysterious. Despite decades of experimental and theoretical efforts, its microscopic identity is still unknown to us. In this talk, I will walk you through how a variety of celestial objects can be utilised as powerful DM detectors. This astrophysical probe, complementary to the terrestrial and cosmological probes, covers a significant portion of the DM parameters (DM mass and its interaction strength with nucleons) which otherwise remains elusive. In particular, I will discuss how EM and GW observation of compact stars can act as leading probes for particle DM interactions and more importantly, hold significant discovery potential.

Hidden Tracks: Reconstructing the scientific journey of Marietta Blau and Bibha Chowdhuri

Date: 2025-12-08
Speaker: Prof. Srubabati Goswami
Venue: Theory seminar room no: 469 (offline + online)

Abstract

Marietta Blau was born in Austria, and Bibha Chowdhuri in India. The common thread that binds them is their passion for science and their pathbreaking contributions in cosmic ray research. However, despite their remarkable contributions, both the scientists remained largely unrecognised and marginalized. This talk will trace their journey and recount their contributions, including Blau’s development and refinement of the nuclear-emulsion technique and her discovery of disintegration stars, Chowdhuri’s early identification of meson-like events in the Himalayas, her work on extensive air showers, and her later contributions to deep-underground muon experiments in India. Their stories reflect on overlooked histories and serve as a reminder of perseverance, ingenuity, and dedication despite the odds with the hope that it will inspire all, especially women, to pursue the challenges of research in science. Note : This talk is part of the series "PAVINARI" organized by the Gender in Physics Working Group of Indian Physics Association

How does aperiodicity affect behaviors of binary systems?

Date: 2025-12-02
Speaker: Achintyaa
Venue: THEORY SEMINAR ROOM NO: 469

Abstract

Aperiodic systems lack translational symmetry but may posses some ordering over different ranges and can be classified based on the range of order present. We consider a one-dimensional Fibonacci chain as a model aperiodic binary system within the tight-binding framework. I will show how aperiodicity fundamentally modifies electronic properties like the energy band structure, density of states, and behaviour of the wave functions, compared to its periodic counterpart.

Strong CP violation in dense matter : Consequences for neutron stars

Date: 2025-11-28
Speaker: Prof. Hiranmaya Mishra
Venue: THEORY SEMINAR ROOM NO: 469

Abstract

We investigate the effects of including strong CP violating effects through axion fields in the microscopic equation of state of massive hybrid neutron stars. We assume that their cores contain deconfined quark matter and include the effects of axions via an effective‘t Hooft determinant interaction. The hadronic crusts are described using different approaches in order to make our results more general. We find that the presence of axions stabilizes massive hybrid neutron stars against gravitational collapse by weakening the deconfinement phase transition and bringing it to lower densities. This enables to reproduce hybrid neutron stars in agreement with modern astrophysical constraints.

Coexistence of electron and phonon topology in pyrite type semimetals

Date: 2025-11-27
Speaker: Prof. G. S. Vaitheeswaran
Venue: Theory seminar room no: 469

Abstract

Over the past two decades, the pursuit of novel topological phases of matter has become a major focus in condensed matter research. Beyond Dirac and Weyl particles, a variety of unique quasiparticles, distinct from those studied in high- energy physics, have attracted significant attention. This study explores multi- fold degenerate fermions beyond Dirac and Weyl types in pyrite-structured SiX₂ compounds, where X = P or As. Through symmetry analysis, we uncover the topological features of multi-fold fermions with four-fold and six-fold degeneracies located at the Γ and R points of the Brillouin zone. These nodes, protected by crystalline symmetries, present an excellent platform for investigating novel topological properties and the physical phenomena associated with them. Additionally, these compounds exhibit intriguing topological features in their phonon dispersions. Specifically, we identify the coexistence of three nodal surfaces (NSs) and a phononic Dirac nodal-line (DNL) network. This DNL network consists of three intersecting nodal lines, each residing in a distinct momentum plane (kx, ky, kz) and converging at a common nodal point. Such a configuration is extraordinarily rare in phononic systems, creating opportunities for experimental validation through observable phononic surface states. These findings establish SiX₂ compounds as a promising platform for studying multi-fold fermions and their potential applications. Moreover, the discovered phononic topologies highlight these materials as exceptional candidates for investigating novel bosonic excitations, advancing the understanding of topological phenomena in solid-state systems.

Quasiclassical electron transport in topological Weyl semimetals

Date: 2025-11-20
Speaker: Azaz Ahmad
Venue: online link: https://imeet.vconsol.com/join/8617443886?be_auth=MDk0MzY2

Abstract

Weyl fermions bridge geometry, topology, and physics, appearing as excitations in Weyl semimetals (WSMs) with unique electronic properties. This seminar will explore chiral anomaly (CA) in WSMs, primarily through longitudinal magnetoconductance (LMC) and the planar Hall effect (PHE). While intervalley scattering is known to reverse LMC, we identify a new mechanism: a smooth lattice cutoff induces nonlinear effects leading to negative LMC. Using a tilted Weyl fermion model, we map phase diagrams to diagnose CA signatures [1]. Strain, acting as an axial magnetic field, introduces a ‘strong sign-reversal’ in LMC, distinct from external fields requiring intervalley scattering. The interplay of external and chiral gauge fields enriches LMC phase diagrams, and we predict distinct strain-induced features in PHE [2]. Extending to nonlinear transport, we develop a theory for the chiral anomaly-induced nonlinear Hall effect (CNLHE), revealing nonmonotonic conductivity in WSMs and a contrasting quadratic dependence in spin-orbit coupled metals [3]. Finally, we generalize CA to pseudospin-1 fermions, showing distinct transport signatures and enhanced sensitivity to internode scattering [4]. These findings provide a unified framework for diagnosing chiral anomaly in diverse chiral quasiparticles, guiding future experimental studies.

Monte Carlo Sampling for Wave Functions Requiring (Anti)Symmetrization

Date: 2025-11-18
Speaker: Dr. Ajit C. Balram
Venue: Theory seminar room no: 469

Abstract

"Many strongly correlated states, such as those arising in the fractional quantum Hall effect and spin liquids, are described by wave functions obtained by dividing particles into multiple clusters, constructing a readily evaluable wave function in each cluster, and (anti)symmetrizing across these clusters. We introduce a method to compute quantities such as energies and correlators, using Monte Carlo simulations for these states. Our framework overcomes the factorial scaling of explicit (anti)symmetrization, allowing for studies of systems beyond the reach of exact diagonalization.References: [1]. A. Ahmad et al., Phys. Rev. B 103, 115146 (2021). [2]. A. Ahmad et al., Phys. Rev. B 107, 144206 (2023). [3]. A. Ahmad et al., Phys. Rev. B 111, 035138 (2025). [4]. A. Ahmad et al., Phys. Rev. B 112, 045135 (2025). "

Supercurrent detection of Majorana-mediated quantum-phase transitions

Date: 2025-11-13
Speaker: Dr. Debika Debnath, PRL
Venue: Theory seminar room no 469

Abstract

"We study the experimental signatures of the quantum phase transition (QPT) through the supercurrent probed via scanning tunneling microscopy (STM) to a spin-polarized adatomic impurity which is embedded on a superconductor, giving rise to the non-degenerate Yu-Shiba-Rushinov (YSR) state. We consider the YSR as a controllable state by the adatom's rotational angles ($zeta, heta$) and the adatom is coupled to the two end-mode Majoranas. Recent work by Awoga et. al. [1] has shown that controlling the coupling between the YSR and Majorana states through the adatom rotation, can change the parity of the quantum states by modifying the effective ground state energies of both the YSR and Majoranas, which leads to QPT. However, high-precision measurements are elusive for the predictions of the QPT points. Therefore, in this work, we calculate the supercurrent through the YSR-Majorana coupled state and find the jump in the supercurrent at the topological QPT points (i.e. the critical YSR-Majorana coupling strengths), which establishes the supercurrent as an experimental signature of the QPT in our model superconducting junction. We have also investigated the effects of the strong tunnelling and finite temperature on the QPT via the supercurrent calculation. In addition, our result shows that control over the Shiba energy may induce a '0-pi' phase transition to the topological supercurrent. References: [1] F. Pientka, L. Glazman and F. Von Oppen, Phys. Rev. B 88, 155420 (2013). [2] O. A. Awoga, I. Ioannidis, A. Mishra, M. Leijnse, M. Trif, and T. Posske, Phys. Rev. Res. 6, 033154 (2024)."

Different Ways to Calculate NLP Amplitudes of Scattering Processes

Date: 2025-11-11
Speaker: Shuvendu Roy, PRL
Venue: Theory seminar room no: 469

Abstract

The scattering cross-section serves as a bridge between theoretical predictions and experimental observations. However, from a theoretical perspective, the perturbative expansion of the scattering cross-section may break down near the threshold region of certain kinematic variables. To preserve its perturbative behaviour, resummation techniques are employed. There exists a complete resummation theory for LP terms, but not yet for NLP terms. Two approaches are available to compute NLP leading logarithms: the first extends the methods used for colour-singlet production, but this makes the calculation more complex. To avoid these complications, a new technique has been proposed based on the spinor-helicity formalism with shifted spinors. Its application to H + jet production will be reviewed in the discussion, with a short introduction to the previous method along with its disadvantages.

Neutrino oscillations in the plane wave and wave packet formulations

Date: 2025-11-04
Speaker: Safana P Shaji
Venue: Theory seminar room no: 469

Abstract

Starting with the theoretical development of neutrino oscillations from plane wave to wave packet formulation, the talk aims to provide insight into the quantity of decoherence, which outlines the wave packet separation. The comparison of oscillated and decohered events is carried out through the lens of Jiangmen Underground Neutrino Observatory (JUNO) experiment, within which we delve into the mass hierarchy and theta12 sensibilities.

Search for dark matter over a wide mass range: using JWST and neutrino telescopes to search for non-gravitational signatures of dark matter

Date: 2025-10-10
Speaker: Dr. Ranjan Laha
Venue: Theory seminar room no: 469

Abstract

"I will discuss two different ways to search for dark matter (DM). First, I will discuss how we used JWST data to probe eV-scale QCD axion DM or axion-like particle (ALP) DM decaying into two photons. This will produce a distinct line signature in the spectroscopic observations made by JWST. Using the latest NIRSpec IFU spectroscopic observations from JWST, we put some of the strongest bound on the photon coupling for QCD axion/ ALP DM in the mass range between 0.47 and 2.55 eV. In the second part of my talk, I will discuss how neutrino telescopes like IceCube and Super-Kamiokande can probe DM - electron scattering. DM can get captured inside the Sun due to DM - electron scattering and it can annihilate into neutrinos and anti-neutrinos. Using latest neutrino measurements, we set world leading limit on DM - electron scattering for DM masses between 10 GeV to about 10^5 GeV."

Improved Constraints on Coexisting WIMP/ FIMP Dark Matter and Primordial Black Holes

Date: 2025-10-06
Speaker: Dr. Prolay Krishna Chanda
Venue: Theory seminar room no: 469

Abstract

Particle dark matter and primordial black holes (PBHs) may coexist with significant cosmic abundances, each contributing to the observed dark matter density ΩDM. Large populations of PBHs with ΩPBH ∼ ΩDM are strongly constrained for masses above 10−11M⊙. If the WIMP/ FIMP particle dark matter has interactions with the Standard Model, new constraints arise due to pair-annihilations that are enhanced by the PBHs, resulting in dark matter indirect detection constraints on fPBH — these bounds rule out the mixed WIMP-PBH dark matter for velocityindependent cross-section, ⟨σv⟩ ∼ 10−26cm3/s. In this talk, we will discuss how a particle DM candidate with a velocity-dependent cross-section relaxes these bounds. We also derive the bounds on mixed scenarios in which PBHs coexist with particle dark matter whose relic abundance is set via freeze-in (‘FIMPs’). We show that while the restrictions on fPBH are less constraining for FIMPs than WIMPs, modest bounds still arise for large classes of models.

Stable and Interpretable Jet Physics with IRC-Safe Equivariant Feature Extraction

Date: 2025-09-25
Speaker: Deepanshu Srivastava, PRL
Venue: Theory seminar room no: 469

Abstract

"Deep (machine) learning has achieved remarkable success in the complex area of QCD (Quantum Chromodynamics) jet classification using low-level calorimeter data from high-energy physics detectors. However, a significant challenge persists: understanding what these models learn and how their features correlate with established QCD observables. Improving interpretability is essential for building robust and trustworthy machine learning tools in any of their applications. To tackle this challenge, we present a case study using graph neural networks for quark–gluon discrimination, systematically incorporating physics-motivated inductive biases. In particular, we design message-passing architectures that enforce infrared and collinear (IRC) safety, as well as additional symmetries, including E(2) and O(2) equivariance in the rapidity–azimuth plane. Using simulated jet datasets, we compare these networks to unconstrained baselines in terms of classification performance, robustness to soft emissions, and internal feature organisation. Our findings demonstrate that embedding symmetry and safety constraints not only improve robustness but also ground network representations in established QCD structures, providing a principled path toward interpretable deep learning in collider physics. "

Amplifying muon-to-positron conversion in nuclei with ultralight scalar dark matter

Date: 2025-09-22
Speaker: Dr. Purushottam Sahu
Venue: Theory seminar room no: 469

Abstract

"I will present an analysis of the lepton-number and lepton-flavour-violating process of muon-topositron conversion µ − +N → e + +N ′ , in the presence of an ultralight scalar dark matter (ULSDM) field which couples to neutrinos. The ULSDM contributes to the effective off-diagonal Majorana mass mµe, therefore amplifying the rate of muon-to-positron conversion to experimentally observable levels. Using existing bounds from SINDRUM II, COMET, and Mu2e experiments, we derive constraints on the flavour-off-diagonal couplings of neutrinos to ULSDM . Our work reveals that upcoming experiments can provide stronger sensitivity to these new couplings than bounds arising from cosmological surveys and terrestrial experiments.

Looking under the lamppost for dark neutrino masses

Date: 2025-09-18
Speaker: Dr. Manibrata Sen
Venue: Theory seminar room no: 469

Abstract

The origin of neutrino masses remains one of the most pressing open questions in particle physics. While conventional approaches rely on extending the Standard Model with heavy fields or new symmetries, an alternative idea has recently emerged: neutrino masses may arise through refraction in the background of ultralight dark matter. In this framework, neutrinos acquire dynamic, effective, time-varying masses as they propagate through a coherent oscillating field, leading to distinctive imprints on oscillation experiments, beta-decay searches, and astrophysical neutrino signals. In this talk, I will introduce the basic mechanism of refractive neutrino masses and discuss its phenomenological consequences for laboratory, astrophysical, and cosmological probes and highlight how upcoming experiments may provide the first opportunities to test this novel connection between neutrinos and the dark sector.

New plasmon-like mode in PdTe2: Raman scattering and memory function study

Date: 2025-08-26
Speaker: Dr. Bharathi Ganesh D, PRL
Venue: THEPH Room no: 469 (seminar room)

Abstract

PdTe2 is a 2D material with its bands having a tilted Dirac cone structure. Due to its novel band structure it is touted to have many promising applications. Understanding the low energy excitation of such materials is important and in this direction we reported a new plasmon-like mode emerging at low temperatures (< 100 K) in PdTe2. We support this claim with a phenomenological analysis based on the memory function formalism.

Quantum mechanics, decoherence, and quantum-to-classical transition

Date: 2025-08-14
Speaker: Prof. Navinder Singh, PRL
Venue: Room no: 469 (Main Campus)

Abstract

This talk is divided into two parts: First part will be an elementary introduction to the theory of decoherence, quantum mechanics, and quantum-to-classical transition. We will discuss how Niels Bohr's idea of the "cut" and the requirement of a classical apparatus for the interpretation of quantum mechanics can be rationalized in the framework of the modern theory of decoherence by Zurek and others. In the second part, we present our results related to the Ovchinnikov-Erikhman theory of decoherence. We point out the problems with this scenario and revise it to apply it to a realistic case of the motion of conduction electrons. Interesting results are obtained. Our results agree with the alternative master equation approach.

Probing Compressed Inert Scalars with Forward Muon Tagging at the Muon Collider

Date: 2025-08-05
Speaker: Dr. Chandrima Sen, PRL
Venue: Room no: 469 (Main Campus)

Abstract

The compressed mass spectrum of the Inert Doublet Model (IDM) poses a significant challenge for current collider experiments, as the soft visible decay products and suppressed production rates hinder conventional search strategies. In this talk, I will explore the discovery prospects of such a compressed electroweak sector at a future high energy Muon Collider operating at 10 TeV. Focusing on vector boson fusion (VBF) production of inert scalar pairs, I will demonstrate how forward muon tagging provides a powerful handle to isolate signal events in scenarios where traditional missing energy based searches fail. After reviewing the relevant dark matter and experimental constraints on the IDM parameter space, I will present a detailed collider analysis using both cut-based methods and multivariate techniques. The impact of detector energy resolution will be discussed, highlighting the importance of precision instrumentation. Our results show that even in highly compressed and experimentally challenging scenarios, the clean environment and forward coverage of the Muon Collider can significantly enhance discovery potential, making it a compelling probe of dark sectors.

Lepton Flavor Universal New Physics in B-Decays?

Date: 2025-07-22
Speaker: Dr. N Rajeev, PRL
Venue: Room no: 469 (Main Campus)

Abstract

"The flavor-changing neutral current (FCNC) semileptonic decays of B mesons offer a powerful avenue to indirectly probe New Physics (NP) beyond the Standard Model (SM). I will review the current status of the so-called B anomalies. While lepton flavor universality (LFU) ratios such as RK and RK∗ are in good agreement with SM predictions, notable deviations persist in individual branching fractions—for instance, B(B+ → K+μ+μ−) and B(B+ →K+e+e−), both of which deviate at the 4 − 5σ level. Additionally, the angular observable P'5 in B → K∗μ+μ− exhibits a 3.3σ deviation, and a 3.6σ discrepancy is reported in B(Bs → φμ+μ−). Although the recent measurement of Rφ is consistent with the SM, the individual branching fractions remain at odds with expectations. These persistent anomalies hint at NP contributions in both muon and electron sectors. Given that experimental bounds on b → see transitions are still relatively loose, NP might also manifest in the first-generation lepton sector. Motivated by these observations, we perform a global analysis of dimension-6 SMEFT operators, considering the possibility of NP contributions not only in b → sμμ transitions but also in b → see transitions."

On the T-linear resistivity of cuprates: theory

Date: 2025-07-14
Speaker: Prof. Navinder Singh, PRL
Venue: Room no: 469 (Main Campus)

Abstract

"By partitioning the electronic system of the optimally doped cuprates in two electronic components: (1) mobile electrons on oxygen sub-lattice; (2) localized spins on copper sub-lattice, and considering the scattering of mobile electrons (on oxygen sub-lattice) via generation of paramagnons in the localized sub-system (copper spins), we ask what should be the electron-paramagnon coupling function Mq so that T-linear resistivity results both in the low temperature limit (kBT << ~ωqcut) and in the opposite high temperature limit (qcut is a characteristic paramagnon cut-off wave vector). This ’reverse engineering approach’ leads to |Mq| scaling inversely with wave vector. We comment how can such exotic coupling emerge in 2D systems where short range magnetic fluctuations resides. In other words, the role of quantum criticality is found to be crucial. And the low temperature T-linear behaviour of resistivity demands that the magnetic correlation length scales as ξ(T) scales as 1/T which seems to be a reasonable assumption in the quantum critical regime of cuprates (that is, near optimal doping where T-linear resistivity is observed). "

"Modeling Superconductivity, Magnetism, and Quantum Phenomena in Complex Materials"

Date: 2025-06-24
Speaker: Dr. Smritijit Sen, University of Florence
Venue: Online--- https://imeet.vconsol.com/join/4438320547?be_auth=MjE2MTAy

Abstract

We present a comprehensive exploration of quantum materials through state-of-the-art theoretical and computational techniques. Focusing on superconductivity, we delve into intra- and interband pairing mechanisms via Eliashberg formalism and model Hamiltonians, examining how pressure and doping drive Lifshitz transitions. The impact of magnetic impurities on superconducting states is analyzed using density functional theory (DFT) and Green’s function methods with potential applications in developing robust qubit platforms for quantum computing. We further investigate electronic structures through band dispersion, Fermi surfaces, and density of states to interpret experimental probes such as ARPES and IETS. We also highlight structure-property correlations under thermal perturbations, advanced crystal structure prediction using evolutionary algorithms like USPEX, and ongoing work on the optical and photocatalytic properties of mixed anionic systems, including thio-apatites with potential for solar-driven hydrogen production.

Probing collective response in the quantum system using Raman scattering

Date: 2025-06-17
Speaker: Dr. Surajit Sarkar, CEA Grenoble, France
Venue: Online---https://imeet.vconsol.com/join/8046909791?be_auth=NDgyMTQy

Abstract

"Raman scattering is an inelastic light scattering process in which energy is transferred from incident light to the system, and the strongest signal often appears in the absorption spectrum from the collective mode present in the quantum system. In the first part of the talk, I will present a novel effect arising from inversion symmetry broken spin-orbit coupling (SOC) on charge collective modes, plasmons, and how this could be studied using electronic Raman scattering. I will discuss that isolated plasmons could be strongly prominent in resonant eRS in the presence of spin momentum locking SOC in BiTeI, which were invisible previously due to standard $q^2$ suppression, where $q$ is the momentum transferred by the light. The last part of the talk is on Raman response in superconductors. Here, I will discuss the electronic Raman response (eRS) of multiband SC in both A1g and B1g channels across the time reversal symmetry broken transition and the potential possibility of Leggett and Bardassis-Schreiffer modes in the observed spectrum, depending on the nature of the ground state. We will also see from our results that eRS could be used as a probe to detect spontaneously broken time reversal symmetry of superconductors such as s+is and s+id states."

Neutrinoless double beta decay in an realistic SU(5) Model

Date: 2025-05-20
Speaker: Debashis Pachhar, PRL
Venue: Room no: 469 (Main Campus)

Abstract

Baryon number (B) and lepton number (L) are accidental global symmetries of the Standard Model (SM). Any observed violation of these quantum numbers would provide unambiguous evidence for physics beyond the SM. Grand Unified Theories (GUTs) offer a well-motivated framework to study such violations. In this seminar, I will discuss the role of heavy scalar fields in mediating lepton number violation via neutrinoless double beta decay (0νββ) within the SU(5) framework. While the minimal SU(5) setup predicts extremely suppressed contributions to 0νββ due to the heavy scalar masses – as a consequence of the proton decay bound, we will show that this limitation can be circumvented by extending the model. Specifically, the introduction of a discrete ℤ3 symmetry and the inclusion of an additional 15-dimensional scalar representation allow for dominant contributions to the decay process. Such an extension not only remains consistent in yielding realistic fermion mass spectra but also leads to experimentally testable predictions in upcoming ton-scale 0νββ searches.

Electron-phonon coupling induced topological phase transitions in an α-T3 quantum spin Hall insulator

Date: 2025-05-13
Speaker: Dr. Kuntal Bhattacharyya, IIT Guwahati
Venue: Room no: 469 (Main Campus)

Abstract

We study the phenomenon of topological phase transitions induced by electron-phonon (e-ph) coupling in an α-T3 quantum spin Hall insulator that presents smooth tunability between graphene (α = 0) and dice (α = 1) lattice. Upon deriving an effective electronic model under suitable transformations, we come across different regimes of α, which host distinct topological transitions solely mediated through e-ph coupling, manifesting robust support from the bulk gap closing and the relative changes in the topological invariant together with the edge state features. The critical e-ph strengths of these transitions strongly depend on α. We also observe the evidence of an emergent second-order topological insulator (SOTI) phase in our system, which is characterized by the existence of corner modes and its topological marker. Interestingly, these corner modes are wiped out beyond a critical e-ph coupling (albeit different for different α), referring to a SOTI-trivial phase transition induced by the e-ph coupling.

Study of Neutrino Oscillation with non unitarity

Date: 2025-05-06
Speaker: Pathan Tamanna, National Institute of Technology Surat
Venue: Room no: 469 (Main Campus)

Abstract

In this talk we will present the neutrino oscillation probabilities in presence of a non unitary mixing matrix . We will show the oscillation probabilities both in vacuum and including matter effects, Using the expressions of probabilities derived, we will show at which energies and baselines the signature of non unitary will be significantly different from standard scenarios.

Neutrinos in Cosmology

Date: 2025-05-01
Speaker: Sanjit Kumar, NIT Jamshedpur
Venue: Room no: 469 (Main Campus)

Abstract

In this talk, we will begin by introducing the basics of neutrinos and their significant role in cosmology. We will discuss the thermodynamics of the early universe and examine the Boltzmann equation and the process of neutrino decoupling. Moving forward, we will explore the nature of dark matter and investigate whether neutrinos could serve as viable dark matter candidates. We will then review cosmological constraints on neutrino masses. Finally, we will discuss the possibility of sterile neutrinos as dark matter. Throughout the talk, we aim to highlight how neutrinos influence key processes in the early universe and their relevance in modern cosmology.

Static structure factor and the dispersion of the Girvin-MacDonald-Platzman density mode for fractional quantum Hall fluids on the Haldane sphere

Date: 2025-04-22
Speaker: P. Rakesh Kumar Dora, The Institute of Mathematical Sciences, Chennai
Venue: Room no: 469 (Main Campus)

Abstract

We study the neutral excitations in the bulk of the fractional quantum Hall (FQH) fluids generated by acting with the Girvin-MacDonald-Platzman (GMP) density operator on the uniform ground state. Creating these density modulations atop the ground state costs energy since any density fluctuation in the FQH system has a gap stemming from underlying interparticle interactions. We calculate the GMP density-mode dispersion for many bosonic and fermionic FQH states on the Haldane sphere using the ground state static structure factor computed on the same geometry. Previously, this computation was carried out on the plane. Analogous to the GMP algebra of the lowest Landau level (LLL) projected density operators in the plane, we derive the algebra for the LLL-projected density operators on the sphere, which facilitates the computation of the density-mode dispersion. Contrary to previous results on the plane, we find that, in the long-wavelength limit, the GMP mode accurately describes the dynamics of the primary Jain states."

Higher-Order QCD Corrections and Threshold Resummation for Processes in the Standard Model and Beyond at Hadron Colliders

Date: 2025-04-11
Speaker: Chinmoy Dey, IIT Guwahati
Venue: Online--- https://imeet.vconsol.com/join/9927407570?be_auth=NjU4MDkx

Abstract

In this talk, we present our study on threshold resummation for various Standard Model processes at the Large Hadron Collider (LHC), including neutral and charged Drell-Yan production, Higgs boson production in association with a massive vector boson, and Higgs production via bottom quark annihilation. We perform resummation up to N³LO+N³LL accuracy in QCD, addressing the large logarithms that arise in the partonic threshold limit. Additionally, we analyzed the gluon fusion channel for ZH production, resumming contributions up to NLO+NLL accuracy in the Born-improved theory and combining them with Drell-Yan-type contributions. For on-shell ZZ pair production, we extend the resummation accuracy to NNLO+NNLL. After performing the threshold resummation, the theoretical uncertainties are reduced compared to fixed-order results. Furthermore, we investigate the two-loop corrections to the decay of a pseudo-scalar Higgs boson (A) into three partons, including higher-order terms in the dimensional regulator. These results are crucial for improving theoretical predictions for pseudo-scalar production with one jet at hadron colliders.

Hidden’ magnetism and a mechanism for it

Date: 2025-03-25
Speaker: Dr. Aabhaas Vineet Malik, Birla Institute of Technology and Science Pilani, KK Birla Goa campus
Venue: Room no: 469 (Main Campus)

Abstract

Recently a mysterious hidden magnetic memory, which manifests itself in the form of “spontaneous” vortices appearing in the superconducting state of 4Hb-TaS2, was reported [Nature, 607,692, 2022]. Motivated by this observation, we present a mechanism which leads to a similar phenomenology. The mechanism relies on spin-charge separation induced by strong electronic correlations in a flat-band tuned away from half filling, which is the expected picture of the T-layers in 4Hb-TaS2. For concreteness, we demonstrate the feasibility of this mechanism within a square lattice t-J model. Our results pave the way towards understanding the observed magnetic memory effect and may apply to a broader class of materials.

Towards Quantum Simulating QCD

Date: 2025-03-25
Speaker: Dr. Indrakshi Raychowdhury, Birla Institute of Technology and Science Pilani, KK Birla Goa campus
Venue: Room no: 469 (Main Campus)

Abstract

Being created from the Big Bang - evolved to families of sub-atomic particles - landing in an astrophysical environment -the dynamic properties of the strong interactions of nature are still unknown. Simulating the dynamics of quantum chromodynamics (QCD) is beyond the scope of even the most powerful supercomputers. Standing at the end of the first quarter of the century, the question is whether a quantum computer can (/will be able to) simulate nature. Okay, yes, it should. The visionary physicist Richard P. Feynman envisioned that "Nature isn't classical, dammit, and if you want to make a simulation of nature, you'd better make it quantum mechanical..." After almost half a century as quantum technology matures it appears to be close to a reality. Yet, as Feynman envisioned, the task remains challenging and requires substantial advancement in `qubitizing/quditizing’ nature - develop novel quantum algorithms and implement them on quantum hardware. In this talk, I'll briefly summarize the journey towards quantum simulating QCD - the challenges, advances and prospects.

From Monopole-Induced Berry Phase to Quadrupolar Berry Phase

Date: 2025-03-21
Speaker: Prof. Sourin Das, Indian Institute of Science Education and Research, Kolkata
Venue: Room no: 469 (Main Campus)

Abstract

We explore the Berry phase associated with purely quadrupolar states (⟨ψ|S|ψ⟩ = 0) in spin-1 systems. By employing the Majorana stellar representation, we demonstrate the topological nature of the quadrupolar Berry phase, revealing that it takes values of either 0 or π, and establish its connection to the exchange of Majorana stars. Additionally, we investigate the dynamics of a state within the quadrupolar subspace under the influence of a static magnetic field. The time evolution governed by this Hamiltonian confines the system to the quadrupolar subspace, generating a geometric phase of the Aharonov-Anandan type, quantized to 0 or π. We also present a natural framework for understanding the topological properties of this subspace in terms of anti-unitary symmetries. Finally we will discuss a possible application of our findings to Holographic quantum codes and robust quantum phase gates.

LCSR application to D+ → π+l+l−

Date: 2025-02-13
Speaker: Dr. Anshika Bansal
Venue: Room no: 469 (Main Campus)

Abstract

Flavour Changing Neutral Currents (FCNCs) in the Standard Model (SM) arise only at loop level, making them important probes for New Physics (NP). However, unlike bottom FCNCs (for example b → s l+l−), the charm FCNCs (for example c → u l+l− ) are dominated by long distance (LD) effects due to strong GIM suppression, posing significant challenges. In this talk we will explore these challenges focusing on decays D+ → π+l+l− which can be realised as the combination of the singly Cabibbo suppressed (SCS) weak transitions with the electromagnetic emission of the lepton pair. We study these LD effects using the framework of Light Cone Sum Rules (LCSR) and make predictions for the differential widths for these decays. Our findings suggest that the weak annihilation contributions are dominant, with negligible loop contributions. Finally, I relate these decays to other Cabibbo favoured and doubly Cabibbo suppressed, D(s)+ → P l+l− (P = π, K... ) decays through flavour symmetries. As a byproduct, I further discuss Ds+ → π+l+l−, which is not an FCNC but shares the topologies with D+ → π+l+l−, and can therefore be useful in better understanding of LD dynamics involved.

Puzzles and predictions of the left right symmetric model

Date: 2025-02-06
Speaker: Dr. Ravi Kuchimanchi
Venue: Room no: 469 (Main Campus)

Abstract

We will show that O(1) leptonic CP violation generates too large a strong CP phase in one loop RGE running, and therefore the Minimal Left Right Symmetric Model (with triplet and bidoublet Higgses) is testable regardless of the scale of parity breaking by the following prediction: The neutrino experiments will not discover leptonic CP violation in the PMNS matrix. Moreover the lepton mass hierarchy can be understood in this model if the electron mass is radiatively generated in 2 loop RGE.

Non-Fermi Liquid Transport in Semimetals and Strongly Correlated Systems

Date: 2025-01-30
Speaker: Dr. Abhishek Samanta, IIT Gandhinagar
Venue: Room no: 469 (Main Campus)

Abstract

The Hall coefficient traditionally measures the density of charge carriers in metals, via Drude’s inverse carrier density relation. However, this relation may break down due to intriguing Fermi surface topology or strong electronic interaction. Using a recently developed thermodynamic formalism, we study deviations of the Hall coefficients from Drude's relation in (1) semimetals (e.g., Weyl, nodal-line) and (2) the Hubbard model. Our calculations explain the "Hall anomaly", characterized by a divergence of the Hall coefficient near half-filling and an abrupt sign change, observed in cuprate experiments. Finally, I will briefly discuss similar anomalies in thermopower, studied via the calculation of the Seebeck coefficient of strongly interacting systems.

In-In EFT, the In-Out way

Date: 2025-01-21
Speaker: Prof. Namit Mahajan
Venue: Room no: 469 (Main Campus)

Abstract

In-In correlators are the natural quantities in time dependent settings like cosmology or in non-equilibrium situations when the interest in not in scattering matrix elemnts but rather expectation values. The talk will describe an attempt to have an effective field theory (EFT) description for In-In correlators in terms of the more familiar In-Out formalism routinely used for S-matrix calculations.

Exploding Stars, Shapeshifting neutrinos, and the Synthesis of Heavy Elements

Date: 2025-01-16
Speaker: Dr. Amol V. Patwardhan, New York Institute of Technology, USA
Venue: Online--- https://imeet.vconsol.com/join/1447710668?be_auth=NTg3MTQz

Abstract

How exactly do stars explode? Where and how are the elements that we observe in the cosmos synthesized? A common theme tying these questions together is the abundant presence of neutrinos – mysterious and elusive elementary particles – in these environments. In this talk, I shall describe how neutrinos can power these magnificent cosmic explosions, i.e., supernovae, and also aid in the synthesis of heavy elements thereafter. Particular attention will be given to a longstanding open question: the origin of proton-rich isotopes in nature. I will present some interesting results from my recent work, demonstrating how a once-popular solution to this conundrum still endures, despite a decade's worth of claims to the contrary. Finally, I shall briefly discuss some peculiar behaviors of neutrinos, such as their penchant for shapeshifting (flavor oscillations), or their potential to quantum-entangle as they interact with each other in these environments.

Anderson localization in QFT and hierarchies from nonlocality

Date: 2025-01-07
Speaker: Dr. Ketan Patel, THEPH
Venue: Room no: 469 (Main Campus)

Abstract

It was shown in [1710.01354] that disordered local interactions in theory space can localize mass eigenstates (analogous to Anderson localization in disordered lattice) enabling exponentially hierarchical couplings in QFT. In this talk, I shall show that such theories can also produce multiple massless modes. Subsequently, deterministic nonlocality can give rise to hierarchies that are qualitatively distinct from the original proposal.

Complete escape from localization on a hierarchical lattice: A Koch fractal with all states extended

Date: 2025-01-02
Speaker: Sougata Biswas, Presidency University
Venue: Online--- https://imeet.vconsol.com/viewer/1718585506?be_auth=NTIwNzYy

Abstract

"An infinitely large Koch fractal is shown to be capable of sustaining only extended, Bloch-like eigenstates if certain parameters of the Hamiltonian describing the lattice are numerically correlated in a special way, and a magnetic flux of a special strength is trapped in every loop of the geometry. We describe the system within a tight-binding formalism and prescribe the desired correlation between the numerical values of the nearest-neighbor overlap integrals, along with a special value of the magnetic flux trapped in the triangular loops decorating the fractal. With such conditions, the lattice, despite the absence of translational order of any kind whatsoever, yields an absolutely continuous eigenvalue spectrum and becomes completely transparent to an incoming electron with any energy within the allowed band. The results are analytically exact. An in-depth numerical study of the inverse participation ratio and the two-terminal transmission coefficient corroborates our findings. Our conclusions remain valid for a large set of lattice models, built with the same structural units, but beyond the specific geometry of a Koch fractal, unraveling a subtle universality in a variety of such low-dimensional systems. Reference: S. Biswas and A. Chakrabarti, Physical Review B 108, 125430 (2023)."

2024

Effective theories at finite temperature

Date: 2024-12-19
Speaker: Prof. Subhendra Mohanty, IIT Kanpur
Venue: Room no: 469 (Main Campus)

Abstract

Effective theories offer an economical way to test the predictions of diverse UV complete theories in low energy experiments. The finite temperature formulation of effective theories is needed for applications in cosmology and collider experiments in phase transitions, quark gluon plasma, Casimir effect etc. I will discuss a way to formulate effective theories at finite temperature using the Heat Kernel Method which involves the calculation of finite temperature corrections to the Wilson coefficients. I will illustrate the results with a calculation of Coleman-Weinberg potential for the Higgs-Effective field theory and apply it in testing the nature of phase transition from different extensions of the standard model. Of particular interest is the emergence of Polyakov loops as a parameter which has applications in phase transitions and spin-systems in condensed matter.

Solving the strong CP puzzle through Radiative mass mechanism

Date: 2024-12-16
Speaker: Gurucharan Mohanta, SRF
Venue: Room no: 469 (Main Campus)

Abstract

I will briefly outline the radiative mechanism for fermion mass generation and focus on how it can address the strong CP problem. To do this, the mechanism is implemented within a parity-invariant Left-Right symmetric framework. In this setup, loop-induced fermion masses arise from corrections involving a new flavor-non-universal gauge boson and heavy fermions. The required non-universal U(1) symmetry for the mechanism is an all-fermion version of the $L_\mu - L_\tau $ symmetry. The minimal model predicts that the mass of the U(1) gauge boson and the scale of right-handed sector breaking are of the same order. This leads to a strong CP phase of the order of $10^{-14} $.

A leisurely walk through few exotic manifestation of interacting spin systems

Date: 2024-12-11
Speaker: Dr. Saptarshi Mandal
Venue: Room no: 469 (Main Campus)

Abstract

In the talk we discuss some of the fascinating aspects of frustrated magnetism in a few systems of our interest. We begin with a discussion of the origin of frustration in model systems through examples of geometric and exchange effects. The manifestation of frustration giving degenerate ground states, order-disorder phenomena through quantum fluctuations are explained in the Hollandite lattice system. Next the ground state of varieties of systems following ice rules are explained and how emergent electrodynamics is obtained are outlined. Finally we introduce Kitaev model and explain the effect of frustration and give a pedagogical exposition to abelian and non-abelian anyons or Majorana fermions obtained in this system.

Surface Tension of a Topological Phase

Date: 2024-12-06
Speaker: Dr. Adhip Agarwala
Venue: Room no: 469 (Main Campus)

Abstract

Metastable phases, in general, are unstable to nucleating droplets of the order defining the global free energy minima. However, whether such a droplet grows or shrinks relies on a competition between the surface tension and bulk energy density. We study the role of coupling a topological fermionic field to a scalar field undergoing such nucleation processes. We find that existence of nontrivial fermionic boundary modes on the nucleating droplets leads to substantial quantum corrections to the surface tension thereby modifying the size of the critical nucleus beyond which unrestricted droplet growth happens. To illustrate the phenomena we devise a minimal model of fermions in a Chern insulating system coupled to a classical Ising field in two spatial dimensions. Using a combination of analytic and numerical methods we conclusively show that topological phases can lead to characteristic quantum surface tension. In this talk I will try to motivate some of these questions, and provide a general overview of quantum condensed matter landscape.

Unveiling the mechanism behind sign changes in the thermopower and Hall coefficient of strained Sr2RuO4

Date: 2024-12-04
Speaker: Dr. Sudeep K. Ghosh, IIT Kanpur
Venue: Room no: 469 (Main Campus)

Abstract

Sr2RuO4 is a fascinating material in condensed matter physics, celebrated for its unconventional superconductivity and intricate electronic structure. A particularly intriguing aspect is its strain-induced Lifshitz transition, which profoundly influences transport properties. Notable among these effects are the sign changes observed in the thermopower and Hall coefficient under strain, a phenomenon that remains not fully understood. In this talk, I will explore these transport properties using the semiclassical Boltzmann transport formalism, examining both unstrained and strained (uniaxial and c-axis) systems. I will demonstrate that the sign changes are driven by the Van Hove singularity, which emerges as a direct consequence of the Lifshitz transition, offering deeper insights into the electronic structure and transport behavior of Sr2RuO4.

Introduction to High-Energy Neutrino Astrophysics

Date: 2024-12-02
Speaker: Dr. Bhupal Dev, Washington University, USA
Venue: Room no: 469 (Main Campus)

Abstract

We will provide a pedagogical introduction to High-Energy Neutrino Astrophysics and the emerging field of Multimessenger Neutrino Astronomy. We will discuss how the high-energy neutrinos are produced, propagate and are detected and what they can tell us about the origins of cosmic rays, dark matter, and other fundamental puzzles of the Universe.

Collider fingerprints of freeze-in dark matter

Date: 2024-11-29
Speaker: Dr. Anupam Ghosh, PDF, PRL
Venue: Room no: 469 (Main Campus)

Abstract

We examine a simple dark sector extension where the observed dark matter (DM) abundance arises from a freeze-in process through the decay of heavy vector-like quarks into a scalar dark matter candidate. The detection prospects of such DM are challenging due to the feeble nature of the interactions, but these vector-like quarks can be produced copiously at the LHC, where they decay to Standard Model quarks along with DM. Depending on the decay rate, this scenario is typically probed through long-lived particle or displaced vertex signatures, assuming a radiation-dominated background. An alternative hypothesis suggests that the Universe may have experienced a rapid expansion phase instead of the standard radiation-dominated one during freeze-in. This would significantly alter the dark matter phenomenology, requiring a substantial increase in the interaction rate to match the observed relic density, resulting in the rapid decay of the parent particle. As a result, much of the parameter space for this scenario is beyond the reach of traditional long-lived particle and displaced vertex searches. Due to this non-standard cosmic evolution, existing constraints do not cover the expanded dark matter parameter space. We propose a complementary search strategy to explore this scenario, offering additional limits alongside searches for long-lived particles and displaced vertices. In our search, we investigate the FIMP dark matter model at the LHC using boosted fatjets and significant missing transverse momentum. To improve precision, we include one-loop QCD corrections for LHC production processes and employ a boosted decision tree multivariate analysis, leveraging jet substructure variables to explore a vast parameter space for this minimally extended FIMP dark matter model at the 14 TeV LHC.

Neutrinos: Dirac or Majorana

Date: 2024-11-26
Speaker: Dr. Bhupal Dev, Washington University, USA
Venue: Room no: 469 (Main Campus)

Abstract

Whether neutrinos are Dirac or Majorana particles is an open question in fundamental physics. Theoretically, it is also possible that neutrinos are pseudo-Dirac, which are fundamentally Majorana fermions, but essentially act like Dirac fermions in most experimental settings, due to extremely small active-sterile mass splitting. Such small values of mass splitting can be accessed via active-sterile oscillations over an astrophysical baseline. We use the recent multi-messenger observations of high-energy neutrino sources to probe hitherto unexplored values of active-sterile mass splitting, which improve the reach of terrestrial experiments by more than a billion.

Implications of Residual modular symmetries on neutrino masses and mixing

Date: 2024-11-11
Speaker: Dr. Monal Kashav, PDF, THEPH
Venue: Room no: 469 (Main Campus)

Abstract

"This talk explores the implications of modular invariance for neutrino mass matrices at the self-dual point τ=i. Assuming both exact self-duality and modular form for the neutrino Yukawa couplings provides some new insights into neutrino mass and mixing patterns. "

Large Blue Spectral Index from a Conformal Limit of a Rotating Complex Scalar

Date: 2024-10-22
Speaker: Dr. Sai Chaitanya Tadepalli, Indiana University, USA
Venue: Room no: 469 (Main Campus)

Abstract

CDM isocurvature power with large blue spectral index can explain the 2-sigma hint in Planck data and recent JWST observation of high redshift galaxies. A well-known method for generating a large blue spectral index for axionic isocurvature perturbations involves a flat direction without a quartic potential term for the axion field's radial partner. In this talk, we discuss how a large blue spectral index can be achieved even with a quartic potential term linked to the Peccei-Quinn symmetry breaking radial partner. We utilize the fact that a large radial direction with a quartic term can naturally induce a “conformal limit”, producing an isocurvature spectral index of 3. Alternatively, this limit can be seen as the angular momentum of the initial conditions slowing the radial field or as a superfluid limit. The large angular momentum necessitates a careful quantization process to establish the vacuum state. We outline the parametric region that aligns with axion dark matter and isocurvature cosmology, and discuss prospects for future detection.

Quantum aspects of the conformal sector of gravity and torsion in 4D

Date: 2024-10-07
Speaker: Mr. Abbas Tinwala
Venue: Online---https://imeet.vconsol.com/viewer/5845393127?be_auth=NTIzNzU2

Abstract

"Classical conformal invariance is expected to hold quite well at energies MSM ≪ E≪ MP. so that the Standard Model (SM) particle masses, MSM, may be neglected while at the same time, quantum gravity can be assumed to contain only massless spin-2 particles. Coincidentally, consistent theory of propagating torsion coupled to SM particles is possible only for massless fermions which can be realized if E Mfer ≫ for the mass Mfer of heaviest fermions. In addition to fermions if torsion is coupled to scalar fields then the theory of propagating torsion is not possible due to unitarity violations found at the two-loop order. In this regard, recently proposed theories of composite Higgs particles which indicate that the Higgs field manifests as fermionic condensate could be a sign of relief for the torsion theory since at energies higher than the electroweak scale one ends up only with fermions (and bosons with non-zero spin). Even in this scenario, there may still be an obstacle to realizing the theory of propagating torsion since we must deal with the conformal sector of gravity. In this talk, I will show that the anomaly-induced effective action including torsion [3], consists of a scalar field representing the conformal sector of gravity coupled to torsion potentially causing similar unitary violations. A calculation of one loop and/or two loop divergences in the theory of conformal factor and torsion and a subsequent analysis of the beta functions become necessary to clarify the status of torsion as a propagating field."

Josephson diode effect in a quantum dot junction

Date: 2024-09-24
Speaker: Dr. Debika Debnath
Venue: Room no: 469 (Main Campus)

Abstract

I will discuss the Josephson diode effect (JDE) in a quantum dot (QD)-based Josephson junction (JJ) in the presence of an external magnetic field and Rashba spin-orbit interaction (RSOI). To achieve the diode effect in the JJ, we break the time-reversal symmetry through the Zeeman field, and the inversion symmetry is broken by RSOI. We calculate the Josephson current using the Keldysh nonequilibrium Green’s function technique. Our QD with RSOI induces JDE in the heterojunction with a large rectification coefficient (RC) that can be tuned to be as high as 70% by an external gate potential, indicating a giant JDE in our QD junction. Interestingly, we find that the sign and magnitude of the RC are highly controllable by the magnetic field and RSOI. We also investigate the role of electron-electron correlation to the Josephson diode by incorporating an interacting QD as the intermediate tunnelling medium. Our proposed QD–based Josephson diode (JD) has the potential to be an efficient superconducting device component.

Quasiperiodic potential induced corner states in a quadrupolar insulator: A paradigm for higher-order topology

Date: 2024-09-18
Speaker: Prof. Saurabh Basu
Venue: Room no: 469 (Main Campus)

Abstract

The topological and localization properties of a quadrupolar insulator represented by the celebrated Benalcazar-Bernevig-Hughes model is studied in presence of a quasiperiodic disorder. While disorder is expected to disturb the existence of topological order in a system, we observe that a disorder driven topological phase emerges where the original (clean) system demonstrates trivial behavior. This phenomena is confirmed by the re-emergence of the zero energy states together with the non-trivial values of the quadrupole moment. Moreover, the distribution of the excess electronic charge shows a pattern that clearly corresponds to the bulk quadrupole topology. To elaborate upon the localization properties of the mid-band states, we compute the inverse participation and normalized participation ratios. It is observed that the in-gap states become critical (multifractal) at the point that discerns a transition from a topological localized to a trivial localized phase. Finally, we carry out a similar investigation to ascertain the effect of the quasiperiodic disorder on the quadrupolar insulator when the model exhibits topological properties in the absence of disorder. Again, we note a multifractal behavior of the eigenstates in the vicinity of the transition.

Pseudogap in

Date: 2024-09-05
Speaker: Dr. Jalaja Pandya
Venue: Room no: 469 (Main Campus)

Abstract

Gor'kov and Teitel'baum formulated a phenomenological model for the number of charge carriers, derived from the Hall effect data of La2-xSrxCuO4. The activation energy obtained from this model agreed well with the pseudogap signatures observed in the angle resolved photoemission spectroscopy. Recently, Hall eﬀect measurements are done on Lanthanum doped Strontium Iridate

Efficient Quantum Field Theories for Quantum Computers

Date: 2024-09-03
Speaker: Dr. Debashis Banerjee
Venue: Room no: 469 (Main Campus)

Abstract

"Computing methods on classical computers have dominated the discovery frontline from fundamental physics for several decades now. It is however becoming clear that at least in physics, there are several computational avenues (such as finite density and real-time dynamics) where development can be accelerated via quantum computers. At the same time, improving classical computing techniques using clever analytical insights is essential to provide further inputs to the quantum computing frontier. In this talk, we will discuss the broad ideas behind the novel constructions and selected applications illustrating results for realistic systems in condensed matter and particle physics. Such scenarios are expected to be realized in quantum hardware in the recent future."

"Non-equilibrium (hot) electron relaxation: Review of the ultrafast phenomena in metals and superconductors. "

Date: 2024-08-22
Speaker: Prof. Navinder Singh
Venue: Room no: 469 (Main Campus)

Abstract

"This field effectively originated when Kaganov, Lifshitz and Tantarov in 1957 put forward their famous Two-Temperature Model (TTM) of non-equilibrium electron relaxation in metals. During the ensuing decades much advance happened due to the advent of femtosecond lasers. In this talk, a chronological review of the field will be presented in which relaxation of hot (non-equilibrium) electrons in semiconductors and superconductors will be discussed. Some works done in PRL in this field will be reviewed. Recent advancement of photo-induced superconductivity will also be discussed."

NLP corrections for H+ jet production

Date: 2024-08-21
Speaker: Dr. Sourav Pal, PDF
Venue: Room no: 469 (Main Campus)

Abstract

Precise experimental data from the Large Hadron Collider and the lack of any persuasive new physics signature demand improvement in the understanding of the Standard Model.The scattering cross-sections are plagued with Leading power (LP) and next-to-leading power (NLP) logarithms. Resummation of LP logarithms has a long history of almost three decades and their resummation methods are well known in the present literature. However, precise prediction also requires the resummation of NLP logarithms, as they have a sizeable numerical impact in the cross-section calculation. These NLP logarithms for colour singlet processes are well known in the literature, however, there is a scarcity of results when final state colour particles are involved in the scattering process. In the talk, I will discuss a new method of calculating the NLP logarithms where final state colour particles are involved and will show its application for Higgs+ jet production.

Implications of decaying neutrino state in the Bi-magic baseline

Date: 2024-08-16
Speaker: Dr. Supriya Pan, PDF
Venue: Room no: 469 (Main Campus)

Abstract

"The neutrino oscillations have established that there are massive neutrino mass states. The well-understood framework of standard three-flavor neutrino oscillation gives us the scope to look for signatures of new physics beyond the Standard Model. One such scenario is when heavier neutrino states decay into lighter ones, first proposed to describe the zenith-angle dependence in atmospheric-neutrino data at Super-Kamiokande. The baseline of 2540 km has a special feature where the sensitivity to mass hierarchy is very high at probability maxima. In our work, we study how the presence of decay of the heaviest neutrino state will impact the sensitivity to mass-hierarchy and the octant of angle theta23 using the proposed setup of Portvino to ORCA (P2O) experiment at a baseline of 2588 km."

Beyond standard hydrodynamics: “maximum-entropy” theory and the dynamics of critical fluctuations

Date: 2024-08-01
Speaker: Dr. Chandrodoy Chattopadhyay
Venue: Room no: 469 (Main Campus)

Abstract

I will present formulation of ‘maximum-entropy hydrodynamics’, a far-off-equilibrium macroscopic theory that effectively describes both free-streaming and near-equilibrium regimes of the quark-gluon plasma formed in heavy-ion collisions. Unlike standard hydrodynamic theories this formulation incorporates contributions to all orders in shear and bulk inverse Reynolds numbers, allowing it to handle large dissipative fluxes. By considering flow profiles relevant for nuclear collisions at high energies, I will demonstrate that ‘maximum-entropy hydrodynamics’ provides excellent agreement with underlying kinetic theory throughout the fluid’s evolution, especially in out-of-equilibrium regimes where traditional hydrodynamics becomes inapplicable. I will then present formulation of stochastic fluid dynamics to model the evolution of critical fluctuations in a system that is close to a critical point. I will demonstrate that correlation functions of the order parameter exhibit dynamical scaling behavior which is sensitive to the correlation length and shear viscosity of the fluid. I will also show that non-linear interactions between shear modes constrain the minimum value of a fluid’s shear viscosity.

Heavy-ion collisions and hydrodynamics

Date: 2024-07-31
Speaker: Dr. Chandrodoy Chattopadhyay
Venue: Room no: 469 (Main Campus)

Abstract

Relativistic heavy-ion collisions at LHC, CERN and RHIC, BNL produce a novel state of matter, the quark-gluon plasma (QGP), where the fundamental constituents of nucleons, i.e., quarks and gluons, become deconfined over nuclear volumes. Understanding the thermodynamic and transport properties of QGP constitute one of the major goals of high energy nuclear physics. In this talk, I shall give an overview of heavy-ion collisions and describe how hydrodynamics plays a fundamental role in the modeling of such collisions. I will present how relativistic dissipative hydrodynamics can be systematically formulated using kinetic theory and outline the development of a macroscopic theory that is applicable even in far-off-equilibrium regimes where traditional hydrodynamics breaks down. I will also discuss the incorporation of thermal fluctuations in hydrodynamics and their role in extracting the transport properties of QGP using final state observables of heavy-ion collisions.

Effects of disorder on flat bands of some tight binding models.

Date: 2024-07-12
Speaker: Bharathiganesh D.
Venue: Room no: 469 (Main Campus)

Abstract

The effects of disorder on condensed matter systems where electrons move from one site to another by means of quantum mechanical diffusion described by tight binding models has garnered a lot of interest recently. In one dimension disorders almost always leads to localisation of electrons for lattices of reasonably big size. On the other hand, geometry of the lattice may lead to localisation of electrons at particular sites due to the onset of flat bands. In this talk we will discuss a system where both these localisation effects are present i.e. effects of different disorders on a system with flat bands and the net result of these effects.

Minimal Z' for Radiative mechanism

Date: 2024-07-09
Speaker: Gurucharan Mohanta, SRF
Venue: Room no: 469 (Main Campus)

Abstract

We discuss a mechanism in which the masses of the third, second, and first generation charged fermions are generated at tree level, 1-loop, and 2-loop levels, respectively. In this mechanism, loop-induced masses are obtained through fermionic self-energy corrections induced by heavy gauge bosons of a new single flavorful $U(1)_F$ symmetry, which have flavor-violating interactions with Standard Model fermions. Phenomenologically, the flavor-violating couplings $Q_{ij}$ are desired to have $|Q_{12}|<|Q_{23}|,|Q_{13}|$ because constraints from $K^0$-$\overline{K}^0$ mixing and $\mu$-$e$ conversion in nuclei, involving first and second family fermions, are more stringent than others. We establish a framework to achieve this condition and quantify the optimal flavor violations required to implement the radiative mass generation mechanism.

Exploring scalar dark sector with Peceei-Quinn symmetry at the LHC.

Date: 2024-07-05
Speaker: Dr. Anupam Ghosh
Venue: Room no: 469 (Main Campus)

Abstract

The Inert Higgs Doublet model (IDM), assisted by Peccei-Quinn (PQ) symmetry, offers a simple but natural framework of a dark sector that accommodates Weakly Interacting Massive Particle (WIMP) and axion as dark matter components. Spontaneous breaking of $U(1)_{PQ}$ symmetry, which was originally proposed as an elegant solution to the strong charge-parity (CP) problem, also ensures the stability of WIMP through a residual $\mathbb{Z}_2$ symmetry. Interestingly, additional fields necessitated by PQ symmetry further enrich the dark sector. These include a scalar field proprietor for axion DM and a vector-like quark (VLQ) that acts as a portal for the dark sector through Yukawa interactions. Moreover, this combination of the axion and WIMP components satisfies the observed DM relic density and reopens the phenomenologically exciting region of the IDM parameter space where the WIMP mass falls between 100 - 550 GeV. We investigate the model-independent pair production of VLQs exploring this region at the Large Hadron Collider (LHC), incorporating the effects of next-to-leading order (NLO) QCD corrections. After production, each VLQ decays into a top or bottom quark accompanied by an inert scalar, a consequence of the residual $\mathbb{Z}_2$ symmetry. Utilising relevant observables with a leptonic search channel and employing multivariate analysis, we demonstrate the ability of this analysis to exclude a significant portion of the parameter space with an integrated luminosity of 300 $\text{fb}^{-1}$.

Physics Informed Neural Networks

Date: 2024-06-27
Speaker: Deepanshu Srivastava, SRF
Venue: Room no: 469 (Main Campus)

Abstract

Principles like symmetry and invariance are ubiquitous in physics and have significantly influenced machine learning. This seminar explores the integration of physics principles into neural networks for solving complex problems. The development of physics-informed neural networks is examined, focusing on algorithms enforced by physics knowledge to facilitate the discovery of new physics. Specifically, the role of equivariance is discussed, highlighting its contribution to model efficiency and interpretability. The seminar concludes with a discussion on leveraging these techniques in high energy physics and potential future advancements. This approach holds promise for significant improvements in both theoretical insights and practical applications within particle physics.

Relativistic hydrodynamics and its applications in heavy-ion collisions

Date: 2024-06-20
Speaker: Dr. Chandrodoy Chattopadhyay,
Venue: Online---https://imeet.vconsol.com/join/3016457289?be_auth=MzgwMTgw

Abstract

Relativistic heavy-ion collisions at LHC, CERN and RHIC, BNL produce a novel state of matter, the quark-gluon plasma (QGP), where the fundamental constituents of nucleons, i.e., quarks and gluons, become deconfined over nuclear volumes. Understanding the thermodynamic and transport properties of QGP constitute one of the major goals of high energy nuclear physics. Research over the last two decades has established that the bulk evolution of QGP can be remarkably well-described by relativistic hydrodynamics. Although it is traditionally believed that hydrodynamics is applicable only for nearly-equilibrated systems, recent discoveries reveal that it may be successful even for far-off-equilibrium stages of heavy-ion collisions. This leads to a fundamental question pertaining to many-body dynamics: when does a macroscopic system depict hydrodynamic behavior? In this talk I shall present modern formulations of hydrodynamics and use the concept of `non-equilibrium attractors’ to discuss why such formulations are unreasonably effective beyond their expected domain of applicability. I will then present `maximum-entropy hydrodynamics’, a macroscopic theory which can describe both near and far-off-equilibrium regimes of heavy-ion collisions in a single framework. Finally, I will discuss formulations of stochastic hydrodynamics and its extensions to model the evolution of critical fluctuations in a system that is close to a critical point.

SMEFT analysis of charged lepton flavor violating B-meson decays

Date: 2024-06-10
Speaker: Dr. N Rajeev
Venue: Online---https://imeet.vconsol.com/join/6642133707?be_auth=Mjc4NjM0

Abstract

Charged lepton flavor violation (cLFV) processes, potentially important for various Beyond the Standard Model Physics scenarios are analyzed in the Standard Model Effective Field Theory (SMEFT) framework. We consider the most relevant 2 quark-2 lepton (2q2ℓ) operators for the leptonic and semi-leptonic LFV B-decay (LFVBD) processes Bs → µ +e −, B+ → K+µ +e −, B0 → K∗0µ +e −, and Bs → ϕµ−e +. We analyse the interplay among the Wilson coefficients responsible for these LFVBDs and other cLFV processes like CR(µ → e), ℓi → ℓjγ, ℓi → ℓj ℓkℓm and Z → ℓiℓj, to find the maximal possible LFV effects in B-meson decays. We probe the scale of new physics in relation to the constraints imposed by both classes of the LFV decays while considering both the present bounds and future expectations. In view of the proposed experiments at LHCb-II and Belle II to study charged LFV processes, we have also provided the upper limits on the indirect constraints on such LFVBDs. For the processes where B meson is decaying to µ ± and e ∓, we show that new physics can be constrained by an enhancement of 2-4 orders of magnitude on the current sensitivities of the BRs of B+ → K+µ +e −, B0 → K∗0µ +e −and Bs → ϕµ±e ∓.

Mathematical tales of blackhole, gravity and machine learning

Date: 2024-06-06
Speaker: Dr. Arghya Chattopadhyay
Venue: Online---https://imeet.vconsol.com/join/9420300322?be_auth=MTQzNjAy

Abstract

The aim of this talk is to elaborate on the key concepts of my current research and to outline my future research plans during and beyond the Ramanujan fellowship. I will begin by explaining the basics of quantum complexity with simple examples, followed by an intriguing relationship between the algebra of triple systems and the entropy of black holes in 5 and 4 dimensions. Following this, I will discuss our recent observations in these fields, highlighting notable findings and their implications. Next, I will delve into the bare essentials of machine learning (ML), motivating how principles from physics can enhance ML algorithms. This will be followed by an overview of the two avenues of my research plan: theoretical development and machine learning. I will conclude with a brief discussion on the potential impact and future scope of the proposed research plan for Ramanujan Fellowship.

Deciphering the Mysteries of the Long-Lived Particles at the colliders

Date: 2024-06-03
Speaker: Ms. Chandrima Sen
Venue: Online--- https://imeet.vconsol.com/join/4524798341?be_auth=OTExNTQ0

Abstract

Conventional searches at the LHC operate under the assumption that Beyond the Standard Model particles undergo immediate decay upon production. However, this assumption lacks inherent a priori justification. This talk delves into the exploration of displaced decay signatures across various collider experiments. Combining insights from several studies, we show how small Yukawa couplings, compressed mass spectra, and collider boosts lead to distinctive displaced decays, observable at the CMS, ATLAS and proposed future detectors. These phenomena, manifesting within both Type-I and Type-III seesaw mechanisms, and the Vector-like lepton model with non-zero hypercharge, provide a unique insight into the behaviors of neutrinos and dark matter. The seminar highlights the technical challenges and breakthroughs in detecting and interpreting these signatures, emphasizing their significance in probing the depths of the extensions of the Standard Model.

New Ways to Detect Light Dark Matter

Date: 2024-04-19
Speaker: Dr. Anirban Das
Venue: Room no: 469 (Main Campus)

Abstract

In the last few years, direct detection of light sub-GeV dark matter has emerged as a frontier research area. Because of its low energy scales, many condensed matter systems have been proposed as possible target materials. In this talk, I'll briefly review the mechanisms behind a few of them, and introduce two novel ideas. First, to use superconducting quantum devices to measure the power deposition from dark matter scattering. I'll show that the existing data already put competitive limits on the dark matter-nucleon interaction. I'll also describe how bilayer graphene with voltage-tunable band gap can be used to probe sub-MeV dark matter-electron scattering with promising future prospects.

Dark Matter: the Enigma of our Cosmos

Date: 2024-04-18
Speaker: Dr. Anirban Das
Venue: Room no: 469 (Main Campus)

Abstract

We have known about the existence of a dark sector in our Universe for almost 100 years that comprises about 85% of all matter. However, we are still in the dark about its fundamental nature. In this talk, I will describe various evidences of dark matter that we have, and outline a few theoretical ideas to explain its cosmic abundance. Finally, I will give an overview of various experimental endeavors to identify it, such as direct, indirect detection experiments etc.

Let’s slip into inspiral

Date: 2024-04-05
Speaker: Dr. Shilpa Kastha
Venue: Online ---> https://imeet.vconsol.com/join/1736146599?be_auth=NzM2NDU3

Abstract

I will start with a brief introduction to gravitational waves and update about the current detections and my involvement in those. My main focus will be a state-of-the-art discussion on contemporary tests of general relativity with gravitational wave observations and my contributions to developing a few of those.

Radiative Fermion Masses and Strong CP

Date: 2024-03-22
Speaker: Mr. Gurucharan Mohanta
Venue: Room.No:469 (Main Campus)

Abstract

The hierarchical structure of the Standard Model (SM) charged fermions can be explained by the mechanism of radiative generation of fermion masses. In this mechanism, third-generation fermions are allowed tree-level masses, and lighter fermion masses are induced through loops. Implementation of such mechanisms requires extensions of SM. We will discuss a scenario that can possibly generate fermion masses radiatively and possesses a solution to Strong CP.

Implications of very light sterile neutrinos for absolute mass variables

Date: 2024-03-21
Speaker: Mr. Debashis Pachhar
Venue: Room.no: 469 (Main Campus)

Abstract

The framework of three-flavor neutrino oscillation is a well-established phenomenon, but results from the short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and MiniBooster Neutrino Experiment (MiniBooNE), hint at the potential existence of an additional neutrino state characterized by a mass-squared difference of approximately 1 eV². The new neutrino state is devoid of Standard Model (SM) interactions, commonly referred to as the “sterile neutrino” state. In addition, a sterile neutrino with a mass-squared difference of 10^{-2} eV² has been proposed to improve the tension between the results obtained from the Tokai to Kamioka (T2K) and the NuMI Off-axis ν_e Appearance (NOνA) experiments. The hypothesis of an additional light sterile neutrino state introduces four distinct mass spectra. In this talk, we discuss the implications of the above scenarios for the observables that depend on absolute mass of the neutrinos, namely - the sum of neutrino masses (∑) from cosmology, the effective mass of the electron neutrino from beta decay (mβ), and the effective Majorana mass ( mββ) from neutrinoless double beta decay. We show that, some scenarios can be disfavored by the current constraints of the above variables.

Probing the Hidden Universe: Direct and Indirect Searches of Dark Matter

Date: 2024-03-19
Speaker: Dr. Divya Sachdeva
Venue: Online ---> https://imeet.vconsol.com/join/9022656493?be_auth=NTAzNzE4

Abstract

Recent years have seen strong support for dark matter (DM) from observations on a multitude of scales, with a range of experiments operational, approved, or proposed to explore DM theories across various masses. The vastness of the parameter space of DM necessitates exploring model-dependent and model-independent approaches while investigating the symbiosis between astrophysical observations and particle physics experiments. In this talk, I will highlight my past and present research projects where we obtained limits on parameter space of various DM candidates and outline future research plans. I will conclude with a discussion on two key areas of my research plan: a) the impact of potential interaction of DM with Standard Model (SM) in altering its velocity distribution and expanding the detectable parameter space for direct detection experiments; and b) the presence of non-relativistic DM near supermassive black holes, which can lead to high-density DM regions that produce robust annihilation signals, thereby enhancing our indirect search capabilities.

Hearing the Universe Hum with Gravitational Waves and Primordial Black Holes at Pulsar Timing Array: astrophysical, cosmological and particle physics interpretations

Date: 2024-03-18
Speaker: Dr. Anish Ghoshal
Venue: Room no: 469 (Main Campus)

Abstract

We will discuss interpretation of the nHz stochastic gravitational wave background (SGWB) seen by NANOGrav and other Pulsar Timing Array (PTA) Collaborations in the context of supermassive black hole (SMBH) binaries. The frequency spectrum of this stochastic background is predicted more precisely than its amplitude. We will discuss how Dark Matter friction can suppress the spectrum around nHz frequencies, where it is measured, allowing robust and significant bounds on the Dark Matter density, which, in turn, controls indirect detection signals from galactic centers. Next we will discuss alternative cosmological interpretations including cosmic strings, phase transitions, domain walls, primordial fluctuations and axion-like physics each of which may lead to Primordial Black Hole formation. Focussing on primordial black holes (PBHs) production in various cosmological scenarios involving single-field inflation, multiple fields, particularly the Curvaton model, as well as those based on the presence of remnants dominated by the false vacuum and show the PBH formation from these remnants including the contribution from the false vacuum and the bubble walls, during strong first-order phase transition by estimating the collapse using the hoop conjecture. Such PBH formations have associated Gravitational Waves from bubble collisions, the spectral shape of which is distinct from that of scalar-induced GW. Finally we will end by putting these comparative studies to test via We will discuss how well these different hypotheses fit the NANOGrav data, both in isolation and in combination with SMBH binaries, and address the questions: which interpretations fit the data best, and which are disfavoured. Finally we also discuss experimental signatures that can help discriminate between different sources of the PTA GW signals with complementary probes using CMB experiments and searches for light particles in DUNE, IceCUBE-Gen2, neutrinoless double beta decay, and forward physics facilities at the LHC like FASER nu, etc. along with Primordial Black Hole formation and its constraints.

The Gorkov-Teitelbaum thermal activation model for the cuprates

Date: 2024-02-27
Speaker: Prof. Navinder Singh
Venue: Room no: 469 (Main Campus)

Abstract

A brief overview of this very successful phenomenological model for the pseudogapped state of cuprates will be presented. A recent work on the pseudogapped state on a related system (Strontium Iridate) using this model will be discussed.

Soft gluon non-factorizable charm loops in B to K(*) l+l- and implications for new physics

Date: 2024-02-13
Speaker: Prof. Namit Mahajan
Venue: Room no: 469 (Main Campus)

Abstract

I'll discuss some recent progress on computing the non-factorizable soft gluon contribution to B to K(*) l+l- decays arising from charm loops. These constitute a considerable hadronic uncertainty when comparing with the experimental data. Some implications for new physics in these modes will be discussed.

Linking lepton number violation with supersymmetry breaking

Date: 2024-02-07
Speaker: Dr. Ketan M. Patel
Venue: Room no: 469 (Main campus)

Abstract

Supersymmetry and lepton number violation are apparently distinct hypothetical phenomena introduced to address two very fundamental issues of the Standard Model of particle physics: the gauge hierarchy problem and neutrino masses, respectively. In this talk, I will highlight how these phenomena can be linked. Consequences for direct searches, in terms of displaced vertex signatures, shall also be outlined.

Exploring the Dark Sector: New Regimes, New Ideas

Date: 2024-01-15
Speaker: Dr. Anirban Das
Venue: Online---> https://bluejeans.com/613207389/4345

Abstract

The overwhelming evidence from astrophysical and cosmological observations have established the existence of dark matter in our Universe. Even though we know that it forms most of the matter, we do not know anything about its nature. Decades of experiments have not yielded any conclusive detection yet. So it is high time to look beyond the simplest models, and broaden the search for nonstandard theories of particle dark matter and cosmology. In the first part of my talk, I will describe a couple of new proposals to use novel materials to look for light sub-GeV dark matter. In the second part, I will briefly describe the nonstandard cosmology of self-interacting neutrinos, how the latest data from Planck and ACT affect the model, and the current status of its link to the Hubble tension.

2023

Use of Bose symmetry to test symmetry violations

Date: 2023-11-06
Speaker: Prof. Rahul Sinha
Venue: Room no: 469 (Main campus)

Abstract

We will show how Bose symmetry in heavy flavour decays can be used to study violations of CP, CPT and SU(3) symmetries

Rapidity - dependent Jet vetoes at NNLL' + NNLO using SCET

Date: 2023-03-30
Speaker: Dr. Shireen Gangal
Venue: Room no: 469 (Main Campus)

Abstract

In this talk, I present resummed predictions for Higgs production via gluon fusion, and Drell-Yan production, in the framework of Soft Collinear effective theory (SCET). I introduce rapidity-dependent jet veto observables which provide a tight veto at central rapidities, gradually transitioning to a loose veto at forward rapidities. They divide the phase space into exclusive jet bins in a different way to the traditional jet veto observable pTjet. Using these rapidity-dependent jet vetoes, I present results for the 0-jet gluon-fusion Higgs cross section, and preliminary predictions for Drell-Yan at NLL’ + NLO and NNLL’ + NNLO. A significant reduction in perturbative uncertainty is observed going from NLL'+ NLO to NNLL'+ NNLO.

Reviving the sterile neutrino dark matter with neutrino secret self-interactions

Date: 2023-03-16
Speaker: Dr. Manibrata Sen
Venue: Online ---> https://bluejeans.com/512808345/1781

Abstract

Sterile neutrinos with masses around a few keV have been postulated to be viable dark matter candidates. This is, however, mostly in tension with various astrophysical observations, the most stringent being the X-ray bounds. In this talk, I would like to present a testable sterile neutrino dark matter production mechanism in the early Universe. The idea is to introduce a light scalar particle that mediates self-interactions among the Standard Model neutrinos. Such interactions enable the sterile neutrinos to be more efficiently produced in the early universe, thus alleviating the tensions and allowing the sterile neutrinos to be perfectly lucrative dark matter candidates. Such secret self-interactions can be tested in future neutrino experiments like DUNE. Apart from laboratory bounds, I will also discuss how these interactions can lead to exciting signatures in the early Universe as well as core-collapse supernovae.

Bosonization, Chiral L¨uttinger Liquid, Spin chain and Quantum Hall

Date: 2023-03-02
Speaker: Dr. Ankur Das
Venue: Room no: 469 (Main Campus)

Abstract

Bosonization is a general technique/formalism that helps us in taking 1D interacting fermion problem and turning them into effective non-interacting boson problem. I will talk in detail about the formalism, the assumptions, and the basics. I will go through also the mapping between operators and Hamiltonian in these two languages. I will discuss how they connect to the quantum Hall edge mode (Chiral L¨uttinger Liquid). Next, I will discuss the same for a simple spin chain model (XXZ spin chain) and how that can be mapped to L¨uttingerLiquid and neutral modes (spin wave). I will then discuss how interaction can play a role in detecting these neutral modes that we have discussed in our work [PRB 105, 165154 (2022)]

Topological Semimetals beyond regular

Date: 2023-03-01
Speaker: Dr. Ankur Das
Venue: Room no: 469 (Main Campus)

Abstract

Topological semimetals in three dimensions occur in mainly two variants, with the bands touching at point nodes (Weyl or Dirac semimetals) or touching at nodal lines in the Brillouin zone. However, there are new semimetals that challenge our notion, namely Nexus. Their existence needs lattice symmetry their classification needs an extra understanding of the system than usual. I will discuss how to understand the topology of Nexus Semimetals. On the other side while Weyl/Dirac semimetals can occur with internal symmetries only (such as time-reversal, charge conjugation, and possibly a product of the two, called chiral/sublattice symmetry), nodal line semimetals have been believed to require more symmetry, such as SU(2) spin rotation or crystalline symmetries. Though there has been discussion about possible topological classification of nodal line, how does in a generic the symmetry-constrained model they appear is not understood well. We show that chiral symmetry classes that are topologically nontrivial in three dimensions (namely class AIII, CII, DIII, and CI) always have a stable gapless phase, which is a topological nodal line semimetal even for the minimal model. We emphasize that no lattice or spin rotation symmetries are required for their robustness.

Su-Schrieffer-Hegger model with a non-orientable bulk: Union of topology and flat bands in one dimension

Date: 2023-02-28
Speaker: Bharathiganesh D
Venue: Room no: 469 (Main Campus)

Abstract

The Su-Schrieffer-Hegger model is the most simple but complete model of topological band insulators exhibiting features like bulk boundary correspondence. We investigate the possibility of the bulk in this model being a non-orientable manifold and consequences thereof. We find that in this case the topology of the SSH model is preserved along with the appearance of a doubly degenerate flat band at the Fermi level. We also find that there are states localised in the bulk along with the non-trivial edge modes in a finite chain. We will begin the talk with an introduction to band topology through the SSH model and continue to the case with non-orientable bulk.

Out-of-time-order correlators of nonlocal block-spin and random observables in integrable and nonintegrable spin chains

Date: 2023-02-23
Speaker: Mr. Rohit Kumar Shukla
Venue: Online ---> https://bluejeans.com/299910903/4490

Abstract

Out-of-time-order correlators (OTOC) in the Ising Floquet system, that can be both integrable and nonintegrable is studied. Instead of localized spin observables, we study contiguous symmetric blocks of spins or random operators localized on these blocks as observables. We find only power- law growth of OTOC in both integrable and nonintegrable regimes. In the non-integrable regime,beyond the scrambling time, there is an exponential saturation of the OTOC to values consistent with random matrix theory. This motivates the use of “pre-scrambled” random block operators as observables. A pure exponential saturation of OTOC in both integrable and nonintegrable systems is observed, without a scrambling phase. Averaging over random observables from the Gaussian unitary ensemble, the OTOC is found to be exactly same as the operator entanglement entropy, whose exponential saturation has been observed in previous studies of such spin-chains.

TPC #7: Measuring Entanglement in Electronic Interferometers

Date: 2023-02-07
Speaker: Prof. Yuval Gefen
Venue: K. R. Ramanathan Auditorium, PRL main campus

Abstract

This talk will rely on two fundamental themes of quantum physics: the statistics of identical particles, and entanglement. The former was thrust into the limelight, given the theoretical and experimental search for anyonic (fractional) statistics. The latter is a pillar of quantum mechanics: quantum entanglement prevents us from obtaining a full independent knowledge of a subsystem. Can one, theoretically and experimentally, focus on and isolate statistics-induced entanglement? Here I will address this question, addressing the case of fermions.

Dynamical Generation of Dark Matter and Electroweak Scales

Date: 2023-02-01
Speaker: Dr. Anish Ghoshal
Venue: Online ---> https://bluejeans.com/482088260/6256

Abstract

The Standard Model (SM) of particle physics suffers from the hierarchy problem which can be ameliorated if all the scales that we observe in nature are considered not to be fundamental but generated dynamically in nature. As examples, we will discuss freeze-out and freeze-in production of vector dark matter (DM) in a classically scale invariant theory, where the Standard Model (SM) is augmented with an extended gauge symmetries that are spontaneously broken due to the non-zero vacuum expectation value (VEV) of a scalar. Generating the SM Higgs mass at 1-loop level, it leaves only two parameters in the dark sector, namely, the DM mass mX and the gauge coupling gX as independent. For freeze-in, which require very feeble coupling to satisfy the relic, the scenario is testable in several light dark sector searches (e.g., in DUNE and in FASER-II) as well as direct detection probes in a complementary manner courtesy to the underlying scale invariance of the theory. We will show scenarios for neutrino-portal, axion-portal, Zprime-portal and HIggs-portal freeze in DM. In the second part of the talk we will briefly show how gravitational waves can be used to test freeze-in DM and complemented with laboratory signals.

The Phase puzzle of ν = 0 (charge neutrality) Graphene and Beyond

Date: 2023-01-19
Speaker: Dr. Ankur Das
Venue: Online ---> https://bluejeans.com/955982537/8037

Abstract

The true ground state of ν = 0 (charge neutrality) monolayer graphene quantum Hall has long been debated. Famously the symmetry of the monolayer graphene at ν = 0 (charge neutrality) was analyzed by J. Alicea and P. A. Fisher (PRB 2006), and canted anti-ferromagnet (CAF) was predicted by I. F. Herbut (PRB 2007). However, the complete picture of the Hamiltonian was missing until the seminal paper by M. Kharitonov (PRB 2012), which predicts a phase transition from a vanilla insulator (CAF) to a topological insulator Ferromagnetic phase (F) as one changes the Zeeman energy keeping the cyclotron energy fixed. This was later confirmed in the experiment by A. F. Young et al. (Nature 2014). Motivated by recent experiments (L. He et al. PRB 2019; Ali Yazdani et al. Science 2022; B. Sacepe et al. Nature 2022), we revisit this phase diagram. We show that, generically, in the regime of interest, there is a region of coexistence between magnetic and bond orders in the phase diagram. We demonstrate this result both in continuum and lattice models and argue that the coexistence phase naturally provides an explanation for unreconciled experimental observations on the quantum Hall effect in graphene. We further extend this idea to the whole phase diagram. This opens up many questions about different possibilities and new ideas, and possible mesoscopic experimental consequences.

A Type I+II seesaw model without Electroweak (EW) hierarchy

Date: 2023-01-06
Speaker: Debashis Pachhar
Venue: Room no: 469 (Main Campus)

Abstract

The Standard Model (SM) has passed all the precision tests in the past decades and provides the best description of the Electroweak (EW) and Strong interaction in nature. However there are motivations to tread beyond the SM, one of which is neutrino oscillations which established that neutrinos have small but non-zero mass. The most elegant mechanism to generate such small masses is the seesaw mechanism in which the smallness of neutrino masses is explained by introducing one or more heavy particles at a high scale. Two popular variants of these are the type-I and type-II models which require induction of singlet neutrinos and triplet Higgs fields respectively. Both these models are phenomenologically attractive but they suffer from the EW hierarchy problem. In this talk, I will explore the possibility of addressing this issue in the context of the type I+II seesaw model.

Deciphering the \sim 18 TeV photons from GRB 221009A

Date: 2023-01-05
Speaker: Prof. Sarira Sahu
Venue: Room no: 469 (Main Campus)

Abstract

On 9 October, 2022, an extremely powerful gamma-ray burst, GRB 221009A, was detected by several instruments. Despite being obstructed by the Milky Way galaxy, its afterglow outburst outshone all other GRBs seen before. LHAASO detected several thousands very high energy photons extending up to 18 TeV. Detection of such energetic photons are unexpected due to the large opacity of the Universe. It is possible that in the afterglow epoch the intrinsic very high energy photon flux from the source might have increased manifolds, which could compensate the attenuation by pair-production with the extragalactic background light. We propose such a scenario and show that very high energy photons can be observed on the Earth from the interaction of very high energy protons with the seed synchrotron photons in the external forward shock region of the GRB jet.

2022

SNS 2022: a summary

Date: 2022-12-30
Speaker: Prof. Navinder Singh
Venue: Room no: 469 (Main Campus)

Abstract

An informal discussion regarding the conference "Spectroscopies of Novel Superconductors (SNS 2022), 12th Dec to 16th Dec, Bangalore

Radiative inclusive semileptonic $B$ decays

Date: 2022-12-20
Speaker: Dayanand Mishra
Venue: Room no: 469

Abstract

Inclusive semileptonic decays are dominated by quark-level transitions and are found to be theoretically cleaner than the exclusive decays. We investigate how the on-shell hard photon impacts an inclusive process, ie we study the process $B \to X_u \ell \nu){\ell}\gamma$. We calculate the decay width for the said processes using the Cutkosky rules considering the operators up to dimension five in the heavy quark effective theory, and find that there are no new operators generated in the calculation of the decay width, and it leads to similar non-perturbative matrix elements as present in the decay width of $B\to X_u \ell \nu_{\ell} $. Hence, it provides a cleaner determination of the two non-perturbative parameters: $\lambda_1$ (which provides information about the average spatial momentum squared of the heavy quark), and $\lambda_2$ (the amount of color magnetic field produced by the light cloud at the position of the heavy quark).

From Quantum Optics to Bits and Pieces

Date: 2022-12-08
Speaker: Prof. Klaus Mølmer
Venue: Online ---> https://bluejeans.com/471795373/6057

Abstract

In this talk, I shall give a personally flavored account of the development of quantum optics starting with the simple, yet stunning, arguments applied by Roy Glauber to characterize temporal fluctuations in photo-detection signals. Such fluctuations can be signatures of non-classical properties, and the theory of photo-detection fueled the field of quantum optics with visions to prepare and apply a variety of quantum states of light and atomic light emitters in experiments. In the past decades, bits and pieces of solid-state materials were manufactured with high purity and precision, enabling observation of similar phenomena as we study with single atoms and photons in quantum optics. As a theorist I have worked with methods to describe the dynamics of open quantum systems, i.e., systems subject to interactions with their environment. I will show how these methods reintroduce, but with a plot twist, Niels Bohr’s quantum jumps in modern quantum physics. They also refine and elaborate on Glauber’s theories and while the original intent was to develop efficient theoretical and numerical methods that we can apply to quantum optics and solid-state bits and pieces, the same methods offer unique insights in physical dynamics and delightful encounters with the famous discussions between Niels Bohr and Albert Einstein on the interpretation of quantum theory.

On the spectrum of colour sextet scalars in realistic SO(10) GUT

Date: 2022-12-02
Speaker: Saurabh Shukla
Venue: Room no: 469 (Main Campus)

Abstract

Incorporation of the standard model Yukawa interactions in a grand unified theory (GUT) often predicts varieties of new scalars that couple to the fermions and lead to some novel observational effects. We assess such a possibility for the colour sextet diquark scalars within the renormalisable models based on SO(10) GUT. Computing explicitly their couplings with the quarks, we evaluate their contributions to the neutral meson-antimeson mixing and baryon number-violating processes like neutron-antineutron oscillation. Moreover, pointing out a possibility of generating the observed baryon asymmetry of the universe with these scalar sextets, we constrain the mass of the sextets respecting several other constraints in realistic SO(10) GUTs.

The case of itinerant magnetism in CaMn2Al10: self-consistent renormalisation (SCR) theory study

Date: 2022-11-29
Speaker: Bharathiganesh D.
Venue: Room no: 469 (Main Campus)

Abstract

CaMn2Al10 is a novel Manganese(Mn) based magnetic system which by conventional wisdom based on Mn-Mn distance should be a magnetic insulator. But experiments on CaMn2Al10 have revealed several signatures of itinerant magnetism in this system. The Self Consistent Renormalisation (SCR) theory of itinerant magnetism is a powerful and very reliable tool for the study of itinerant magnetism. Hence explaining the experimentally observed results through the SCR theory would make us decisively conclude that the system CaMn2Al10 is an itinerant magnet. The talk will cover a broad overview of the SCR theory followed by our calculations for CaMn2Al10 system.

Distinguishing third generation scalar leptoquarks using top quark polarization

Date: 2022-11-11
Speaker: Debashis Saha
Venue: Room no: 469 (Main Campus)

Abstract

We study the effect of NLO QCD correction merged with parton shower on the distribution of polarization observables that are associated to the top quark polarization and examine the prospect of identifying the genesis of scalar leptoquark by looking into their pair production at the LHC. We study various angular and energy variables at the NLO+PS accuracy to distinguish scalar leptoquarks originating from different models and do multivariate analysis with jet-substructure variables to reach a higher discovery potential.

Three way interplay of strong correlations, topology, and disorder in high temperature superconductors

Date: 2022-11-09
Speaker: Dr. Debmalya Chakraborty
Venue: Room no: 469 (Main Campus)

Abstract

One of the major challenges in condensed matter physics is to understand how many interacting electrons form different phases of matter. One such exotic phase of matter formed solely due to the presence of interactions is superconductivity. Ever since their discovery, superconductors have found applications across diverse fields of science starting from medical science to high energy and astrophysics, apart from the long sought after applications, like lossless power transmission and magnetic levitation trains. The practical applicability of superconductors depends heavily on the temperature regimes where they exhibit superconductivity. It is largely believed that electron-electron interactions hold a key in achieving high superconducting transition temperatures. Recently, superconductors have been combined with topology to obtain topological superconductors with potential applications for topological quantum computation. Real-world materials bring in disorder as an additional important component. Taking an example of a high temperature superconductor, I will show how three way interplay of strong electronic correlations, topology, and disorder generates a new quantum phase of matter: a fully gapped "phase crystal" state that breaks both translational and time reversal invariance, characterized by a modulation of the d-wave superconducting phase co-existing with a modulating extended s-wave superconducting order. In contrast to conventional wisdom, this phase crystal state is remarkably robust to omnipresent disorder, but only in the presence of strong correlations, thus giving a clear route to its experimental realization. I will further discuss how understanding the roles of interactions, topology, and disorder can not only answer various existing unsolved puzzles, but also provide pathways to discovering new materials with novel functionalities.

Key Aspects of EFTs

Date: 2022-10-19
Speaker: Dr. Jacky Kumar
Venue: Room no: 469 (Main Campus)

Abstract

In this talk, I will give details on the important technical aspects of the EFTs that are relevant for particle physics phenomenology and are often used in my work. In particular, I will discuss the advantages of using EFTs as compared to the full theory, EFTs at tree-level and 1-loop, matching, renormalization scheme dependence, renormalization group running (RGE) in the context of Delta F=1 and 2 flavour violating processes.

Explorations of physics at different scales

Date: 2022-10-18
Speaker: Dr. Jacky Kumar
Venue: Room no: 469 (Main Campus)

Abstract

In particle physics we try to probe nature at very small distance scales. Currently, the Standard Model (SM) of particle physics is the most successful model that can explain many of the observed phenomena. In 2012, the last missing piece of the SM, the Higgs Boson was discovered. Still, the SM can not be a complete theory of nature due to various reasons, so physics beyond it must exist. However, contrary to our expectations no other new particles have been found. Therefore, the scale of new physics (NP) might be much above the electroweak (EW) scale ~ 100 GeV. Interestingly, the scale hierarchies allow us to construct an effective field (EFT) which can be used to describe physics below a certain scale without knowing about the full ultraviolet theory, up to a certain approximation. Historically, the Weak effective theory (WET) was of great importance in the development of the SM. I will argue that, in the same way, the scale gap between the EW and the NP scale allows us to construct the EFTs which can serve as testing grounds for NP in the coming years, in a model independent fashion. In this context, I will highlight my recent work on the development of such EFTs, their phenomenological applications as well as computer tools to automate the phenomenological calculations using such EFTs.

TPC #5: Weber’s Electrodynamics

Date: 2022-09-29
Speaker: Prof. A. K. T. Assis
Venue: Online ---> https://osachapter.zoom.us/j/96972643322?pwd=VjBZdHNkTCtsVFM2YVdGZDk0QlRYdz09

Abstract

We present the origins of Weber’s electrodynamics (1846). Weber’s force depends not only on the distance between the interacting charges, but also on their relative velocity and relative acceleration. We discuss Ampère’s force between current elements and compare it with Grassmann-Biot-Savart’s law. We also compare Lorentz’s force with Weber’s force. We present Weber’s planetary model of the atom. It was developed before Rutherford’s experiments and Bohr’s model. In Weber’s planetary model, the positive nucleus is stabilized (or held together) by purely electrodynamic forces. According to Weber, when two positive charges are very close to one another, they behave as if they had a negative inertial mass, attracting one another instead of repelling each other. We discuss applications of Weber’s electrodynamics to superconductivity. We also present modern experiments and theoretical developments related to Weber’s electrodynamics.

A scotogenic $S3$ symmetric model for realistic neutrino mixing and generation of small yukawa couplings naturally from trans-Planckian asymptotic safety

Date: 2022-09-22
Speaker: Dr. Soumita Pramanick
Venue: Online ---> https://bluejeans.com/876239449/7355

Abstract

In the first segment of the talk I will discuss a scotogenic neutrino mass model at one-loop level based on discrete flavour symmetry $S3\times Z_2$. The model has two right-handed neutrinos. These two right-handed neutrinos when are maximally mixed, we can yield the form of the left-handed Majorana neutrino mass matrix with $\theta_{13}=0$ and $\theta_{23}=\pi/4$. Realistic mixing in agreement with the neutrino oscillation data i.e., non-zero $\theta_{13}$, deviation of $\theta_{23}$ from maximality and small corrections to solar mixing angle $\theta_{12}$ could be obtained by tweaking the maximal mixing between the two right-handed neutrino states by a small amount. The model has two $Z_2$ odd inert $SU(2)_L$ doublet scalars, the lightest among which can serve as a dark matter candidate. In the second segment of the talk we will focus on generation of arbitrarily small Yukawa couplings naturally due to the presence of a non-interactive infrared-attractive fixed point for gauge-Yukawa systems in trans-Planckian asymptotic safety framework. Together with the non-interactive infrared-attractive fixed point, more ultraviolet-attractive fixed points are also present in the system that ensure well-defined nature of the theory at infinitely high scale. This technology was used for a system of Yukawa couplings of the Standard Model extended by three right-handed neutrinos, for which asymptotically safe solutions for Dirac neutrinos satisfying the experimental constraints on neutrino masses and mixing for Normal Ordering were found. With the help of this general mechanism, feeble Yukawa interactions needed to produce the correct relic density via freeze-in for sterile-neutrino dark matter models can also be generated naturally.

Condensed dark matter with a Yukawa interaction

Date: 2022-09-20
Speaker: Dr. Raghuveer Garani
Venue: Online ---> https://bluejeans.com/298697694/1725

Abstract

I will discuss about the possible phases of a condensed dark matter (DM) candidate taken to be in the form of a fermion with a Yukawa coupling to a scalar particle, at zero temperature but at finite density. This theory essentially depends on only four parameters, the Yukawa coupling, the fermion mass, the scalar mediator mass, and the DM density. At low fermion densities we delimit the Bardeen-Cooper-Schrieffer (BCS), Bose-Einstein Condensate (BEC) and crossover phases as a function of model parameters using the notion of scattering length. I will further discuss in some detail the BCS phase by consistently including emergent effects such as the scalar density condensate and superfluid gaps. Within the mean field approximation, the consistent set of gap equations are derived, retaining their momentum dependence, and valid in both the non-relativistic and relativistic regimes. I will present numerical solutions to the set of gap equations, in particular when the mediator mass is smaller and larger than the DM mass. Finally, I will conclude with a few comments on the equation of state (EoS) and possible astrophysical implications for asymmetric DM.

TPC #4: Superconductivity: A phenomenon with many facets

Date: 2022-09-15
Speaker: Prof. Krishnendu Sengupta
Venue: oNLINE ---> https://osachapter.zoom.us/j/96615620484?pwd=RjE5aDBzaUh0VFpyVk9ESExTcEc1UT09

Abstract

In this talk, I shall provide a pedagogical introduction to the history of superconductivity. This will be followed by a discussion of unconventional superconductors and their phenomenology. I shall conclude with a brief discussion of unanswered questions and possible future directions.

TPC #3: Classical gravitational radiation from soft theorem.

Date: 2022-09-01
Speaker: Prof. Ashoke Sen
Venue: Online ---> https://osachapter.zoom.us/j/99386217848?pwd=NDJqdjFvdzZUd2xhelAxUFlPOENLQT09

Abstract

We shall discuss how some properties of scattering amplitudes in quantum gravity can be used to derive properties of classical gravitational radiation emitted during astrophysical processes.

Quantum Oscillations in Nodal-line semimetals

Date: 2022-08-30
Speaker: Dr. Satyaki Kar
Venue: Room no: 469 (Main Campus)

Abstract

Nodal line semimetals (NLSM) exhibit interesting quantum oscillation characteristics when acted upon by strong magnetic fields. We consider a NLSM continuum model to report the features of the Landau level spectra and the fluctuations in the Fermi level as the field in a direction perpendicular to the nodal plane is varied through. Based on the results on parallel magnetization, we demonstrate the growth of quantum oscillation with field strength as well as its constancy in period when plotted against 1/B. We find that the density of states which show series of peaks in succession, witness bifurcation of those peaks due to Zeeman effect. For field normal to nodal plane, such bifurcations are discernible only if the electron effective mass is considerably smaller than its free value, which usually happens in these systems. Though a reduced effective mass m∗ causes the Zeeman splitting to become small compared to Landau level spacings, experimental results indicate a manyfold increase in the Lande g factor which again amplifies the Zeeman contribution. Interestingly, topologically nontrivial oscillations are witnessed at low energies when the magnetic field lies in the nodal plane. There the density of state peaks do not repeat periodically with energy anymore. The spectra become more spread out and the Zeeman splittings become less prominent. We find the low energy topological regime, that appears with such in-plane field set up, to shrink further with reduced m∗ values. However, such topological regime can be stretched out in case there are smaller Fermi velocities for electrons in the direction normal to the nodal plane. Moreover, an oscillatory field variation, as opposed to a steady one, has interesting impact on the quantum oscillation phenomena with the Landau tubes crossing the Fermi surface extremally two times per cycle. With proper parameters chosen, one can engineer topological transitions to occur periodically in such systems as an in-plane oscillating field is swept through its cycles.

Phase transitions and critical phenomena in a disordered Potts model

Date: 2022-08-29
Speaker: Dr. Manoj Kumar
Venue: Online ---> https://bluejeans.com/709008545/1460

Abstract

In this talk, I’ll speak about the phase transitions and critical features in a three-state random field Potts model (RFPM) in three dimensions. Considering a universal feature that the phase transition in such models is governed by a zero-temperature random fixed point, we target the problem by determining the ground states at temperature T = 0. Finding ground states however in RFPM is known to be NP-hard. We make use of a computationally efficient graph cut algorithm to determine excellent approximate ground states in P time. From such states, various quantities like magnetization, Binder-cumulant, specific heat, susceptibility, are evaluated and extrapolated in the limit of quasi-exact ground states. These results are obtained for different system sizes and an extensive finite-size scaling approach is implemented to estimate the critical point and the exponents that characterize the singular behavior near the transition.

TPC #2: Many-body Localization: Recent Advancements and Puzzles

Date: 2022-08-18
Speaker: Prof. Arti Garg
Venue: Online --> https://bluejeans.com/954548701/2310

Abstract

The physics of Anderson localization in non-interacting disordered quantum systems has been a cornerstone of condensed matter theory. Turning on interactions in these disordered systems results in the many-body localized (MBL) phase where the system lacks transport up to a finite temperature. In this talk I will review recent advancements in the field of MBL, both, on theoretical and experimental sides followed up by the open questions and problems. I will also mention some of our recent works on MBL which have helped to characterize the MBL phase and resolved the long standing issue about the stability of the MBL phase in the presence of long range interactions.

Self-interacting dark matter and related phenomenologies

Date: 2022-08-17
Speaker: Dr. Manoranjan Dutta
Venue: Online --> https://bluejeans.com/954548701/2310

Abstract

The Standard Model of Cosmology or the ΛCDM model, where DM is postulated to be cold and collisionless is in excellent agreement with the large-scale structures of the Universe. However, at small scales (most prominently at the scale of dwarf galaxies), there are several discrepancies between the astrophysical observations and the predictions of the ΛCDM model, leading to small-scale anomalies such as `cusp-core problem', `missing satellite problem' and `too-big-to-fail problem'. To alleviate these small-scale anomalies, self-interacting dark matter (SIDM) was proposed in 2000. SIDM particles have very large self-interaction among themselves with a scattering cross-section of O(10-24 cm2/GeV), which is many orders of magnitude larger than the typical WIMP cross-section of O(10-38 cm2/GeV). Moreover, the favoured cross-section scale decreases gradually from dwarf to cluster scale and eventually matches with ΛCDM predictions at a large scale, hinting towards a velocity-dependent self-interaction cross-section. In the light of these inadequacies of the ΛCDM model and since the Standard Model (SM) of particle physics fails to provide a viable DM candidate, I will discuss a few beyond the Standard Model (BSM) scenarios capable of explaining SIDM and related phenomenologies like the tiny neutrino mass. I will discuss both elastic and inelastic self-scattering of DM via a light mediator through Yukawa-type potentials, while neutrino phenomenology involves the popular seesaw variants.

Radiatively generated fermion mass hierarchy from flavour non-universal gauge symmetries

Date: 2022-08-11
Speaker: Gurucharan Mohanta
Venue: Room no: 469 (Main camp)

Abstract

A framework based on a class of abelian gauge symmetries is proposed in which the masses of only the third generation quarks and leptons arise at the tree level. The fermions of the first and second families receive their masses through radiative corrections induced by the new gauge bosons in the loops. It is shown that the class of abelian symmetries which can viably implement this mechanism are flavour non-universal in nature. Taking the all-fermion generalization of the well-known leptonic $L_\mu-L_\tau$ and $L_e - L_\mu$ symmetries, we construct an explicit renormalizable model based on two $U(1)$ which is shown to reproduce the observed fermion mass spectrum of the Standard Model. The first and second generation fermion masses are loop suppressed while the hierarchy between these two generations results from a gap between the masses of two vector bosons of the extended gauge symmetries. Several phenomenological aspects of the flavourful new physics are discussed and lower limits on the masses of the vector bosons are derived.

TPC #1: Evolution of Modern Science in India

Date: 2022-08-04
Speaker: Prof. Sreerup Raychaudhuri
Venue: Online --> https://osachapter.zoom.us/j/96118620386?pwd=cnNZcUJyekZTR3JJOEc4aExQTFQ2UT09

Abstract

In this non-technical talk, the history and evolution of modern science in India will be broadly surveyed. After a brief introduction, the introduction of scientific processes by the British will be mentioned, and followed by a description of the spread of western education in India. The contributions of pioneering Indian scientists in the colonial period will then be described. Finally, the growth of major scientific and technological institutions in post-independence India will be outlined.

Improved Constraints on Effective Top Quark Interactions using Edge Convolution Networks

Date: 2022-07-14
Speaker: Dr. Akanksha Bhardwaj
Venue: Room No. 469 (Main Campus)

Abstract

In this talk, we will discuss the potential of Graph Neural (GNNs) to improve the performance of high-dimensional effective field theory parameter fits collider data beyond traditional rectangular cut-based differential distribution analyses. We will focus on a SMEFT analysis of pp→tt production, including top decays, where the linear effective field deformation is parametrised by thirteen independent Wilson coefficients. The application of GNNs allows us to condense the multidimensional phase space information available for the discrimination of BSM effects from the SM expectation by considering all available final state correlations directly. The number of contributing new physics couplings very quickly leads to statistical limitations when the GNN output is directly employed as an EFT discrimination tool. However, a selection based on minimising the SM contribution enhances the fit's sensitivity when reflected as a (non-rectangular) selection on the inclusive data samples that are typically employed when looking for non-resonant deviations from the SM by means of differential distributions.

Experimental and Theoretical Study of Non-Linear Optical Crystals

Date: 2022-07-01
Speaker: Dr. Mitesh Solanki
Venue: Online ---> https://bluejeans.com/108520645

Abstract

One of the most often used nonlinear optical materials is Potassium Dihydrogen Phosphate (KDP). Growth in slow solvent evaporation at room temperature has resulted in high-quality Alkali (Li, Rb and Cs) doped KDP crystals grown. When studying the structure of formed crystals, it was discovered that they were single-phasic and had only modest variations in their unit cell characteristics. During the Retvield refining, the role of dopant was studied. This technique was used to study the linear optical characteristics of formed crystals, such as the optical transparency energy band gap; reflectance; extinction coefficient; refractive index; etc. When doping KDP crystals, the Kurtz and Perry powder NLO approach was used to investigate the nonlinear optical improvement that occurred. It was used to conduct an a.c. electrical investigation of generated crystals. The Generalized Gradient Approximation pseudopotential approach has been used in the theoretical investigation like band structure, density of state elastic constant, optical properties and phonon dynamics of single crystals produced.

Cwebs beyond three loops in multiparton amplitudes

Date: 2022-06-23
Speaker: Mr. Sourav Pal
Venue: Online

Abstract

The correlators of Wilson-line operators are fundamental objects for the study of the infrared properties in QCD and other non-abelian gauge theories. In perturbation theory, they are known to exponentiate, and their logarithm can be organized in terms of collections of Feynman diagrams called webs. In this talk, I will discuss some recent results regarding their organization at higher perturbative orders, determination of the colour structures that contribute to the soft anomalous dimension, and a new method of constructing the web mixing matrices.

Beyond Standard Model : A left-right theory approach

Date: 2022-06-16
Speaker: Dr. Chayan Majumdar
Venue: Online --> https://bluejeans.com/495767101/4803

Abstract

In spite of being a successful theory, the Standard Model (SM) has several shortcomings. All these limitations of the SM give a clear hint of Beyond SM (BSM) physics and Left-Right (LR) theories are one of the successful BSM scenarios to provide a unified explanation to the origin of small neutrino mass and low-energy parity violation in weak phenomenology. The spontaneous breakdown of LR symmetry to SM can be achieved via the vacuum expectation values (vevs) of either (i) bidoublet + triplet Higgs, or (ii) bidoublet + doublet Higgs or (iii) combination of both (i) and (ii). We have considered such several variants of Higgs sectors in LR symmetry and studied certain phenomenological and cosmological signatures of these frameworks. Moreover, another approach to conventional LRSM, aka, ALRM can evade unavoidable FCNC constraints naturally. We have explored one of such ALRMs where we have studied the possibility of having significant contribution to neutrinoless double beta decay as well as low-scale leptogenesis.

Disorder, strong correlations and unconventional superconductors

Date: 2022-06-14
Speaker: Dr. Vivek Mishra
Venue: Ground floor lecture hall

Abstract

Unconventional superconductivity is one of the key areas of research for past several decades, either due to high transition temperatures or due to exotic superconducting states with novel topological properties. Most of the unconventional superconductors are intrinsically dirty. They carry lots of impurities, therefore, relevant to this discussion is disorder that always exists in these systems. Here I will review the seminal work by Abrikosov and Gorkov that is widely used to understand the disorder effects in superconductors. I will then discuss the limitation of the Abrikosov-Gorkov theory in the case of electronic pairing. I will present some of my new results showing the effect of strong correlation on impurity scattering in d-wave superconductors that are relevant for cuprates. I will also discuss the implications of realistic impurities

Disorder, strong correlations and unconventional superconductors

Date: 2022-04-21
Speaker: Dr. Vivek Mishra
Venue: Online --> https://bluejeans.com/758381390/4420

Abstract

Unconventional superconductivity is one of the key areas of research for past several decades, either due to high transition temperatures or due to exotic superconducting states with novel topological properties. Most of the unconventional superconductors are intrinsically dirty. They carry lots of impurities, therefore, relevant to this discussion is disorder that always exists in these systems. Here I will review the seminal work by Abrikosov and Gorkov that is widely used to understand the disorder effects in superconductors. I will then discuss the limitation of the Abrikosov-Gorkov theory in the case of electronic pairing. I will present some of my new results showing the effect of strong correlation on impurity scattering in d-wave superconductors that are relevant for cuprates. I will also discuss the implications of realistic impurities.

Chiral limit of QCD: interests and relevance

Date: 2022-04-18
Speaker: Dr. Anirban Lahiri
Venue: Online --> https://bluejeans.com/478390705/7319

Abstract

I would like to start with the features of the phase diagram of QCD in the physical world, where the pion has mass equal to its PDG value. Next I want to add one dimension in that diagram in terms of light quark masses and discuss how the previously discussed phase plane for the physical world is embedded in a more global structure and I will discuss the various aspects of this global phase diagram. After setting the stage I would like to focus on the behavior of the Polyakov loop towards the chiral limit of QCD. On contrary to the folklore that the Polyakov loop can be treated as a pseudo-order parameter of deconfinement for finite quark masses, we showed that the Polyakov loop is essentially sensitive to the chiral transition for physical and smaller than physical quark masses and behave as an energy-like observable w.r.t. the chiral phase transition.

Exploring strongly interacting matter with small quark masses

Date: 2022-04-07
Speaker: Dr. Anirban Lahiri
Venue: Online --> https://bluejeans.com/271773288/2243

Abstract

Exploration of the phases of the strongly interacting matter under extreme conditions has been a topic of immense discussion over the last decades. Attempts have been made both from theoretical and experimental workfronts like ALICE@LHC, STAR@RHIC and CBM@FAIR and plenty of others, to understand the phases and transitions between them. Chiral symmetry breaking and confinement are the two most important effects in the non-perturbative domain of Quantum ChromoDynamics (QCD) which is the field theoretic description of the strongly interacting matter, in the theoretical perspective. In this talk I will discuss the features of QCD towards the vanishing value of light quark masses, the so-called chiral limit. Starting with an introduction to the QCD phases in the physical world I will continue with some new results towards the chiral limit calculated using the lattice framework of QCD and various salient features related to the critical behavior that can be realized through our latest calculations.

Controllable long-range entanglement in a lossy qubit array

Date: 2022-04-04
Speaker: Dr. Shovan Dutta
Venue: Online --> https://bluejeans.com/242229952/8151

Abstract

Environmental noise typically drives a quantum system to a unique steady state with little quantum correlations, which is a major obstacle for quantum information processing. I will talk about a simple experimental setting of an array of two-level systems with localised environmental noise that has multiple highly coherent steady states, including maximally-entangled states of nonlocal (Bell) pairs. Such states originate from a hidden symmetry that conserves these pairs over long distances, leading to controllable long-range entanglement. I will discuss how to selectively prepare and observe these states in present-day many-body atomic/photonic setups.

Lower moments of nucleon parton distribution functions (PDFs) in lattice QCD

Date: 2022-03-31
Speaker: Dr. Santanu Mondal
Venue: Online --> https://bluejeans.com/206075327/5345

Abstract

In this talk, I will first introduce parton distribution functions and discuss their phenomenological importance. Then I will describe our recent first-principle calculations using lattice QCD (Phys. Rev. D102 (2020) no.5, 054512 and JHEP 04 (2021) 044, JHEP 21 (2020) 004) of the first x-moment of nucleon isovector polarized, unpolarized and transversity distributions. We use the standard method for the calculation of these moments (via matrix elements of twist two operators) and carry out a detailed analysis of the sources of systematic uncertainty, in particular of excited state contributions. Finally, I will describe my future plans in this direction and in a different direction (composite Higgs models on the lattice).

Probing the First Billion Years of our Universe with 21-cm radiation from neutral hydrogen.

Date: 2022-03-24
Speaker: Dr. Raghunath Ghara
Venue: Online --> https://bluejeans.com/942367125/7939

Abstract

The redshifted 21-cm signal from the intergalactic medium (IGM) neutral hydrogen is the most promising probe of the Epoch of Reionization. It has the ability to reveal many of the unknown facts about this epoch such as properties of the early sources of radiation, thermal and ionization states of the IGM. Radio telescopes such as LOFAR, MWA, HERA are providing stronger upper limits on the 21-cm power spectrum. I will be talking about this probe and how these measurements are used to infer the states of the IGM as well as the properties of the first sources that formed during that period.

Disordered Bose Hubbard model and percolation analysis

Date: 2022-02-17
Speaker: Hrushikesh Sable
Venue: Online --> https://bluejeans.com/174262927/0866

Abstract

The interplay between disorder and interactions in many-body quantum systems leads to novel quantum phases. The Bose-Hubbard model (BHM) is a prototypical model to describe the physics of ultracold atoms in optical lattices. In the context of the BHM, the introduction of disorder results in a Bose-glass (BG) phase, apart from the usual Mott Insulator and superfluid (SF) phases. In this talk, we shall discuss the equilibrium phase diagram and the properties of these quantum phases. In particular, we shall focus on the critical properties of the BG-SF phase transition. We shall demonstrate the methods of percolation theory to locate the phase boundary of the BG-SF transition.

Precision Prediction of Higgs cross section and New Physics signals in B-decays

Date: 2022-01-06
Speaker: Dr. Shireen Gangal
Venue: Online --> https://bluejeans.com/386832560/8794

Abstract

In the first part of my talk, I will discuss precision predictions of Higgs production cross section via gluon fusion, with a veto imposed on additional jets using rapidity-dependent jet vetoes. These jet veto observables provide a tight veto at central rapidity, gradually transitioning to a loose veto at forward rapidities. I will present predictions for the Higgs+0-jet cross section using these rapidity-dependent jet vetoes at NNLL' + NNLO accuracy within the framework of Soft Collinear Effective Theory. In the second part, I will discuss the intriguing hints of lepton flavour universality violation that have accumulated in B-meson decays. In a recent re-analysis of 2018 Belle data, it was found that the lepton forward-backward asymmetry of B→ D* μν vs B→ D* eν decays is in tension with the SM prediction. I will present results of a global fit to b → c l ν data which show that a new physics scenario with scalar and tensor operators can significantly reduce this tension.

2021

Quest for New Physics with the ratio of CKM elements

Date: 2021-12-23
Speaker: Dayanand Mishra
Venue: Online --> https://bluejeans.com/231422431/5680

Abstract

The CKM elements $|V_{ub}|$ and $|V_{cb}|$ show a discrepancy between the exclusive and inclusive determinations. These determinations are however masked with hadronic and other uncertainties, and thus can’t be unambiguously taken as implying new physics. In this talk, we consider a new observable: the ratio of these two CKM elements, $R_{V} ≡ \frac{|V_{ub}|}{|V_{cb}|}$, which is found to receive negligible corrections due to hadronic as well as QED effects. It is observed that the $R_{V}$ as constructed from exclusive determinations of $|V_{ub}|$ and $|V_{cb}|$ agrees quite well with that constructed from the inclusive determinations of these CKM elements. Hence, we show that $R_{V}$ is a cleaner observable, and can serve as an excellent tool for the test of the Standard Model.

Energy-weighted Message-Passing Networks

Date: 2021-10-28
Speaker: Ng. Vishal Singh
Venue: Online --> https://bluejeans.com/626648208/1962

Abstract

Hadronic signals of new-physics origin at the Large Hadron Collider can remain hidden within the copiously produced hadronic jets. Unveiling such signatures requires highly performant deep-learning algorithms. In this talk, I will discuss the construction of a class of Graph Neural Networks (GNN) in the message-passing formalism that makes the network output infra-red and collinear (IRC) safe, an important criterion satisfied within perturbative QCD calculations. Including IRC safety of the network output as a requirement in the construction of the GNN improves its explainability and robustness against theoretical uncertainties in the data. We generalise Energy Flow Networks (EFN), an IRC safe deep-learning algorithm on a point cloud, defining energy weighted local and global readouts on GNNs. Applying the simplest of such networks to identify top quarks, W bosons and quark/gluon jets, we find that it outperforms state-of-the-art EFNs.

The overproduction of truth: from passion to market

Date: 2021-09-30
Speaker: Dr. Navinder Singh
Venue: Online --> https://bluejeans.com/682044853/7622

Abstract

In the 19th and first half of the 20th century, the number of scientific discoveries scales as linear with the number of scientific publications. But from the second half of the 20th century, the number of publications far exceeds the number of impactful discoveries. Does an exponentially growing number of publications indicate an element of pathological research? Pressure to publish a large number of papers has led to the phenomena of overproduction, unnecessary fragmentation, overselling, and deliberate obfuscation of scientific results so as to sell and oversell. This also has led to the phenomenon of predatory journals (pay and publish), and clever plagiarism. This is harming the healthy scientific culture of passion driven research. This is an urgent problem which needs attention of the whole of the scientific community. Ways to mitigate these grave problems are discussed.

Electronic transport due to magnetic scattering mechanisms: the Memory Function Approach

Date: 2021-09-23
Speaker: Komal Kumari
Venue: Online --> https://bluejeans.com/116525241/1376

Abstract

I present the theoretical analysis of electronic transport in magnetic materials. In these materials the electrical resistivity originates from electron magnetic spin fluctuation scattering (alongwith electron-phonon scattering). I use the Kondo-lattice Hamiltonian to investigate the temperature dependence of resistivity in heavy fermion materials. Computations of resistivity are performed using the Memory function formalism. I also explore the behaviour of resistivity in two dimensional ferromagnets tuned near to their magnetic instability. In this case, the calculations are performed using the random phase approximation for the dynamical susceptibility, from which the resistivity is computed. Our calculations are applicable to weakly ferromagnetic systems and to heavy fermion materials.

The anatomy of the multi-lepton anomalies at the LHC and a candidate for a singlet scalar

Date: 2021-09-20
Speaker: Prof. Bruce Mellado
Venue: Online --> https://bluejeans.com/706821627/1905

Abstract

In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC is given. These include the excess production of opposite sign leptons with and without b-quarks, including a corner of the phase-space with a full hadronic jet veto; same sign leptons with and without b-quarks; three leptons with and without b-quarks, including also the presence of a $Z$. Excesses emerge in corners of the phase space where a range of SM processes dominate, indicating that the potential mismodeling of a particular SM process is unlikely to explain them. A procedure is implemented that avoids parameter tuning or scanning the phase-space in order to nullify potential look-else-where effects or selection biases. The internal consistency of these anomalies and their interpretation in the framework of a simplified model are presented. Motivated by the multi-lepton anomalies, a search for narrow resonances with $S\rightarrow\gamma\gamma, Z\gamma$ in association with light jets, $b$-jets or missing transverse energy is performed. The maximum local (global) significance is achieved for $m_S=151.5$\,GeV with 5.1$\sigma$ (4.8$\sigma$).

Synergy of Neutrino and Dark matter at the advanced particle detector

Date: 2021-09-16
Speaker: Animesh Chatterjee
Venue: Online --> https://bluejeans.com/165045009/1320

Abstract

The predictions of the standard model (SM) have been verified to a remarkable degree of accuracy, but there are still some unanswered questions. Neutrino and dark matter offer great potential for digging out physics beyond the standard model. With the advent of a new generation of advanced neutrino experiments, it is timely to explore physics topics beyond the standard neutrino oscillation. Dark matter phenomenology is turning to more exotic models, neutrino detectors are sensitive to some of those. In this talk, I will discuss the opportunity to explore physics beyond the standard neutrino oscillations, as well as how one can search for dark matter using the same existing setup for neutrino experiment.

Grand Unification: Proton Lifetime, Topological Defects, Inflation and Gravity Waves

Date: 2021-08-26
Speaker: Rinku Maji
Venue: Online --> https://bluejeans.com/954481929/5618

Abstract

The Super-Kamiokande (Super-K) experiment sets sacrosanct bounds on the partial lifetime ($\tau$) of the proton decay for different channels, e.g., $\tau(p\to e^+ \pi^0) > 1.6\times 10^{34}$ years which is the most relevant channel to test the viability of the nonsupersymmetric GUTs. The GUTs based on the gauge groups $SO(10)$ and $E(6)$ are broken to the SM spontaneously through one and two intermediate gauge symmetries with the manifestation of the left-right symmetry at least at a single intermediate stage and the proton lifetime for these breaking chains has been computed. The impact of the threshold corrections after integrating out the heavy fields at the breaking scales alters the running of the gauge couplings, which eventually keeps many GUTs off the Super-K bound. Effect of dimension-$5$ operators improves the proton lifetime for specific breaking paths. The stable topological defects can be inflated away if the universe undergoes a sufficient number of $e$-foldings after these defects are formed. We have studied the limit on such breaking scales under the lamppost of GUT inflation using the Coleman-Weinberg potential of a GUT singlet inflaton. We will discuss the generation and subsequent evolution of magnetic monopoles and cosmic strings, as well as the emission of gravity waves from the decaying string loops.

Realizing flavored leptogenesis: a reappraisal through special kinds of orthogonal matrices

Date: 2021-08-23
Speaker: Nimmala Narendra
Venue: Online --> https://bluejeans.com/846326717/5120

Abstract

The parameterization proposed by Casas and Ibarra in the year 2001 has shown a promising role in the extraction of neutrino Yukawa coupling which is a basic ingredient of the seesaw mechanism generating neutrino mass. We pay special attention in establishing the crucial role of the Casas-Ibarra (CI) parameterization in presence of two different orthogonal matrices, R = O e^{iA} and R = O e^{A} in order to investigate flavored leptogenesis. In the light of these two choices of the orthogonal matrix, we examine the connection between the low energy and high energy CP violations along with certain interesting predictions on the low energy parameters namely, the lightest neutrino mass and the Dirac CP phase (δ). Considering the right-handed neutrino (RHN) mass window to be 10^8 GeV, we show that Dirac phase leptogenesis is possible with the choices of these two orthogonal matrices. We choose a nearly degenerate spectrum for the RHN masses for having a successful leptogenesis. We also emphasize on presenting a range of the matrix elements of the skew-symmetric matrix A. The results obtained in the present analysis underline the importance of understanding the status of CP violation in the low energy sector. We also discuss the phenomenological implications of these two case studies in the context of LFV considering the µ -> eγ decay process.

Importance of second oscillation maxima in probing invisible neutrino decay

Date: 2021-08-19
Speaker: Kaustav Chakraborty
Venue: Online --> https://bluejeans.com/116266679/4331

Abstract

The constraints on invisible neutrino decay can come from future planned/proposed long baseline experiments - T2HK/T2HKK and ESSνSB. The T2HKK and ESSνSB experiments are both designed to have energy peak near the second-oscillation maximum of Pμe while T2HK has the energy peak at the first oscillation maximum of Pμe. We perform a full three flavour study using matter effect and obtain the sensitivity to τ3/m3 for these experiments. In particular, we investigate how the experiments at first and second oscillation maximum fare in presence of neutrino decay. We also study the important factors on which the measurement of θ23 can depend in presence of decay. We have found that in presence of decay, the overall octant sensitivity is enhanced. This can be attributed to the octant sensitive contribution coming from the disappearance channel (Pμμ) in presence of neutrino decay.

Exploring the signature of non standard interactions in long baseline neutrino experiments

Date: 2021-08-04
Speaker: Supriya Pan
Venue: Online --> https://bluejeans.com/239534349/0818

Abstract

We have ventured a lot into the paradigm of neutrino oscillation, governed by mass squared differences between neutrino states and mixing. Most of these parameters are now well determined and for the measurement of the remaining parameters many high statistics experiments are planned. These experiments also provide the opportunity to explore imprint of of new physics in neutrino oscillations. We have studied the effect of non- standard interaction on neutrino oscillation probabilities during their propagation through Earth's matter. We focus on the conversion probability of muon to tau neutrinos. In the simple two-generation case the probability $P_{\mu\tau}$ is not affected by interactions of neutrinos in matter. But for three generation case at baselines of the order of 9000 km there are matter effects affecting this channel. This is considered a genuine three flavour effect. We study how the presence of non-standard interaction alters the $P_{\mu\tau}$ probability at these baselines. We observe large deviations from standard matter effect , which indicates presence of new physics to be probed in upcoming experiments.

Probing the inert doublet model in next-to-leading order QCD at the LHC

Date: 2021-08-04
Speaker: Anupam Ghosh
Venue: Online --> https://bluejeans.com/536192538/2721

Abstract

LO analysis of the IDM model in the hierarchical mass spectrum is well studied. The IDM model gives a viable dark matter (DM), and hierarchy mass spectrum means DM mass is low and heavy scalars have the mass of the order 100 GeV larger than DM. We will take one order alpha_s correction of the IDM Lagrangian along with gluon gluon Higgs effective Lagrangian. When a pair of pseudoscalars is produced, the k-factor in all the benchmark points is greater than 1.7. Pair of DM annihilates into SM particles through Higgs boson mediator is the only annihilation channel in low DM mass regime, and this channel has a k-factor of 1.86. So it is essential to include the NLO correction to get an actual description. In this study, after taking one order correction of the total Lagrangian, we study the jets+MET signal. Di-fatjet+MET signal looked previously at LO accuracy. We explore this difatjet +MET signal with NLO accuracy and shown that if one considers only LO, then 1J_V + MET signals are overproduced, and 2J_V + MET is underestimated. With NLO accuracy, we show that the significance improves in the cut-based analysis.

Non-Radial Oscillation modes in Hybrid Stars: Consequence of Mixed Phase

Date: 2021-08-03
Speaker: Deepak Kumar
Venue: Online --> https://bluejeans.com/678749840/7882

Abstract

Neutron stars are interesting laboratories to study matter at high densities. At high densities (of the order of 3 to 4 times nuclear matter density), the normal confined nuclear matter is expected to undergo the phase transition to deconfined quark matter. It is expected that neutron stars might contain deconfined quark matter in the inner core and nuclear matter in the outer core. In this talk, I will discuss the phase transition from nuclear matter to quark matter at high densities with a possibility of a mixed phase. I will also discuss the consequences of the mixed phase in the core of neutron star/hybrid star in the context of mass radius relation. Finally I will present some results on the non-radial oscillation modes in such stars.

Singlet Doublet Freeze-in dark matter in the presence of (non-)standard cosmology

Date: 2021-08-02
Speaker: Sudipta Show
Venue: Online --> https://bluejeans.com/593904063/3558

Abstract

Decades of null results from different direct detection experiments for dark matter keep suggesting that the weakly interacting massive particle(WIMP) paradigm may need a relook for the theory of particle dark matter. The non-thermally produced freeze-in dark matter is an exciting and alternative proposal. It naturally explains the non-observation of any signature because of its feeble interaction with the standard model particles. We consider a simple extension of the standard model with a pair of fermions, one singlet, and doublet to incorporate dark matter. We discuss the freeze-in production of dark matter in the context of the singlet-doublet model. Also, we talk about the effect of the fast expansion of the Universe on the dark matter phenomenology.

Radiative Leptonic Decays of Kaons and Light Cone Sum Rules

Date: 2021-07-30
Speaker: Anshika Bansal
Venue: Online --> https://bluejeans.com/824628878/0559

Abstract

The leptonic decays of pseudoscalar mesons (kaon, pion, etc) are essential ingredients for extraction of CKM matrix elements. In the standard model, these decays are helicity suppressed. The helicity suppression can be lifted by considering the radiative leptonic decays which show an interesting pattern for the case of kaons. The radiative decay also helps in understanding the dynamics of strong interaction via two transition form factors (FFs): vector (V) and the axial vector (A) FF. The study of these FFs became more interesting after a recent publication (arXiv: hep-ph/2012.02120) which has reported significant differences between the lattice and experimental results for values of (V+A) and (V-A). We have attempted to compute these FFs (in particular for $K^- \rightarrow \ell^- \nu_\ell \gamma$) in the framework of light cone sum rules (LCSR) upto twist-4 accuracy. In this talk, I will discuss the computation of these FF in LCSR and the challenges involved along with the preliminary results.

Self Consistent Renormalisation (SCR) Theory of Itinerant Magnetism

Date: 2021-07-29
Speaker: Bharathiganesh D.
Venue: Online --> https://bluejeans.com/126889001/4341

Abstract

Understanding Itinerant electron magnetism has always been a matter of interest as it holds the key for understanding magnetism in metals like Iron, Nickel Cadmium. Recently there has been synthesis of many heavy Fermion compounds and anti ferromagnets which are expected to be itinerant magnets and this has kindled the interest further in the subject. Self Consistent Renormalisation (SCR) theory is the best among the available theories for itinerant magnetism, whose predictions agree well with experiments. In this talk we will discuss the SCR theory in detail. We will also discuss the results of numerical calculations that we have obtained in order to show the level of accuracy to which the predictions of SCR theory hold true in the regime of itinerant magnetism.

Fractional Quantum Hall states on Optical Lattices

Date: 2021-07-28
Speaker: Deepak Gaur
Venue: Online --> https://bluejeans.com/536889561/0706

Abstract

The studies pertaining to the Quantum Hall (QH) effect and QH states constitute an active area of research. In condensed matter systems, the observation of the QH states is difficult, as they require very high magnetic fields (~ 10 Tesla). Instead, ultracold atoms in optical lattices are useful systems as synthetic magnetic fields of high magnitude can be generated in these systems. In this talk, we shall discuss about the study of the QH effect and realization of the synthetic magnetic field in a system of charge neutral bosons in optical lattices. We shall also discuss various properties of the QH states and in particular the calculation of the Many body Chern number which characterises the topological order of QH states.

Higher order precision calculations in QCD and N=4 SYM

Date: 2021-07-26
Speaker: Dr. Maguni Mahakhud
Venue: Online --> https://bluejeans.com/790912493/3405

Abstract

As the experimental accuracy of different observables is increasing day by day at different colliders, precise theoretical predictions become very important. The Large Hadron Collider (LHC) plays a very important role in confirming the Standard Model (SM) of Particle Physics and constraining Beyond Standard Model (BSM) physics. Since LHC is a hadron collider, Quantum Chromodynamics (QCD) corrections are very important in calculating different observables. These calculations become very difficult due to the increasing number of loops and external legs. So far, many techniques have been developed to handle these difficulties and many more are in the developmental process. I will explain some of such techniques used in calculating higher order corrections in this talk. Also these QCD amplitudes contain universal infrared divergence structures and N=4 SYM often captures large chunks of full QCD computations. The high symmetry of N=4 SYM sometimes helps to get a cleaner view on fundamental features that may remain hidden in QCD for its additional complexity. Similarities of QCD observables with N=4 SYM could be the indications to undiscovered hidden symmetries. I will discuss on such universal structures of QCD and N=4 SYM amplitudes.

Self Consistent Renormalization (SCR) Theory of Itinerant Magnetism

Date: 2021-07-19
Speaker: Dr. Akariti Sharma
Venue: Online --> https://bluejeans.com/162793618/8011

Abstract

We theoretically investigate the effects of electron correlation on itinerant magnetism by using the Self Consistent Renormalization (SCR) theory. It is found that this theory is quite successful in approximating the Curie-Weiss like behavior of the temperature dependence of the magnetic susceptibilities above the Curie temperature Tc: widely observed in ferromagnets, weak ferromagnets or even in metallic magnets. Our work is mainly focused on the point to explain the Curie-Weiss like behavior in aforementioned magnets because the necessary condition for this behaviour is not known yet. To calculate dynamical susceptibilities, additional free energy as a function of magnetization is expressed in terms of transversal dynamical susceptibilities which are calculated by employing the modified random phase approximation. Further the properties of spin fluctuations are also explored along with the approximate prediction of Tc. It is found that spin fluctuations are important in understanding the true cause of magnetism in such magnets. However, there are several reported difficulties with the SCR theory in calculating the exact value of spin fluctuations and Curie-Weiss susceptibilities. Most of them are settled now and we are planning to apply this theory to study thermodynamic properties of realistic magnets in comparison with experimental data.

Constraint on primordial magnetic fields in the light of ARCADE 2 and EDGES observations

Date: 2021-06-17
Speaker: Pravin Kumar Natwariya
Venue: Online --> https://bluejeans.com/335834835/9609

Abstract

We have studied the upper constraints on primordial magnetic fields (PMFs) in the light of the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) low-band observation and Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission (ARCADE 2). ARCADE 2 observation detected extra-galactic excess radio radiation in the frequency range 3-90 GHz. The enhancement in the radio radiation is also supported by the first station of the Long Wavelength Array (LWA1) in the frequency range of 40-80 MHz. The presence of early radiation excess over the cosmic microwave background can not be completely ruled out, and it may explain the EDGES anomaly. In the presence of decaying PMFs, 21 cm differential brightness temperature can modify due to the heating of the gas by decaying magnetic fields, and we can constraint the present-day strength of the primordial magnetic fields.

Flavor specific neutrino self-interaction: $H_0$ Tension and IceCube

Date: 2021-03-18
Speaker: Priyank Parashari
Venue: Online

Abstract

Over the past few decades, the huge influx of data from cosmological and particle physics observations have enabled us to understand and test the viability of the theories. However, these observations have also yielded some discrepancies which hint towards the new physics. One such discrepancy is the mismatch between the value of the Hubble constant ($H_0$) obtained from the direct local measurements and that inferred from the Planck CMB observation within $\Lambda$CDM cosmology. This is known as the $H_0$ tension. Self-interaction between active neutrinos had been proposed as a solution to the $H_0$ tension. Similar self-interaction can also explain the observed dips in the flux of the neutrinos in IceCube detectors. In this talk, I will explain the $H_0$ tension and observed dips in IceCUbe as a signature of flavor specific self-interaction between active neutrinos.

Yu-Shiba-Rusinov states of single magnetic molecule in an s−wave superconductor

Date: 2021-03-11
Speaker: Saurabh Pradhan
Venue: Online

Abstract

We use the numerical renormalization group theory to investigate the Yu-Shiba-Rusinov (YSR) bound state properties of single magnetic molecules placed in an s-wave superconducting substrate. The molecule consists of a large core spin and a single orbital, coupled via exchange interaction. The critical Coulomb interaction for the singlet/doublet transition decreases in the presence of this exchange interaction for both Ferro and anti-ferromagnetic couplings.The number of YSR states also increases to two pairs, however, in the singlet phase, one of the pairs has zero spectral weight. We explore the evolution of the in-gap states using the Anderson model. Away from the particle-hole symmetry point, the results suggest a doublet-singlet-doublet transition as the on-site energy is lowered while keeping the Coulomb interaction fixed. To understand these results, we write down an effective model for the molecule in the limit of a large superconducting order parameter. Qualitatively, it explains the various phase transitions and spectral nature of the in-gap states.

2019

Model-independent Astrophysical Constraints on Leptophilic Dark Matter in the Framework of Tsallis Statistics

Date: 2019-08-23
Speaker: Atanu Guha
Venue: Theoretical Physics Seminar Room / 469

Abstract

I will discuss model-independent astrophysical constraints on leptophilic dark matter (DM), considering its thermal production in a supernova core and taking into account core temperature fluctuations within the framework of q-deformed Tsallis statistics. In an effective field theory approach, where the DM fermions interact with the Standard Model via dimension-six operators of either scalar-pseudoscalar, vector-axial vector, or tensor-axial tensor type, we obtain bounds on the effective cut-off scale Λ from supernova cooling and free-streaming of DM from supernova core, and from thermal relic density considerations, depending on the DM mass and the q-deformation parameter.

2018

TBA

Date: 2018-09-04
Speaker: Rukmani
Venue: Room No. 469

Abstract

TBA

Some comments on Thapa-Pandey's discovery of room temperature superconductivity at IISc Bangalore

Date: 2018-08-30
Speaker: Dr. Navinder Singh, (THEPH, PRL)
Venue: Room No. 469

Abstract

Silver and gold are not good superconductors, they superconduct at micro Kelvin temperatures. At IISc Bangalore, Thapa and Pandey discovered that their amalgam consisting nanoparticles can superconduct at room temperature! If true and verified independently,this will be greatest discovery in the field of superconductivity. However, the discovery is veiled by an unexpected correlations in data. We present some comments on these developments.

Constraining TeV scale Seesaw Models from electroweak vacuum stability/metastability.

Date: 2018-08-20
Speaker: Mr. Vishnudath, Physical Research Laboratory
Venue: Room No. 469

Abstract

The discovery of the Higgs boson with a mass of 125 GeV was a mileston in particle physics and it indicates that the Standard Model (SM) electroweak vacuum is metastable. But this is under the assumption that SM is the true theory up to the Planck scale. One of the major issues that SM does not have an answer to is the non-zero masses of the neutrinos as indicated by various neutrino oscillation experiments. Among the various proposals for neutrino mass generation, seesaw mechanism is the most famous one. In this talk, I will discuss how the new physics parameters could be constrained from the stability/metastability arguments in the context of natural type-3 seesaw model. We also consider the constraints coming from charged lepton flavor violating decays. Finally, I will also discuss a class of gauged U(1) extensions with inverse seesaw mechanism.

Probing Inert Higgs model with Jet-substructure

Date: 2018-08-20
Speaker: Ms. Akanksha Bhardwaj (PRL)
Venue: Room No. 469

Abstract

The Inert Higgs doublet model (IDM) is a theoretically well-motivated model among the Minimal Consistent Dark Matter (MCDM) models and provides many interesting signatures at the LHC. For hierarchical IDM scalar spectrum, the usual searches at the LHC are not efficient enough. In this ongoing work, we propose a new signature (2 Fat-jet + MET) to search for this interesting parameter space of this model. We choose the benchmark points by performing the parameter scan which satisfies all the theoretical and experimental constraints. We perform our analysis for light DM scenarios with the mass of 50-70 GeV, where we probe both the charged and the CP-odd Higgs in 300-700 GeV mass range. We exploit the characteristics of the jet substructure techniques which can lead to the discovery of the 2 fatjet + MET signal with the integrated luminosity of 3000 $fb^{-1}$ at the 13 TeV LHC.

Approximate methods to model cosmological non-linear large scale structure

Date: 2018-08-20
Speaker: Dr. Sharvari Nadkarni-Ghosh (IIT Kanpur)
Venue: Room No. 469

Abstract

cosmological observations have shown that on large scales, matter is distributed into high density regions such as galaxies, clusters etc. and low density voids. Understanding how this large scale structure (LSS) arose from tiny quantum fluctuations set during inflation, is one of the important aims of cosmology today. The reason for this is because the evolution history depends sensitively upon the cosmological model and observations of LSS can help constrain the modelâ€™s parameters. Numerical simulations are widely employed to track the evolution into the non-linear regime; however they are slow. Given the wide range of cosmological models, this proves to be prohibitive and alternate analytic methods are necessary. Although approximate, they are not only faster but also provide valuable insight into the results of simulations. In this talk, I will describe two such approximate methods to model the non-linear evolution of large scale structure: Lagrangian perturbation theory (LPT) and ellipsoidal collapse. I will discuss the domain of validity of these methods and illustrate some applications.

Dark matter direct detection

Date: 2018-08-20
Speaker: Dr. Gaurav Tomar, Sogang Univ. Korea
Venue: Room No. 469

Abstract

Guided by non-relativistic EFT, we classify the most general interactions between scalar or fermionic WIMP and nuclei. Recently, we studied exclusion plots for different types of interactions which in WIMPs direct detection are the measure of the relative sensitivity of different experiments. We analyzed exclusion plots for newly arising non-standard interactions for existing experiments including the effects of isospin violation. We also discussed the spectral shape in WIMPs effective models and present the exclusion plots for current as well as future experiments. In this talk, we will talk about it in more details including the lastest result from DAMA phase-2 experiment.

Gutzwiller mean field theory and exact diagonalization method for Bose-Hubbard model.

Date: 2018-08-16
Speaker: Mr. Soumik Bandhopadhyay
Venue: Room No. 469

Abstract

Bose-Hubbard model stands as the prototypical model to capture the physics of ultracold bosons in optical lattices. During this talk, I will describe three different methodologies, that is, single-site Gutzwiller mean field (SGMF), cluster Gutzwiller mean field (CGMF), and exact diagonalization (ED), which we have used to solve the model Hamiltonian in our studies. In order to emphasize the merits and drawbacks of each method, we will discuss on distinct quantum phases and their characteristics, exhibited by neutral and dipolar bosons in perfect or disordered optical lattices.

Sterile Neutrino Search

Date: 2018-08-06
Speaker: Mr. Kaustav Chakraborty (PRL)
Venue: Room No. 469

Abstract

The recent MiniBooNE data is consistent in energy and magnitude with the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND). This excess corresponds to a ∆m2 ∼ 0.04eV which hints towards the presence of a light sterile neutrino. I will talk on the evidence of sterile neutrino and the future prospects of sterile neutrino search. I will also talk on ‘partial µ-τ ’ reflection symmetry in the context of sterile neutrino. The predictions of this symmetry is compared with the allowed area in the sin2θ23 − δCP plane as obtained from the global analysis of neutrino oscillation data.

A ROBUST SIGNATURE OF ELECTRON HYDRODYNAMICS IN 2D MATERIALS

Date: 2018-08-02
Speaker: Prof. Deshdeep Sahdev, Quazar Tech, (New Delhi)
Venue: Room No. 469

Abstract

Electron transport can transition from Ohmic to hydrodynamic when electron-electron scattering dominates, as shown in several recent experiments in systems such as Graphene. We show that microwave-frequency AC sources can excite hydrodynamic behavior involving vigorous vortex generation and reconnection, far more easily than the DC sources used so far. We identify the change of sign in a nonlocal current-voltage phase as a robust probe of the transition to the electronic hydrodynamic regime.

Inflationary Cosmology: Theory and Observations

Date: 2018-07-30
Speaker: Ms. Richa Arya (PRL)
Venue: Room No. 469

Abstract

Cosmological Inflation is a phase of accelerated expansion for a very brief duration in the early Universe. It provides a solution to many shortcomings of the Standard Big Bang Model of cosmology. As a bonus, it also generates the density fluctuations that explain the anisotropies in the Cosmic Microwave Background (CMB) radiation and seeds the growth of Large-Scale Structures (LSS) at the late time. In this talk, I will review the inflationary paradigm and discuss various inflationary models and their status from the current CMB observations. I will also discuss some results of our study on the Warm Inflationary models.

Non-holomorphic supersymmetry and scalar sequestering

Date: 2018-07-27
Speaker: Sabyasachi Chakraborty, TIFR Mumbai
Venue: Room No. 469

Abstract

Scalar sequestering ensure vanishing masses for supersymmetric scalars at high scales. This interesting feature is a result of strong dynamics in the hidden sector and highly motivated from the perspective of electroweak fine tuning. In such a scenario, gaugino mediated loop suppressed contributions generate scalar masses at the TeV scale. Naturally, right handed sleptons turn out to be the lightest SUSY particles rendering a cosmologically unfavorable spectrum. In this work, we solve this issue by considering non-holomorphic soft susy breaking operators. We found out that the presence of such operators leaves a non-trivial imprint on the renormalization group evolutions of the scalar masses, resulting in a viable spectrum. Extension of this result can also be applied to other frameworks such as no-scale SUGRA, gaugino mediation, anomaly mediation etc.

TBA

Date: 2018-07-26
Speaker: Mr. Ashish Narang (PRL)
Venue: Room No. 469

Abstract

TBA

Constraint on viscosity of dark matter from the 21 cm signal

Date: 2018-07-19
Speaker: Mr. Arvind Kumar Mishra (PRL)
Venue: Room No. 469

Abstract

Recently the Experiment to Detect the Global Epoch of Re-ionization Signature (EDGES) has reported an absorption signal of 21cm emitted from the hyperfine splitting of the neutral hydrogen in the cosmic dawn era. The amplitude of this absorption dip indicates that the baryons were much cooler than as expected from the standard cosmology. This can be explained by considering the interaction between dark matter and baryonic matter. In the standard cosmology, one assumes the dark matter to be an ideal fluid. In our work, we consider dark matter as a viscous fluid and try to constraint its viscosity from the 21 cm signal. In this talk, I will discuss about the 21 cm signal and show some preliminary results of our work.

Quarkonia: A probe of QGP

Date: 2018-07-12
Speaker: Mr. Balbeer Singh (PRL)
Venue: Room No. 469

Abstract

Quark-gluon plasma (QGP) is the deconfined state of strongly interacting matter. Experimentally, this phase is accessible by colliding two heavy nuclei at sufficiently high energy. In view of this, RHIC@Brookhaven and LHC@CERN have created a unique opportunity to study the properties of QGP. In addition, a very strong magnetic field is also created at the initial stages of the collision which however decreases very rapidly and has a significant effect on the medium. The global properties of this deconfined matter are characterized by measurement of particles in low and high transverse momentum regime, jets, elliptic flow etc. In this regard, suppression of Quarkonium is considered as one of the important probes for QGP. In this talk, I will talk about the effect of magnetic field on heavy quark complex potential. Furthermore, I will also talk about the matrix model of semi QGP.

$\sigma_8$ tension and neutrino mass in dark energy models

Date: 2018-07-09
Speaker: Mr. Priyank Parashari (Physical Research Laboratory, Ahmedabad)
Venue: Room No. 469

Abstract

The current observations indicate that the present Universe is undergoing the accelerated expansion, which can be explained by the presence of dark energy (DE). The cosmological constant is the simplest candidate for dark energy but it has some problems. In this talk, I will discuss two DE models, (1) Hu-Sawicki (HS) Model of f(R) gravity and (2) Chavallier-Polarski-Linder (CPL) parameterization of dynamical dark energy (DDE), both of which explain the cosmic expansion. Also, in the standard model of cosmology it has been pointed out that there exists a tension in $\sigma_8-\Omega_m$ measurement between CMB and LSS observation. We compute $\sigma_8$ consistent with the parameters of HS and DDE models.I will discuss the status of $\sigma_8$ tension in the HS and DDE models. Since modified cosmology models change the matter power spectrum which also depends upon the neutrino mass, bound on neutrino mass gets modified. I will also discuss the bound on neutrino mass in the HS and DDE models.

Pinning the light pseudoscalar in Lepton Specific 2HDM

Date: 2018-07-03
Speaker: Mr. Siddharth Dwivedi, (Harish-Chandra Research Institute, Allahabad)
Venue: Room No. 469

Abstract

We investigate the detectability as well as reconstructibility of a light pseudoscalar particle $A$, of mass in the 50 -- 60 GeV range, which is still allowed in a Type-X (lepton-specific) two-Higgs doublet scenario. Such a pseudoscalar can be pair-produced in the decay $ h\to AA$ of the 125 GeV scalar $ h $. The light pseudoscalar in the aforementioned range, helpful in explaining the muon anomalous magnetic moment, has not only substantial branching ratio in the $\tau^+ \tau^-$ channel but also one of about $0.35\%$ in the $\mu^+\mu^-$ final state. We show how to faithfully reconstruct the $A$ mass using the $\mu^+\mu^-$ mode, and establish the existence of a pseudoscalar around 50 -- 60 GeV, using the process $pp \to h \to AA \to \mu^+\mu^- , \tau^+ \tau^-$. This is one of the most reliable ways of reconstructing the light $A$ mass, with a statistical significance that amounts to discovery, within the luminosity reach of Run-II at LHC.

Photon probes at colliders

Date: 2018-06-29
Speaker: Ms. Disha Bhatia (TIFR Mumbai)
Venue: Room No. 469

Abstract

In this talk, I will be mainly concentrating on two new physics scenarios--- light and heavy, which could give rise to apparent diphoton signatures at LHC. I will be describing their phenomenological implications and detection methods in detail.

TBA

Date: 2018-06-28
Speaker: Mr. Bhavesh Chauhan
Venue: Room No. 469

Abstract

TBA

Topic- Color Superconductivity for Magnetized three flavour quark matter

Date: 2018-06-21
Speaker: Mr. Aman Abhishek
Venue: Room No. 469

Abstract

At high enough density the quark matter becomes deconfined and the fermi surface is unstable to cooper pair formation. Such a phenomenon is known as Color superconductivity. There are various phases of color superconductivity which can be modified in the presence of external background magnetic field. Such a phase may be present in the interior of neutron stars. In the present work we study the color superconductivity in three flavor quark matter in the presence of magnetic field within the framework of Nambu-Jona Lasinio model. I will also discuss the effect of charge neutrality on color superconductivity.

Decoding cosmic fingerprints: constraining the generation and evolution of primordial fluctuations

Date: 2018-06-14
Speaker: Dhiraj kumar hazra
Venue: Room No. 469

Abstract

It is the origin and evolution of quantum fluctuations that eventually lead to the formation of the Large Scale Structure (LSS) in the Universe. The primordial perturbations emerge through the radiation and thereafter the matter dominated epochs and finally to today's dark energy dominated epoch, leaving their distinct fingerprints in the photons that we observe. Photons from the Cosmic Microwave Background (CMB), quasars, galaxies and clusters, supernovae, stars etc. can be analyzed to trace these fingerprints. In this talk, I will mainly discuss decoding three different fingerprints originating from three different epochs in the timeline of the Universe, namely, CMB from the last scattering surface, Lyman-alpha observations from reionization and post-reionization eras and the galaxies observed in the LSS. Since signals from different cosmological processes are convolved in our observations, effective joint analyses are required to converge towards the most probable model of the Universe. I will outline the standard model and few extensions beyond that agree remarkably with the present data. I will also discuss model independent reconstruction methods that can lead to possible scenarios of the Universe directly from the data. I will conclude with forecasts from the upcoming and proposed cosmological missions.

TBA

Date: 2018-06-04
Speaker: Mr. Arun Kumar Pandey
Venue: Room No. 469

Abstract

TBA

Constraining black-hole spins with gravitational wave observations

Date: 2018-04-06
Speaker: Dr. Vaibhav Tiwari (Cardiff University, UK)
Venue: Room No. 469

Abstract

Observations of gravitational waves from merging black-hole binaries are beginning to teach us about the population of stellar-mass black holes in the universe. An individual observation allows measurements of the black-hole masses, but only limited information about the black-hole spins, both their magnitude and orientation. Previous work has shown that from multiple signals we can infer the distribution of spin orientations, which allows us to distinguish between formation and evolution scenarios. In my presentation, I will go over some basics of population analysis and will show how by taking into account the variation in the signal strength with spin magnitude, the mass distribution of black holes, and the signal degeneracy between mass-ratio and spin the scenarios can be greatly constrained.

Heavy quarks as probes of longitudinal structure of the fireball in relativistic heavy ion collisions

Date: 2018-04-03
Speaker: Dr. Sandeep Chatterjee ( AGH Univ. Of Science and Tech, Krakow)
Venue: Room No. 469

Abstract

While the transverse dynamics of relativistic heavy ion collisions has been studied in great details, understanding the longitudinal structure and the related breaking of boost invariance along the beam direction is still at an early stage. In this talk, we will discuss our recent proposal of the use of heavy quarks as excellent probe of this forward-backward symmetry breaking.

Recent developments in QCD thermodynamics from HTL effective theory

Date: 2018-03-22
Speaker: Dr. Najmul Haque
Venue: Room No. 469

Abstract

Hard-Thermal-Loop (HTL) perturbation theory is a gauge-invariant reorganization of usual perturbation theory at finite temperature and chemical potential where higher order diagrams contribute to the lower order one. In this talk, I will summarize recent developments in the HTL approach to QCD, specially the study of QCD Equation of State. First I will briefly discuss about the HTL perturbation theory and then I will present the finite-temperature and -density calculation of QCD thermodynamics at NNLO from the HTL perturbation theory. Then I will discuss generalization of the HTL framework including the magnetic scale (g^2T) resummation and also including finite quark masses and finally the results of the second order susceptibility at this two new frameworks.

Modeling and analysis of food data to leverage it for nutrition and health

Date: 2018-01-18
Speaker: Dr Ganesh Bagler (Center for Computational Biology, IIIT-Delhi)
Venue: Room No. 469

Abstract

Cooking is central to the identity of Homo sapiens. Starting with a seemingly simple question, ‘Why do we eat what we eat?’, data-driven research conducted from our lab have led to the serendipitous discovery of ‘contrasting food pairing’ in Indian cuisine. Our studies have also revealed ‘culinary fingerprints’ of regional cuisines and role of spice as the molecular fulcrum of Indian recipes. Apart from answering one question, our research has opened up many more questions that are leading us into divergent frontiers of food, nutrition, and health: models for the evolution of recipes, molecular basis of ingredient flavors, emergence of the flavor in a recipe, algorithms for novel recipe generation, fooddisease associations, the therapeutic potential of phytochemicals and strategies forleveraging food as medicine, among others. Through the construction of relevant data resources and hypothesis-driven investigations of food, our data-driven explorations of food have opened a whole new paradigm for food data analytics and show the potential for leveraging food for better health as well as nutrition.

Probing the self-couplings of the Higgs boson at the LHC: Current status and future prospects

Date: 2018-01-02
Speaker: Ambresh shivaji
Venue: Room No. 469

Abstract

In the standard model (SM) of particle physics, the Higgs potential depends on two parameters: \mu, the coefficient of the quadratic term and \lambda, the coefficient of the quartic interaction. As a result of the electroweak symmetry breaking, the Higgs potential gives rise to the mass and the self-couplings (trilinear and quartic couplings) of the Higgs boson. Knowing the scale of the electroweak symmetry breaking (v) and the Higgs boson mass (MH), fixes the self-couplings of the Higgs boson completely. However, in presence of new physics affecting the Higgs potential, the predictions for the Higgs self-couplings might change. Therefore, in the light of ongoing searches for new physics signals beyond the SM, it is important that we measure the self-couplings of the Higgs boson independently. In my talk, I will describe direct and indirect methods of probing Higgs self-couplings at the Large Hadron Collider (LHC). I will review the current and future sensitivities towards the measurements of Higgs self-couplings in multi-Higgs production channels, and emphasize the role of the observables and higher-order effects in achieving a better sensitivity at the LHC.

2017

Non-equilibrium spin dynamics of interacting quantum systems

Date: 2017-12-21
Speaker: Dr. Manan Vyas (Instituto de Ciencias Físicas, UNAM, MEX-62210 Cuernavaca, Morelos, Mexico)
Venue: Room No. 469

Abstract

We analyze relaxation dynamics of the survival probability and information entropy of a many-particle fermionic (bosonic) system in a mean-field, quenched by a random two-body interaction (preserving many-particle spin) as a function of spin degrees of freedom. The system Hamiltonian is represented by an embedded Gaussian orthogonal ensemble (EGOE) of random matrices (for time-reversal and rotationally invariant systems) with one plus two-body interactions for fermions (bosons). A simple general picture, in which the spectral variances play a central role, is achieved for describing the short-time spin dynamics of the survival probability and information entropy.

Emergent quantum heat pump in a driven quantum gas

Date: 2017-12-13
Speaker: Dr. Arko Roy (Max Planck Institute for the Physics of Complex Systems, Dresden, Germany)
Venue: Room No: 469

Abstract

We propose a novel scheme for quantum heat pumps powered by rapid time-periodic driving. We focus our investigation on a system consisting of two coupled driven quantum dots in contact with fermionic reservoirs at different temperatures. Such a configuration can be realized in a quantum-gas microscope. Theoretically we characterize the device by describing the coupling to the reservoirs using the Floquet-Born-Markov approximation.

Novel quantum phases of ultracold bosonic atoms in optical lattices

Date: 2017-12-05
Speaker: Dr. Kuldeep Suthar
Venue: Room no:469

Abstract

Ultracold atoms provide a novel route to exotic quantum phases of matter. In particular, phases which display coexistence of different types of order. For example, can a solid be superfluid? The quest for this state has been one of the grand challenges in condensed matter physics and dates back to the first prediction of supersolid in $^{4}$He. Supersolidity combines superfluid properties with long-range spatial periodicity of solids. Recent experiments have reported the observation of characteristic signatures of this phase in ultracold quantum matter. To study various quantum phases and their transitions we employ Gutzwiller mean-field approximation in extended Bose-Hubbard model. In this talk, we shall discuss the phase diagram, the effect of synthetic magnetic field on phases and stability of supersolid phase in the presence of long-range interactions.

Disparity of Larmor's formula with energy-momentum conservation

Date: 2017-11-30
Speaker: Dr. Ashok Kumar Singal (PRL)
Venue: Room No. 469

Abstract

The well-known Larmor's formula, which yields power losses of a radiating charge proportional to the square of its acceleration, is not compatible with energy-momentum conservation. In fact, the radiative loss picture derived from Larmor's formula is not consistent with the special theory of relativity. One needs to clearly distinguish between the rate of energy-momentum being carried away by the electromagnetic radiation and that of mechanical energy-momentum losses being incurred by the radiating charge. In literature both power rates are treated as not only equal but almost synonymous. This 100-year old oversight is due to a mathematical subtlety that has been missed in the applicability of Poynting's theorem.

A hybrid setup for fundamental unknowns using T2HK and $\mu$-DAR

Date: 2017-11-28
Speaker: Dr. Monojit Ghosh (Tokyo Metropolitan University)
Venue: Room No. 469

Abstract

Neutrino mass hierarchy, CP-violation, and octant of $\theta_{23}$ are the fundamental unknowns in neutrino oscillations. In order to address all these three unknowns, we study the physics reach of a setup, where we replace the antineutrino run of T2HK with antineutrinos from muon decay at rest ($\mu$-DAR).

Lepton Non-Universality and recent excitements in Flavour physics

Date: 2017-11-23
Speaker: Dr. Debjyoti Bardhan (TIFR, Mumbai)
Venue: Room no:469

Abstract

While the Standard Model (SM) has so far proved to be extremely robust and no concrete evidence of New Physics has been found, certain recent measurements relating to B-meson decays have shown tantalising hints of deviation from the SM expectations. In this context, many claims of NP have been made. I will discuss both the neutral and charged current decays of the B-meson, highlighting the different deviations observed, and then describe a model-independent approach to New Physics, based on our papers.

EXPERIMENTAL HIGH ENERGY ASTROPHYSICS

Date: 2017-11-14
Speaker: Dr. P. R. Vishwanath
Venue: Room No. 469

Abstract

I give a historical perspective of the experiments in gamma ray detection conducted in India.

PLANCK vs LSS : Tension and solutions

Date: 2017-10-18
Speaker: Dr. Arindam Mazumdar (Physical research laboratory, Ahmedabad)
Venue: Room No. 469

Abstract

Primordial perturbations generated at the time of Inflation is expected to produce the fluctuations in CMB as well as the large scale structures(LSS) of the universe.Standard LambdaCDM theory is expected to describe these CMB observations and LSS observations under a single theoretical framework. However,some recent observations have pointed out some tensions between these two types of observations under LambdaCDM theory. In this talk I will cover some earlier attempts to resolve these tensions.Then I will describe our attempt with viscous cold dark matter to resolve the problem.

Correlation effects in strong field enhanced ionization of molecules : A time-dependent generalized-active-space configuration-interaction study.

Date: 2017-10-12
Speaker: Dr. Siddhartha Chattopadhyay (Max Planck Institute for Nuclear Physics, Heidelberg, Germany)
Venue: Room No. 469

Abstract

In this talk, I will present recent results on the correlation effects in strong field ionization of diatomic molecules. In this work, we have studied $\mathrm{H}_2$, $\mathrm{LiH}$, and $\mathrm{HF}$ molecules, aligned collinearly with the linear polarization of the external field.To elucidate the possible role of electron correlation in the enhanced-ionization (EI) phenomena we consider different levels of approximation with the time-dependent generalized-active-space configuration-interaction (TD-GASCI) method. The results of our studies show that correlation is important and they also demonstrate significant deviations between the results of the single-active-electron approximation and more accurate configuration-interaction methods.We will further investigate the role of low-lying excited states in the EI phenomena. With the inclusion of correlation we show strong carrier-envelope-phase effects in the EI of the asymmetric heteronuclear $\mathrm{LiH}$ molecule. The correlated calculation shows an intriguing feature of cross-over in enhanced ionization with two carrier-envelope-phases at criticalinter-nuclear separation.

Control in open quantum systems out of equilibrium

Date: 2017-10-09
Speaker: Dr. Victor Mukherjee ( Weizmann Institute of Science, Rehovot, Israel)
Venue: Room No:469

Abstract

Control in open quantum systems out of equilibrium is necessary to achieve various tasks, ranging from efficient cooling or heating of the systems, controlling decoherence in open quantum systems, to engineering quantum technologies, such as quantum heat engines and quantum probes. I will talk about control in quantum systems out of equilibrium in presence of Markovian and non-Markovian baths, as well as use of control in quantum technologies.

Novel phenomenological features of neutrinophilic two Higgs doublet model

Date: 2017-09-28
Speaker: Dr. Soumya Sadhukhan (Physical research laboratory, Ahmedabad)
Venue: Room No. 469

Abstract

Decay of active neutrinos is one of the possibilities that can explain the depletion of the neutrino flux detected in the IceCube experiment at an energy around the PeV scale.Here we explore the decay of neutrinos and subsequent decrease in neutrino count in the framework of a neutrinophilic two Higgs doublet model (2HDM). It is also discussed how the non standard interaction (NSI) of neutrinos can arise in a modified neutrinophilic 2HDM scenario. There are also comments on various theoretical and experimental constraints that can affect the explanation of these phenomenological features.

Setting Initial Conditions for Inflation with Reaction-Diffusion Equation

Date: 2017-09-21
Speaker: Mr. Arpan Das (Institute of Physics, Bhubaneswar)
Venue: Room No. 469

Abstract

We discuss the issue of setting appropriate initial conditions for inflation. Specifically, we consider natural inflation model and discuss the fine tuning required for setting almost homogeneous initial conditions over a region of order several times the Hubble size which is orders of magnitude larger than any relevant correlation length for field fluctuations. We then propose to use the special propagating front solutions of reaction-diffusion equations for localized field domains of much smaller sizes. Due to very small velocities of these propagating fronts we find that the inflaton field in such a small field domain changes very slowly, contrary to naive expectation of rapid roll down to the true vacuum. Continued expansion leads to the energy density in the Hubble region being dominated by the vacuum energy, thereby beginning the inflationary phase. Our results show that inflation can occur even with a single localized field domain of size much smaller than the Hubble size. We discuss possible extensions of our results for different inflationary models, as well as various limitations of our analysis (e.g. neglecting self gravity of the localized field domain).

Gravity, Thermodynamics and Null Surfaces

Date: 2017-09-07
Speaker: Dr. Sumanta Chakraborty
Venue: Room No: 469

Abstract

In the first part of my talk I will discuss the variational principle for general relativity and some associated subtle facts not shared by other interactions present in nature. In particular null surfaces play a very interesting role throughout the development of general relativity on which I will elaborate upon. A brief idea of black hole thermodynamics and Hawking effect will also be provided. In the second part of my talk, I will discuss the thermodynamics of null surfaces. In particular, I will show that three different projections of gravitational momentum related to an arbitrary null surface in the spacetime lead to three different equations, all of which have thermodynamic interpretations. The implications will be discussed.

TBA

Date: 2017-08-31
Speaker: Dr. Uma Shankar Gupta (University of Allahabad)
Venue: Room No. 469

Abstract

TBA

A glimpse of quantum Hall physics for optically trapped Bosons

Date: 2017-08-24
Speaker: Dr. Sukla Pal
Venue: Room No:469

Abstract

Emergence of quantum Hall states in cold atoms recently has captured much attention. In this seminar, I will present few basic aspects to implement quantum Hall states for Bosons trapped in optical lattice. Considering Bose Hubbard model (BHM), I will describe the behavior of interacting Bosons in an optical lattice subjected to a synthetic magnetic field where the system can have a possibility to enter into the quantum Hall regime. In presence of random local impurities, the equilibrium phase diagram differs from clean one – - a new gapless phase-Bose glass phase appears as an equilibrium solution of disordered BHM.

A novel spontaneous $CP$ nonconservation

Date: 2017-08-17
Speaker: Dr. Gauhar Abbas (PRL

Abstract

A new type of spontaneous $CP$ breaking in a class of models will be discussed. Consequences of spontaneous $CP$ breaking (in this class of models) are non-trivial for fine-tuning of the standard model Higgs mass, the strong CP problem, neutrino masses, dark matter and baryogenesis. An explanation for recently observed anomalies in the transitions b-> sll and b-> c l \nu is obtained naturally.

Impurity textures in a Chern insulator

Date: 2017-08-10
Speaker: Mr. Vibhuti Bhusan Jha (SAC)
Venue: Room No. 469

Abstract

Chern insulators arguably provide the simplest examples of topological phases. They are characterized by a topological invariant and can be identified by the presence of protected edge states. A local impurity in a Chern insulator induces a twofold response: bound states that carry a chiral current and a net current circulating around the impurity. This is a manifestation of broken time reversal symmetry and persists even for an infinitesimal impurity potential. To illustrate this, we consider a Coulomb impurity in the Haldane model. We show that an infinitesimal impurity strength suffices to create bound states. We find analytic wave functions for the bound states and show that they carry a circulating current. Both the cases of trivial and non trivial topology has been considered. In the many-body problem of the Haldane model at half-filling, we use a linear response approach to demonstrate a circulating current around the impurity. Impurity textures in insulators are generally expected to decay exponentially; in contrast, this current decays polynomially with distance from the impurity. Going beyond the Haldane model, we consider the case of coexisting trivial and nontrivial masses. We find that the impurity induces a local chiral current as long as time-reversal symmetry is broken. However, the decay of this local current bears a signature of the overall topology—the current decays polynomially in a nontrivial system and exponentially in a trivial system.

Searching for top squark in the compressed region of SUSY spectrum at the Large Hadron Collider

Date: 2017-08-08
Speaker: Dr. Abhaya Kumar Swain (PRL)
Venue: Room No. 469

Abstract

Searching for the top squark is very important in the context of stabilizing the Higgs boson mass against large quantum correction and gauge coupling unification. While Large Hadron Collider has already excluded large parameter space in supersymmetry, it poorly constrains the light top squark if the mass difference between the top squark and the neutralino is very small. Existing search strategy breaks down here mainly due to two reasons first, huge SM background and the second is unique compressed kinematics which makes all the decay products extremely soft. Here we propose a class of novel kinematic variables designed uniquely for the compressed region to control the huge SM background giving complimentary scheme in leptonic searches. We have considered the top squark undergoing four body decay in the leptonic channel and using this topology information our new kinematic variables significantly improve the current LHC limit.

Leptogenesis in R violating MSSM with one $L$ violating coupling and Majorana phase

Date: 2017-08-03
Speaker: Dr. Rathin Adhikari (CTP, University of Delhi)
Venue: Room No. 469

Abstract

We have shown a new scenario of successful leptogenesis with one L violating coupling and a relative Majorana phase playing the role of CP violation. This is in contrast to the usual consideration of diagrams with at least two L violating couplings. We have considered R-parity violating Minimal Supersymmetric Standard Model (MSSM) for leptogenesis at the TeV scale. This scenario is also consistent with generating appropriate light neutrino masses with the same L violating coupling.

Impact of the range of the interaction on the quantum dynamics of a bosonic Josephson junction.

Date: 2017-08-01
Speaker: Dr. Sudip Kumar Haldar (Kolkata West Bengal)
Venue: Room No. 469

Abstract

The out-of-equilibrium quantum dynamics of a bosonic Josephson junction (BJJ) with long-range interaction is studied in real space by solving the time-dependent many-body Schrödinger equation numerically accurately using the multiconfigurational time-dependent Hartree for bosons method. Having the many-boson wave-function at hand we can examine the impact of the range of the interaction on well-known features of the BJJ dynamics at both the mean-field and many-body level. We concentrate on the tunnelling frequency, survival probability, depletion and fragmentation, and position variance of the junction, and find competitive effect between the interaction and the confining trap. The presence of the tail part of the interaction basically enhances the effective repulsion as the range of the interaction is increased starting from a small value. But as the range becomes comparable with the trap size, the system approaches a situation where all the atoms feel a constant field and the impact of the tail on the dynamics diminishes. There is an optimal range of the interaction in which physical quantities in the junction are attaining their extreme values.

"Nuclear structure for dark matter detection"

Date: 2017-07-27
Speaker: Dr. R. Sahu (NIST Berhampur)
Venue: Room No. 469

Abstract

There are overwhelming evidences for the existence of dark matter in the universe. However,it has not yet been observed in earth-bound experiments nor created at particle colliders.Up to now, the nature of this matter remains a mystery. The event detection rates for the WIMP (a dark matter candidate) are calculated with 73Ge as the detector. The calculations are performed within the deformed shell model (DSM) based on Hartree-Fock states. First the energy levels and magnetic moment for the ground state and two low lying positive parity states for this nucleus are calculated and compared with experiment. The agreement is quite satisfactory. Then the nuclear wave functions are used to investigate the elastic and inelastic scattering of WIMP from 73Ge. The nuclear structure factors which are independent of supersymmetric model are also calculated as a function of WIMP mass. The event rates are calculated for a given set of SUSY parameters. The calculation shows that 73Ge is a good detector for detecting dark matter.

Dissecting Multi Photon Resonances at the Large Hadron Collider

Date: 2017-07-25
Speaker: Dr. Abhishek Iyer (TIFR Mumbai)
Venue: Room No. 469

Abstract

We examine the phenomenology of the production, at the 13 TeV Large Hadron Collider (LHC), of the production of a heavy resonance $X$, which decays via other new on-shell particles $n$ into multi- (i.e.\ three or more) photon final states.In the limit that $n$ is light compared to $X$, the multi-photon final state may dominantly appear as a two photon final state because the $\gamma$s from the $n$ decay are highly collinear and are not resolved. We discuss how to discriminate this scenario from $X \rightarrow \gamma \gamma$: rather than discarding nonisolated photons, it is better to relax the isolation criterion and instead form photon jet substructure variables. The spins of $X$ and $n$ leave their imprint upon the distribution of pseudorapidity gap $\Delta \eta$ between the apparent two photon states. Depending on the total integrated luminosity, this can be used in many cases to claim discrimination, although the case where $X$ and $n$ are both scalar particles cannot be discriminated from the direct $X \rightarrow \gamma \gamma$ decay in this manner. In addition, one can bound the mass of $n$ by the mass of each photon jet.

Viscous dark matter growth in (neo-) Newtonian cosmology

Date: 2017-07-20
Speaker: Mr. Arvind Kumar Mishra (PRL)
Venue: Room No. 469

Abstract

The cosmic structure formation on the subhorizon scale can be studied within the Newtonian framework of pressureless cold dark matter (CDM). However, if there is small but nonzero pressure of CDM then the Newtonian description will not be valid. In this talk we will argue that a new Newtonian approach will resolve the problem of Newtonian approach by incorporating pressure effects into the cosmic fluid dynamics and reproduces the general relativistic dynamics as well. Assuming that the CDM have small bulk viscosity, we will discuss about the effects of viscosity on the growth of scalar perturbations and put upper limit on the viscous coefficient.

Rare B decays as a probe of New Physics

Date: 2017-07-17
Speaker: Ms. Bharti Kindra (PRL)
Venue: Room No. 469

Abstract

Rare B decays have been used as testing grounds for the Standard Model.LHCb and Belle have measured optimized observables for B decaying to (K,K*)ll and reported several anomalies. Theoretical predictions for these observables are made using non-perturbative QCD calculations which are often plagued with large uncertainties.One can associate the observed anomalies either to these uncertainties, or some New Physics. In this talk we give predictions for these observables for other rare B decay modes which can be used to confirm the presence of New Physics.

SIMP: An alternate dark matter candidate

Date: 2017-07-13
Speaker: Mr. Ashish Narang (PRL)
Venue: Room No. 469

Abstract

A Weakly Interacting Massive Particle (WIMP) has been the preferred Dark Matter (DM) candidate. But the tightening of the constraints on the standard thermal WIMP scenario has forced physicists to propose alternative scenarios of DM. One such alternate scenario is the strongly interacting massive particle (SIMP) mechanism of dark matter freeze out. In this talk I will discuss one such DM model in which, under the assumption that DM annihilation into SM particles is suppressed, the SIMP mechanism dominates the freeze out of DM. I will show that a DM of MeV order mass with sufficiently strong self interaction gives the correct relic density of dark matter.

Effect of Long Range Force on Neutrino Oscillations

Date: 2017-07-11
Speaker: Mr. Kaustav Chakraborty (PRL)
Venue: Room No. 469

Abstract

Neutrino oscillation physics has been well studied under the framework of interactions governed by the Standard Model gauge group. But this gauge group can be extended to include an extra anomaly free U(1) symmetry Le − Lµ , Le − Lτ or Lµ − Lτ . Hence, the new gauge group becomes SU(3)C ⊗SU(2)L ⊗U(1)Y ⊗U(1)X. Under this new gauge group an extra Z’ boson is introduced, which, if sufficiently light will provide a Long Range Force which can significantly contribute to Neutrino Oscillations. I will discuss the theoretical and phenomenological aspects of Neutrino Oscillations under the effect of this Long Range Force.

Flavour structure from SO(10) X U(1) gauge theory in 6D

Date: 2017-07-07
Speaker: Dr. Ketan Patel (IISER Mohali)
Venue: Room No. 469

Abstract

I will briefly discuss an origin of quark-lepton multiplicities from the flux of an anomalous U(1) with SO(10) gauge theory in six dimensions. I will then describe how a realistic flavor phenomenology can be obtained in the framework.

Effect of non-standard neutrino interactions on the sensitivities of DUNE

Date: 2017-07-06
Speaker: Dr. K Naga Deepthi (PRL)
Venue: Room No. 469

Abstract

Deep Underground Neutrino Experiment (DUNE) is a potential long-baseline neutrino oscillation experiment of the next generation. It can act as a promising probe to new physics scenarios like non-standard neutrino interactions (NSI), which is a subleading phenomenon to the well established neutrino oscillations.In this work, we consider the effect of non-standard interactions (NSIs) on the propagation of neutrinos through matter and how they in turn affect the sensitivity of the DUNE in determining the mass hierarchy. We emphasize on the special case - when the diagonal NSI parameter ee = −1 at which the standard matter effect gets nullified. We show that, if in addition, there is maximal CP violation then this gives rise to an exact intrinsic hierarchy degeneracy, in the appearance channel, irrespective of the baseline and energy. Considering current model independent bounds on NSI parameters we observe that the hierarchy sensitivity of DUNE gets seriously compromised if NSI exists in nature. A signal of neutrino mass hierarchy at DUNE will therefore be able to rule out certain ranges of the NSI parameters. Additionally, we discuss the implications of ee = −1 (in the Earth) on MSW effect in the Sun.

A Song Of Ice And Flavor

Date: 2017-07-03
Speaker: Mr. Bhavesh Chauhan (PRL)
Venue: Room No. 469

Abstract

In the recent measurement of lepton flavor universality violation by LHCb, a 2.5 sigma deviation from the standard model prediction was observed. One of the most common explanations of these anomalies invokes leptoquarks with intergeneration Yukawa-like couplings. In this talk, I will show that the scalar doublet leptoquark with hypercharge 7/6 can accommodate these recent flavor anomalies along with the excess in the anomalous magnetic moment of the muon, and the very high energy neutrino events observed at IceCube. Within this framework, the flavor anomalies are generated at one loop level, and IceCube events are explained via resonant production of the leptoquark.

τ reconstruction to determine CP properties of the Higgs boson at the LHC

Date: 2017-06-27
Speaker: Ms. Akanksha Bhardwaj (PRL)
Venue: Room No. 469

Abstract

In our ongoing endeavor to uncover properties of the Higgs boson at the LHC, looking for event where the Higgs boson decays into third generation τ ’s is the natural first step in exploring the interactions of the Higgs boson with leptons. We propose a technique to reconstruct the full kinematics at the LHC to pin down the CP properties in the corresponding Yukawa coupling. The reconstruction technique works well for 1- prong decays as well as 3- prong decays. Hence several CP sensitive observable corresponding to different τ decay modes can be studied.

Z_N symmetry and Confinement-Deconfinement transition in SU(N)+Higgs theory

Date: 2017-06-22
Speaker: Dr. Minati Biswal (Institute of Mathematical Sciences, Chennai)
Venue: Room No. 469

Abstract

At very high temperatures, around ~150MeV, hadrons melt to form the QuarkGluon Plasma (QGP). Such extreme thermal conditions existed in the early Universe and currently are being created in heavy-ion collision experiments. Theoretical studies using Quantum ChromoDynamics (QCD) show that the melting of hadrons to QGP proceeds via the confinement-deconfinement (CD) transition. Interestingly this transition occurs in all SU(N) gauge theories like QCD. The nature of this transition depends greatly on the presence of matter fields. This has to do with the Z_N symmetry which describes well the CD transition when the matter fields are not considered. It is spontaneously broken in the deconfinement phase and gets restored in the confinement phase. The presence of matter fields is supposed to break this symmetry explicitly making the CD transition weaker. We study this explicit symmetry breaking in SU(N) gauge theories by considering only the bosonic matter fields. Contrary to conventional expectations we find vanishing explicit symmetry breaking in parts of the relevant phase diagrams.

Heavy quarkonia in a strong magnetic field

Date: 2017-06-20
Speaker: Mr. Balbeer Singh (PRL)
Venue: Room No. 469

Abstract

Quark-gluon plasma is the state of strongly interacting matter where quarks and gluons are deconfined and which is created in RHIC @ BNL and LHC @ CERN. In heavy ion collisions, a very strong magnetic field is also created in the noncentral collision of ions which is strong in the initial state of the collision and rapidly decreases with time. The presence of this magnetic field affects the QCD plasma screening which leads to observable changes in QGP properties. One of these is the heavy quarkonia potential and dissociation of quarkonia. In this seminar, I will discuss how the quarkonium potential gets modified in a magnetized quark-gluon plasma. I will also discuss the Debye screening in the lowest Landau level approximation and the quarkonium decay width in the strong field limit.

Collective modes of a hot anisotropic QCD medium with Bhatnagar-Gross-Krook collision term

Date: 2017-06-13
Speaker: Dr. Avdhesh Kumar (PRL)
Venue: Room No. 469

Abstract

In the heavy ion collision experiments the initial geometry of the hot QCD matter created is approximately almond shaped with only spatial anisotropy. Due to the expansion, the different pressure gradients in different directions cause a momentum anisotropy to develop which is present throughout the hydrodynamical expansion of the hot QCD matter. Therefore, it is inevitable to include such anisotropic effects while modeling a hot QCD medium. Collisions among the hard particles are responsible for the dissipation and needed for the hot QCD matter to reach the stage of equilibrium. Therefore, one simply can not ignore the collisions. Collective modes/excitation of hot QCD plasma can be understood as the collective motion that the plasma possesses due to the fluctuations in the equilibrium stage. The modes carry crucial information about the equilibrated QGP and play an important part in its dynamical evolution. The spectrum of the collective modes of the QGP can be studied with the help of the self-energy of the medium. In the seminar I shall discuss how the gluon self-energy of a hot anisotropic QCD medium (when medium interactions are also present) can be obtained using the semi-classical transport equation with Bhatnagar-Gross-Krook (BGK) collision term. I shall also discuss how the tensor decomposition of the gluon self energy leads to the structure functions which eventually control the dispersion relations and the collective mode structure of the medium.

Black Hole Horizon as a Fluid and the Outlines of a Transport Theory

Date: 2017-06-12
Speaker: Dr. Swastik Bhattacharya (IISER Thiruvananthapuram)
Venue: Room No. 469

Abstract

It has been known for a long time that the horizon of a black hole behaves like a viscous fluid. This is very suggestive in view of the fact that black holes possess a large entropy. Here we show how to construct a transport theory for the horizon-fluid with the final aim of developing a microscopic theory for this fluid. We shall determine the coefficient of bulk viscosity for the horizon-fluid and show that it indicates that the fluid system has a mass gap. Then we shall also briefly discuss the shear viscosity and the electrical conductivity of this fluid. Finally, based on the evidence gathered so far, I shall suggest what kind of field theory might be expected to underly the macroscopic picture of the horizon-fluid.

Spectral and transport responses of quark and hadronic matter

Date: 2017-06-08
Speaker: Dr. Sabyasachi Ghosh (University Of Calcuttta)
Venue: Room No. 469

Abstract

It is believed that up to a few microseconds after the Big Bang, the universe was in a state of quark matter followed by hadronic matter, with temperatures much larger than the temperature of the Sun. The experiments of heavy ion collisions like RHIC at BNL, USA and LHC at CERN, Switzerland have successfully produced this kind of an artificial baby universe, having a temperature of the order of a trillion degrees Kelvin, which is considered as the highest man-made temperature till now. Our studies focus on this early universe state by investigating its in-medium spectral and transport responses, where quantum field theory at finite temperature is used as the main mathematical tool. The investigation on spectral responses is aimed at explaining the so called “low mass dilepton enhancement”, as a signature of the medium, whereas the studies of transport responses have tried to probe the (nearly) perfect fluid nature of such a medium.

Review of Cosmological Perturbation Theory

Date: 2017-06-01
Speaker: Ms. Richa Arya (PRL)
Venue: Room No. 469

Abstract

Observations of the Cosmic Microwave Background (CMB) radiation indicate anisotropies in the temperature to be 1 part in 105 in a nearly uniform thermal radiation of 2.725 K. The presence of these anisotropies can be attributed to the primordial energy density fluctuations generated in the early Universe. In this talk I will discuss the mathematical tools and construction of Cosmological Perturbation Theory used to study these anisotropies. I will also discuss how the seed fluctuations generated in the early Universe evolve into the features in the angular power spectrum observed in the CMB today.

Effects of the trace anomaly on the Stochastic Gravitational Wave background

Date: 2017-05-25
Speaker: Mr. Sampurnanand
Venue: Room No. 469

Abstract

One of the important sources of the stochastic Gravitational Wave Background (SGW) is cosmological phase transitions. Apart from the dynamics of the phase transition, the characteristic frequency and the fractional energy density of the SGW depends upon the temperature of the transition. We compute the SGW spectrum in the light of QCD the equation of state provided by lattice results. We find that the inclusion of trace the anomaly enhances the SGW signal generated during the QCD phase transition by ~50% and the peak frequency of the QCD era SGW are shifted higher by ~25% as compared to the earlier estimates without trace anomaly. This result is extremely significant for testing the phase transition dynamics near the QCD epoch.

Common Origin of Neutrino Mass, Dark Matter and Dirac Leptogenesis

Date: 2017-05-11
Speaker: Dr. Arnab Dasgupta
Venue: Room No. 469

Abstract

We study the possibility of generating tiny Dirac neutrino masses at one loop level through the scotogenic mechanism such that one of the particles going inside the loop can be a stable cold dark matter (DM) candidate. Majorana mass terms of singlet fermions as well as tree level Dirac neutrino masses are prevented by incorporating the presence of additional discrete symmetries in a minimal fashion, which also guarantee the stability of the dark matter candidate. Due to the absence of total lepton number violation, the observed baryon asymmetry of the Universe is generated through the mechanism of Dirac leptogenesis (neutrinogenesis).

Quantum transport in the confined region of potential well and disordered wire

Date: 2017-04-28
Speaker: Dr. Surender Pratap
Venue: Room No. 469

Abstract

We report and adduced band structure in the confined region of potential well. LDOS, transmission, charge distribution have been calculated in the confined region of well. Transmission curves show oscillations with the increase of layers of unit cell. While in other part, we study level spacing distributions of finite sized 1-dimensional disordered systems. As the systems evolves from quasi ballistic to strongly localized regime, systems crosses over from strongly non-Wigner-Dyson type level spacing distribution to a universal Poisson distribution in the thermodynamic limit.

Generalizing Einstein's derivation of Planck's black-body radiation formula to non-equilibrium systems: the new concept of electro-magneto resistance.

Date: 2017-04-27
Speaker: Dr. Navinder Singh
Venue: Room No. 469

Abstract

In this first work under PRL's TDP project (No. TDP-ESR-623) we generalize the magneto-resistance phenomenon where the resistivity of materials change under a transverse magnetic field to a regime where in addition to magnetic field there is also a transverse ac field of resonant frequency with the Zeeman splitting. Our theoretical calculations predict this effect and the experiment to test it is under development (under TDP project). The idea is the following. In a magnetic field, electron spin levels are Zeeman split. If a resonant ac field is applied there is a new channel of momentum relaxation. An additional resistivity is predicted. The whole work is based upon a generalization of the Einstein's derivation of Planck's black-body radiation formula to non-equilibrium systems. This talk will summarize the theory work.

The Noncommutative Standard Model and its phenomenology

Date: 2017-04-21
Speaker: Mr. Selvaganapathy J
Venue: Room No. 469

Abstract

The existence of the principles of Quantum Mechanics and of Classical General Relativity points some difficulties at the small scale: the space-time uncertainty emerges from the Heisenberg principle, thereby suggesting that space-time has a quantum structure at small length scale: the space-time becomes fuzzy i.e. noncommutative(NC) at this scale. One of the property of the NC theory is that it is nonlocality inherent, which includes the gravity with standard model naturally. There is no theoretical prediction for energy scale at which noncommutative effects arise. So the energy scale can ranges from TeV scale to Planck scale. In this talk I would like to give a brief description about the non-commutative standard model (NCSM) and a phenomenological survey of this model. In particularly, I would like to discuss about neutral triple gauge boson interaction at LHC.At the end, I would like to discuss about the Drell-Yan process in the NCSM.

New Physics searches in radiative charm decays

Date: 2017-04-20
Speaker: Dr. Aritra Biswas
Venue: Room No. 469

Abstract

We show that for a heavy vector-like quark model with a down type isosinglet, branching ratio for c--> u gamma decay is enhanced by more than O(10^2) as compared to that in the Standard model when QCD corrections to next-to-leading order are incorporated. In a left-right symmetric model (LRSM) along with a heavy vector-like fermion, enhancement of this order can be achieved at the bare (QCD uncorrected) level itself. We propose that a measurement of the photon polarization could be used to signal the presence of such new physics inspite of the large long distance effects. We find that there is a large region within the allowed parameter space of the LRSM, as well as in the model with vector-like quark with additional left-right symmetry, where the photon polarization can be dominantly right-handed.

Texture Zero studies for the minimal extended type-I seesaw mechanism

Date: 2017-04-04
Speaker: Newton Nath
Venue: Room No. 469

Abstract

In this talk, we will discuss about the minimal extended type-I seesaw (MES) model which can give rise to eV scale sterile neutrino. In this model, three right handed neutrinos and one extra singlet S are added to generate a light sterile neutrino. We study the zero textures of the Yukawa matrices for the MES model. Remarkably we obtain only two allowed one-zero textures namely, m_{e\tau} = 0 and m_{\tau\tau}=0 having inverted hierarchical mass spectrum. We also discuss the importance of next-to-leading order correction terms in this model.

On Wave Breaking / Phase mixing of Relativistically Intense Longitudinal Waves in a Plasma

Date: 2017-03-30
Speaker: Prof. Sudip Sengupta
Venue: Room No. 469

Abstract

The study of the spatio-temporal evolution of a large amplitude longitudinal plasma oscillation or wave is a topic of fundamental importance in non-linear plasma physics. The amplitude of these nonlinear plasma waves is limited by a phenomenon called wave breaking, which may be induced by several physical processes. In this talk, along with a brief overview, current understanding of wave breaking of relativistically intense waves in a cold plasma will be presented. Extension to the warm plasma case in the non-relativistic limit will also be discussed.

Fermionic dark matter and supernova SN1987A cooling

Date: 2017-03-21
Speaker: Dr. Prasanta K Das
Venue: Room No. 469

Abstract

Light dark matter(1 − 30 MeV) particles which can be pair produced in electron-positron annihilation e − e + −→ χ χ inside the supernova SN1987A core take away the energy released in the supernova SN1987A explosion. Using the Raffelt’s criteria on the energy loss rate and using the optical depth criteria on the free streaming of the dark matter fermion, we find that the lower bound on the scale Λ of the dark matter effective theory to be Λ ∼ 10 8 TeV for m χ = 30 MeV. We extend our study in q-deformed statistics scenario and study the impact of it on the scale Λ .

Two new avenues in dark matter indirect detection

Date: 2017-03-21
Speaker: Dr. Ranjan Laha
Venue: Room No. 469

Abstract

Indirect detection is one of the major ways to search for dark matter. However, backgrounds have been a major problem for these searches. In this talk, I will introduce two new techniques to distinguish signal from background. Firstly, I will show how telescopes with ~ 0.1% energy resolution can exploit the Doppler shift of sharp photon features arising from dark matter interactions and separate the signal from background. The technique is general and I will give an example of this search strategy with the 3.5 keV line. In the second half of my talk, I will show how limits from the searches for very high energy photons can be used to constrain dark matter interactions. Using this observable, I will constrain very heavy dark matter which is very difficult to constrain using other means.

Pan-Starrs followup of Planck SZ clusters & Galactic Shapiro delay of Gravitational Waves

Date: 2017-03-20
Speaker: Dr. Shantanu Desai
Venue: Room No. 469

Abstract

The first half of the talk shall present results of a study of Planck Sunyaev-Zel'dovich effect selected galaxy cluster candidates (from their 2013 data release) using the Pan-STARRS imaging telescope in Hawaii. We were able to confirm about 60 galaxy clusters and measure the photometric redshifts with an accuracy of about 2.2%. The second half of the talk will discuss the practical implications of the line of Shapiro delay of gravitational waves, results from GW150914 and will discuss the relevance of Shapiro delay for the detection of EM counterparts of GW sources.

Expeditions for Physics Beyond the Standard Model : Challenges and Prospects

Date: 2017-03-16
Speaker: Dr. Satyanarayan Mukhopadhyay
Venue: Room No. 469

Abstract

The energy, intensity and cosmic frontiers constitute the three major directions of research in particle physics, driven by a large number of ongoing and upcoming experimental and observational probes. Efforts to explore physics beyond the standard model at these experiments give rise to two challenging tasks : (1) how to dig out a tiny signal from a huge background using our understanding of known physics and (2) how to interpret the experimental results from a vast range of probes within an unified theoretical framework. I shall describe progress in addressing the first challenge using examples from the search for strongly interacting new particles at the LHC in difficult to access kinematic regimes. On the second challenge, I shall take up the case-study of classifying and understanding the different probes of particle dark matter, both within the framework of effective field theory as well as in specific simple models.

Heavy quark dynamics in RHIC and LHC

Date: 2017-02-17
Speaker: Dr. Santosh Kumar Das
Venue: Room No. 469

Abstract

The heavy quarks, charm and bottom, constitutes a unique probe of the quark gluon plasma (QGP) properties. Both at RHIC and LHC energies a puzzling relation between the nuclear modification factor RAA(pT) and the elliptic flow v2(pT) related to heavy quark has been observed which challenged all the existing models. We discuss how the temperature dependence of the heavy quark drag coefficient is responsible to address for a large part of such a puzzle along with the full solution of the Boltzmann collision integral for the momentum evolution of heavy quarks in the medium. Ultra-relativistic Heavy-Ion Collision (HIC) also generates very strong initial magnetic field. Since the heavy quark are produced at the early stage of HICs, we argue that their dynamics will be affected by such a strong magnetic field and we demonstrate that the directed flow, v1 , of heavy quarks is a superior probe to estimate the magnetic field generated in non- central HICs. We show that the resultant effects entail a significantly large v1 of charm quarks which is about two order of magnitude larger than the light quarks v1 and can be measured at experiments.

MANY BODY ASPECTS OF GRAVITY IN COMPACT STARS

Date: 2017-02-09
Speaker: Prof. M. Azam
Venue: Room No. 469

Abstract

Compact stars such as neutron stars and black holes are gravitationally bound many body systems. We investigate the importance of short and long range part of gravity for such systems. From our analysis, we conclude that the true essence of gravity lies with the long range nature of the interaction.

2016

Charged Higgs search prospects in bosonic decays

Date: 2016-12-30
Speaker: Dr. Pankaj Sharma
Venue: Room No. 469

Abstract

Anticipated in the current and future runs of the LHC is the discovery of a charged Higgs which would be an unequivocal evidence for new physics. In this talk, I will review the prospects of the LHC in accessing heavy charged Higgs boson signals in bbW final states, wherein the contributing channels can be H \to tb, hW, HW and AW. In particular, we devise a selection strategy which optimizes their global yield. We consider a 2-Higgs Doublet Model Type-II and we assume as production mode bg → tH− + c.c., the dominant one over the range MH ≥ 480 GeV, as dictated by b → sγ constraints. We further make use of jet substructure techniques for Higgs tagging and multivariate techniques such as boosted decision trees in order to maximize the discovery potential of charged Higgs in its bosonic decays.

Mixed fermion dark matter, neutrino mass and collider signature

Date: 2016-12-29
Speaker: Dr. Narendra Sahu
Venue: Room No. 469

Abstract

The galaxy rotation curve, gravitational lensing and the existence of large scale structure imply that the present Universe is filled with a mysterious form of matter, called “dark matter (DM)”,which is about 27% ( roughly 5 times of visible matter) of the total energy budget. Hitherto the existence of DM is obtained via its gravitational interaction in a large scale, starting from galaxy size. The main challenge at present is to probe the DM in a small scale, typically in an earth bound laboratory. The only information so far we know about DM is its relic density. However, the microscopic structure of DM is completely unknown. Unfortunately the standard model (SM) of particle physics, the best model that describes the fundamental interactions of visible matter, does not accommodate any such particle. In this talk we explore certain aspects of physics beyond the SM to include dark matter as well as non-zero neutrino mass, confirmed by oscillation experiments. In particular, we extend the SM by including a mixed singlet-doublet fermion dark matter and obtain the parameter space for testing the hypothesis at collider.

Topological condensed matter physics wins Nobel

Date: 2016-11-10
Speaker: Navinder Singh and Namit Mahajan
Venue: Room No. 469

Abstract

David Thouless, Duncan Haldane and Michael Kosterlitz have won the 2016 Nobel Prize in Physics for their theoretical explanations of strange states of matter in two-dimensional materials, known as topological phases. The trio’s work in the 1970s and 1980s laid the foundations for predicting and explaining bizarre behaviours that experimentalists discovered at the surfaces of materials, and inside extremely thin layers. It is the Kosterlitz-Thouless phase transition, topological explanation of the quantum Hall effect, and the topological band theory that originates from the Haldane chains that form the basis for the Nobel prize. We will explain, in simple language, the physics behind these topics. In the end, we will also present brief biographical sketches of these great men of science.

Breaking of longitudinal relativistic plasma waves and fourth order finite volume numerics for simulating accretion disks

Date: 2016-10-14
Speaker: Mr. Prabal Singh Verma
Venue: Room No. 469

Abstract

One of the major challenge in particle acceleration experiments is to achieve very high energetic charged particles. These high energetic particles are being used in cancer therapy, cutting and melting of hard materials and in understanding high energy physics problems. In conventional accelerators the accelerating electric field can not go beyond a few hundred MV/m due to the breakdown of the material. On the contrary, plasma which already is a broken state of matter can support extremely high electric field (TV/m) in the form of electrostatic plasma waves[2–9]. These waves can be excited as wakefields by sending a laser/particle beam pulse in to the plasma. Amplitude of such plasma waves is limited by a phenomenon called wavebreaking which transforms the coherent electrostatic energy of the wave into the random kinetic energy and thus damps the wave[1]. Therefore, understanding of wavebreaking criteria for plasma waves is important because it can significantly affect the maximum achievable energy in wakefield acceleration experiments. In the first part of my presentation I will talk about the the evolution and breaking of longitudinal relativistic plasma waves in a cold plasma [2]. In the second part, I will talk about the high order numerics for simulating accretion disks. Such disks are formed due the accumulation of matter on to a massive central object and the magnetorotational instability (MRI), which just requires a subthermal magnetic field to break the Keplerian flow into turbulence, is believed to be the most likely mechanism behind the accretion process. Most of the studies on the nonlinear development of the MRI rely on numerical simulations due to the inherent difficulties in approaching strongly nonlinear problems analytically. We have adopted shearing-box approximation [12] , where the computational domain is restricted to a region of small radial extent compared to its radial distance from the disk’s center, is a standard and well defined physical model to understand the nonlinear behaviour of the MRI. The existing numerical tools for MRI simulations are in general second order accurate and since second order schemes are known to have high numerical diffusion, we have developed fourth order accurate finite volume shock capturing code [13, 14] to study the nonlinear behaviour of magnetorotational instability (MRI). I will here talk about the issues we have encountered during the development of high precision code.

Novel method to deal off- shell particle in cascade decays

Date: 2016-09-30
Speaker: Mr. Tripurari Srivastava
Venue: Room No. 469

Abstract

I will discuss an algorithm to calculate decay width for cascade decay involving off-shell particles. First I will give you brief introduction to algorithm then I will explain and demonstrate it with some example with different kind of off- shell particles. Finally I will discuss some works still to be done in this context.

Revisiting the Pauli paramagnetism and the Landau diamagnetism in metals

Date: 2016-09-15
Speaker: Dr. Navinder Singh
Venue: Room No. 469

Abstract

In standard text books on statistical mechanics (Landau-Lifshitz, for example) the calculation of Pauli's paramagnetism is generally performed by neglecting the effect of magnetic field on density of states. However,the criterion of doing so was lacking so far. We work out the criterion of doing so, and thus give the calculation a rigorous foundation. Pauli's calculation is done by three different routes, and so provides a clear understanding. In the strong field limit (\mu_B H> k_B T) it is generally shown that total susceptibility shows de Haas van Alphen (dHvA) oscillations. We point out that even the Pauli paramagnetic susceptibity does show oscillations and a new formula equivalent to Lifshits-Kosevich is derived in terms of Fresnel integrals which goes to the original Pauli result once averaging over the oscillations is performed when low field limit is taken. A new formula in the intermediate temperature regime in terms of PolyLogs is also derived. The effect of electron scattering off bosonic modes on the Lifshits-Kosevich formula is also worked out.

331 Models and Grand Unification: A Step From Minimal SU(5) to Minimal SU(6)

Date: 2016-09-01
Speaker: Mr. Chandan Hati

Abstract

We will discuss the possibility of grand unification of the 331 model.Two possibilities will arise.In SU(6) one can embed the 331 model as a subgroup such that different multiplets appear with different multiplicities.Such a scenario may emerge from the flux breaking of theunified group in an E(6) F-theory GUT.This provides new ways of achieving gauge coupling unification in 331 models while providing the radiative origin of neutrino masses.Alternatively, a sequential variant of the 331 model can fit within a minimal SU(6) grand unification, which in turn can be a natural E(6) subgroup. This minimal SU(6) embedding does not require any bulk exotics to account for the chiral families while allowing for a TeV scale 331 model with seesaw-type neutrino masses.

331 Models and Grand Unification: A Step From Minimal SU(5) to Minimal SU(6)

Date: 2016-09-01
Speaker: Mr. Chandan Hati
Venue: Room No. 469

Abstract

We will discuss the possibility of grand unification of the 331 model. Two possibilities will arise. In SU(6) one can embed the 331 model as a subgroup such that different multiplets appear with different multiplicities. Such a scenario may emerge from the flux breaking of the unified group in an E(6) F-theory GUT. This provides new ways of achieving gauge coupling unification in 331 models while providing the radiative origin of neutrino masses. Alternatively, a sequential variant of the 331 model can fit within a minimal SU(6) grand unification, which in turn can be a natural E(6) subgroup. This minimal SU(6) embedding does not require any bulk exotics to account for the chiral families while allowing for a TeV scale 331 model with seesaw-type neutrino masses.

Curvature perturbations from preheating

Date: 2016-08-24
Speaker: Dr. Arindam Mazumdar
Venue: Room No. 469

Abstract

Transition period between inflation and radiation domination is called reheating. Due to some problems with perturbative reheating a better version of reheating with non-perturbative mechanism was developed whichis known as preheating. Curvature perturbations generated during preheating has been calculated using lattice simulations and analytical formulations. But there had been no analytical approach available which could reproduce the results coming from the numerical simulations. I willpresent a framework for calculating super-horizon curvature perturbation from the dynamics of preheating, which gives a reasonable match to the lattice results. I will also discuss the problem of predicting non-gaussianity in this scenario.

Continuous transitions between quantum and classical systems

Date: 2016-08-04
Speaker: Prof. Partha Ghose
Venue: Room No:469

Abstract

The conventional demonstrations that classical mechanics is a limiting case of quantum mechanics are misleading. The purpose of the talk will be to offer a new equation which provides a continuous link between quantum and classical systems. Examples will be given to show these transitions in a few simple cases. New predictions can be made using this method for mesoscopic systems. *References*: P. Ghose, ``Continuous Transition Between Quantum and Classical Mechanics I'', Found. of Phys. vol 32, 871-892 (2002). P. Ghose and M. K. Samal, ``Continuous Transition Between Quantum and Classical Mechanics II'', Found. of Phys. vol 32, 893-906 ( 2002). W P Schleich, D M Greenberger, D H Kobe and M O Scully, ``A wave equation interpolating between classical and quantum mechanics'', Phys. Scr. vol 90,108009 (2015).

A study of the static and dynamical thermal conductivity of metals and other systems

Date: 2016-07-07
Speaker: Mr. Pradeep Kumar
Venue: Room No:469

Abstract

The Mori?s projection method, known as memory function method is an important theoretical formalism to study various transport coefficients.In the present work, we calculate the dynamical thermal conductivity in the case of metals using the memory function formalism. We introduce thermal memory functions for the first time and discuss the behavior of thermal conductivity in both zero frequency limit and in the case of non-zero frequencies. We compare our results for the zero frequency case with the results obtained by the Bloch-Boltzmann kinetic approach and find that both approaches agree with each other. Motivated by some recent experimental advancements, we obtain several new results for the ac or the dynamical thermal conductivity.

Seesaw mechanism of Neutrino mass generation and some TeV scale variants : A review

Date: 2016-06-24
Speaker: Mr. K. Vishnudath
Venue: Room No:469

Abstract

In spite of their weakly interacting nature, we have so far accumulated an enormous amount of knowledge about neutrinos. From neutrino oscillation experiments, we learned a few years ago that neutrinos are massive and flavours are mixed. However, we still do not know the absolute values of their masses. Seesaw mechanism is considered to be one of the most natural approach toward understanding the sub-eV neutrino mass scale. In my talk,I will review the seesaw mechanism of neutrino mass generation and some of its proposed TeV scale variants, including seesaw mechanisms in Left-Right symmetric models.

Looking for T-violation in B decays

Date: 2016-06-23
Speaker: Ms. Bharti Kindra
Venue: Room No:469

Abstract

Since the discovery of CP violation in neutral K, and B meson system, experiments have questioned the existence of T violating effects as well.In 2012, direct time reversal violation was observed for the first time at asymmetric B factory PEP-II where an entangled B-Bbar state is produced.CP and flavour specific final states are employed to identify the initial state quantum numbers and properties, which are then used to study the T-conjugated processes. Non zero results showed that T is indeed violated independent of Cp violation. In my talk, I will discuss the experiment and the phenomenology used therein, and describe some work that is being done in this direction.

Are there quantum limits to transport in quantum many-body systems?

Date: 2016-04-28
Speaker: Dr. Nandan Pakhira
Venue: Room No. 469

Abstract

ABSTRACT --------------- Good metals like copper and gold are characterised by diffusive transport of coherent quasi-particle states. The electrical resistivity (ρ)which characterises charge transport in these materials is well within the Mott-Ioffe-Regel (MIR) limit, ha/e2(where a is the lattice constant) i. e. (ρ << milli-Ω cm). Also the shear viscosity (η) which characterises momentum transport is also bounded, i. e., η << nħ/5(where n is the density of electrons) in the quasi-particle regime of transport. But in a wide range of strongly correlated materials and most notably in the strange metal regime of doped cuprates (high-Tc superconductors) the resistivity exceds the MIR limit and the picture of coherent quasi-particle based transport breaks down. Recently, a holographic duality (AdS/CFT correspondence) based approach in string theory led to a proposed universal lower bound η/s ≥ħ/4π kB for the ratio between the shear viscosity (η) and the entropy density (s). This bound is found to be valid in a wide class of classical fluids like water and quantum fluids including the quark-gluon plasma in the Relativistic Heavy Ion Collider (RHIC) and cold atomic fermionic gases in the unitary limit of scattering. Also, loosely motivated by holographic duality, and inspired by the quantum bound to η/s Hartnoll proposed a lower bound to the charge diffusion constant D ≥ ħvF2/kB T the incoherent regime of transport [2], where vF is the Fermi velocity and T the temperature. Using dynamica mean field theory (DMFT) we calculate the diffusion constant and shear viscosity in the single band Hubbard model. We explore possible violation of Hartnoll's proposed bound [3] and possible existence of quantum bounds in the shear viscosity (η) entropy density (s) ratio in the incoherent regime of transport [4].

Top FCNC decays in the aligned two-Higgs doublet model

Date: 2016-03-29
Speaker: Dr. Gauhar Abbas
Venue: Room No. 469

Abstract

We compute the flavour-changing top decays t -> ch and t -> cV (V =g ,Z)within the framework of the aligned two-Higgs-doublet models. By exploiting constraints fromflavour physics and themeasured Higgs properties, we investigate the parameter space of the modeland its impact on theassociated branching ratios. It is observed that the Higgs signal strengthin the di-photon channelimposes important restrictions on the t -> ch decay rate when the chargedscalar of the model islight. We conclude that the rates of these flavour-changing top decays are beyond the expected sensitivity of the future high-luminosity phase of the LHC.

Neutrino Mass Models at the LHC

Date: 2016-02-25
Speaker: Prof. Frank Deppisch
Venue: Room No. 469

Abstract

Models of neutrino mass generation provide well motivated scenarios of Beyond-the-Standard-Model physics. The synergy between low energy and high energy LHC searches facilitates an effective approach to rule out,constrain or ideally pinpoint such models. In my seminar, I will provide a brief overview of scenarios where searches at the LHC can help determine the mechanism of light neutrino masses and potentially falsify baryogenesis mechanisms.

Monojet constraints for the 750 GeV diphoton resonance

Date: 2016-02-16
Speaker: Dr. Suchita Kulkarni
Venue: Room No. 469

Abstract

The recent announcement of a mild excess in diphoton channel around 750 GeV has generated a lot of excitement. I will exemplify phenomenology a simplified model containing a scalar resonance coupling to gluon, photon and dark matter particle. I will describe constraints due to existing dark matter monojet searches on this parameter space. If the resonance is confirmed in the next round of data taking, the simplified model considered here will be either ruled out or lead to insights into the scale of new physics.

Mercury monohalides: promising new candidates for search of the electron electric dipole moment

Date: 2016-01-29
Speaker: Srinivasa Prasannaa
Venue: Room No. 469

Abstract

Heavy polar diatomic molecules are the primary tools for searching for the P and T-violating electric dipole moment of the electron (eEDM). Valence electrons in some molecules experience extremely large effective electric fields, which are crucial to the success of polar-molecule-based eEDM search experiments. In this talk, we report on the results of relativistic ab initio calculations (using the relativistic coupled cluster method) of the effective electric fields in a series of molecules that are highly sensitive to an eEDM, the mercury monohalides (HgF, HgCl, HgBr,and HgI). We identify HgBr and HgI as attractive candidates for future electric dipole moment search experiments. We also discuss why these molecules have such large effective electric fields.

A Lorentz covariant local theory of fermions with mass dimension one

Date: 2016-01-21
Speaker: Prof. Dharam Vir Ahluwalia
Venue: Room No. 469

Abstract

In this informal seminar I will construct eigenspinors of the charge conjugation operator for spin one half and show that they do not satisfy Dirac equation. This has been known for about a decade now. The new result that I'll present is on constructing a mass dimension one fermionic field. Reference: http://arxiv.org/pdf/1601.03188

Top Physics in the LHC Era

Date: 2016-01-12
Speaker: Dr. Pankaj Sharma
Venue: Room No. 469

Abstract

The ultimate goal of the Large Hadron Collider (LHC) is to reveal the secrets of electroweak symmetry breaking (EWSB) and discover the new physics beyond the Standard Model (SM) of particle physics. The top quark has been believed to be a key to uncover the veil over EWSB and new physics. The top quark is unique in the sense that it decays before it can form a bound state and thus allows a possibility to measure its polarization. In this seminar, I will discuss various ways to measure the top quark polarization and its usefulness in constraining various new physics models at the LHC. I will also discuss how the top quark can be utilized to characterize the properties of the newly discovered Higgs boson at the LHC. Also, excesses have been seen in the charged-Higgs boson searches at CMS at around 250 GeV and 500 GeV massese in the 13 TeV data which point to a very fat charged Higgs. I will also discuss how this can be explained in the purview of type-II 2HDM.

The axial U(1) anomaly and topological structures in finite temperature QCD

Date: 2016-01-11
Speaker: Dr. Sayantan Sharma
Venue: Room No. 469

Abstract

The magnitude of axial U(1) symmetry breaking is believed to affect nature of Nf = 2 QCD chiral phase transition. The explicit breaking of chiral symmetry due to realistic light quark masses is small hence it is important to use fermions which do not break chiral symmetry on the lattice, to understand the fate of axial U(1) near the chiral crossover temperature, Tc. I discuss on our recent study of the eigenvalue spectrum of QCD with two different lattice fermion discretizations which retain a remnant of the continuum chiral symmetry. Studying the eigenvalue spectrum we do not observe any hints of the effective restoration of axial U(1) near Tc. A pile up of the near-zero eigenmodes is observed to persist even at 1.5Tc which are primarily responsible for its breaking. These eigenmodes are localized unlike those in the bulk, with a mobility edge similar to a Mott-Anderson like system. The origin of such near-zero mode spectrum can be traced back to the dilute instanton gas ensemble already setting in at 1.5 Tc. Our study for the first time also investigates in great detail the topological structures in QCD just near the chiral crossover transition from the data for topological susceptibility. I also discuss the consequences of our results for topological susceptibility in QCD for the prediction of the amount of axion dark matter.

Consequences of f(R) gravity in Randall?Sundrum Model

Date: 2016-01-08
Speaker: Dr. Sampurnanad Jha
Venue: Room No. 469

Abstract

One of the vexing issues of the standard model of particle physics is to explain the disparity between the Planck scale and the electroweak scale. An interesting approach due to Randall Sundrum (RS), does explain the discrepancy by assuming a 4+1 dimensional world. In this model, extra dimension is compactified on a circle whose upper half is identified with the lower half and the known world is confined to one of a pair of three-branes that sit atop the two fixed points. However, the value of the compactification radius is treated as a model parameter and not determined by the dynamics of the model. Such a degree of freedom violates the equivalence principle. We point out that the corrections to the gravity sector of the Einsein-Hilbert action can lead to scalar degree of freedom which, interacting with the radius field (modulus), results in an effective potential for it. The effective potential thus obtained is minimized to set a value of compactification radius. We show that for reasonable values of model parameters, the hierarchy between the Planck scale and the electroweak scale can be explained in a modulus stabilized scenario. Further, we also discuss that the scalar field, that arises naturally in our model, can be used to explain the magnetic field present on cosmological scale.

Recent developments on Gravitational Collapse Final States

Date: 2016-01-07
Speaker: Prof. Pankaj Joshi
Venue: Room No. 469

Abstract

The final fate of massive collapsing matter clouds and their dynamical evolution has been a fundamental topic in black hole physics and its applications to relativistic astrophysics for the past many years. While the general theory of relativity predicts a necessary occurrence of a space-time singularity in such a scenario, the formation of event and apparent horizons in gravitational collapse is very much a subject of current investigations. In fact, it is the formation and behaviour of the apparent horizon that decides whether the singularity of collapse is enveloped in a black hole or whether it may be visible for far away observers in the space-time. We point out that the apparent horizon and trapped surface formation is determined in terms of the initial data for collapse and the allowed evolutions by the Einstein equations. The black hole and naked singularities in gravitational collapse involve key open issues such as genericity and stability aspects related to these outcomes. We shall discuss some of these issues, including recent implications for astrophysics such as the nature and structure of accretion disks around black holes and singularities and very high energy particle collisions around these objects.

Quantum Information Processing: Implementation Schemes and Quantum Memory

Date: 2016-01-01
Speaker: Dr. Sandeep Goyal
Venue: Room No. 469

Abstract

The central aim of the quantum information processing (QIP) is to extend information processing (including computation and communication) in regimes where quantum effects are significant. QIP uses the states of a multilevel quantum system as the basic unit of information. To be useful, a quantum system needs to be both isolated from its environment and easy to control, thus placing a stringent requirement on its physical realization. Photons interact weakly with their environment and are in this respect suitable candidates for QIP. In this talk, I will present photonic implementation schemes for a number of QIP tasks. While some of the QIP tasks such as quantum walks, can be implemented using intense laser pulses (classical light), other protocols such as quantum teleportation, require reliable on demand single photon sources. Quantum memories, i.e., systems capable of storing a single photon, can be used to develop a single-photon source. Hence, constructing efficient and robust quantum memories would pave the way for performing QIP tasks efficiently. Here I will show that quantum memory consists of atomic frequency combs, beside storing a single photon efficiently, can be used for creating genuine multipartite entangled states in macroscopic systems. Finally, I will present an experimentally accessible method to witness this entanglement.

2015

Detecting Dipolar Dark Matter in Beam Dump Experiments

Date: 2015-12-29
Speaker: Dr. Soumya Rao
Venue: Room No. 469

Abstract

We study interaction of low mass dark matter within beam dump experiments. In particular we study the dipolar dark matter model which assumes that the dark matter couples to Standard Model particles via its electric or magnetic dipole moment. We analyse the constraints on this model in the context of a particular beam dump experiment E613 conducted in the Fermilab. We compare the bounds from other experimental data, such as helioseismological data and direct detection experiments.

Physics with ultra high energy neutrinos

Date: 2015-12-28
Speaker: Dr. Sushant Raut
Venue: Room No. 469

Abstract

The IceCube experiment at the South Pole has been constructed to observe ultra high energy neutrinos. These neutrinos, which arrive from extra-galactic sources, have energies in the TeV-PeV range and beyond. A study of these neutrinos complements the neutrino data collected by solar, atmospheric, reactor and accelerator-based neutrino beams. This talk discusses the analysis of IceCube data in the context of CP violation and neutrino decay. For specific source flavour ratios of astrophysical neutrinos, we present our fit to the CP-violating phase. Further, our analysis places constraints on the flavour ratio of astrophysical neutrinos. We also discuss the bounds that can be placed on neutrino decay lifetime.

IF THERE IS HEAVEN ON EARTH

Date: 2015-12-07
Speaker: Prof. Biswarup Mukhopadhyaya
Venue: Room No. 469

Abstract

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Making Gravity maps with satellite borne Atomic Clocks

Date: 2015-11-10
Speaker: Prof. Subhendra Mohanty
Venue: Room No. 469

Abstract

Gravity maps over a terrain give information of the underground density variations and can be used to map subterranean acquirers, hydrocarbon and mineral deposits. The advances in the accuracy of atomic clocks is now such that General Relativistic corrections to Newtons gravity are measurable and these can be used to make accurate maps of "Geoid Anomalies" or local subterranean density variations. As a byproduct, accurate measurements of atomic frequency shifts in the gravitational field of the Earth can be used to test Einstein's General Relativity. This talk is a theory backup of the GMAP (Gravity Map) proposal which the Theory Division is putting forward for approval in the next plan.

Degenerate Supersymmetry

Date: 2015-11-02
Speaker: Dr. Ketan Patel
Venue: Room No. 469

Abstract

A degenerate supersymmetric particle spectrum can escape constraints from flavor physics and at the same time evade limits from the direct searches. I will discuss various indirect constraints and phenomenological aspects of such a possibility.

Fun with Phases

Date: 2015-10-27
Speaker: Dr. Ipsita Mandal
Venue: Room No. 469

Abstract

We discuss some interesting classical and quantum phase transitions. The classical 2d spin 1 Blume-Capel model is a non-integrable model, but it exhibits a tricritical point described by a CFT which can be located only numerically. We show how we can determine this point using the concepts of Entanglement entropy, employing classical Monte Carlo simulations coupled with the knowledge that the critical theory is a minimal model with c=0.7. In the next part, we discuss topological phases. Certain real parameters of a Hamiltonian, when continued to complex values, can give rise to singular points called exceptional points (EP's), where two or more eigenvalues coincide and the complexified Hamiltonian becomes non-diagonalizable. We show that for a topological superconductor with a chiral symmetry, one can find EP's associated with the chiral zero energy Majorana fermions bound to a topological defect/edge. Exploiting the chiral symmetry, we propose a formula for counting the number (n) of such chiral zero modes. We also establish the connection of these solutions to the Majorana fermion wavefunctions in the position space. Finally, we conclude that EP's cannot be associated with the Majorana fermion wavefunctions for systems with no chiral symmetry, though one can use our formula for counting n, using complex k solutions where the determinant of the corresponding BdG Hamiltonian vanishes.

Wigner distributions of quark

Date: 2015-10-15
Speaker: Dr. Sreeraj Nair
Venue: Room No. 469

Abstract

Wigner distribution functions are quasi-probabilistic functions that can provide simultaneous information about the distribution in the momentum and position space. We study the Wigner distribution of quark and gluon in the dressed quark model. We also calculate the kinetic and canonical orbital angular momentum of quark and gluon in this model.

Unravelling Medium Effects in Heavy Ion Collisions with jets

Date: 2015-10-08
Speaker: Dr. Rishi Sharma
Venue: Room No. 469

Abstract

We propose a new observable to analyze events with jets in heavy ion collisions. The observable measures how a thermal medium affects the multiplicity and distribution of energetic particles in a jet. Using few known models for energy loss and jet quenching, we demonstrate its capability to distinguish the physics of these models.

Properties of Quark-Gluon-Plasma produced in relativistic heavy ion collisions

Date: 2015-09-24
Speaker: Dr. Vinod Chandra
Venue: Room No. 469

Abstract

There are strong indications that relativistic heavy ion collision experiments at BNL/LHC (CERN) have produced the hottest and the most liquid state of the matter. In fact, the shear viscosity to entropy density ratio for the matter there, turns out be the lowest among all the known fluids. This state of the matter is commonly known as quark-gluon-plasma (QGP). At the theoretical front, its existence can be attributed to the confinement-deconfinement phase transition in Qunatum Chromodynamics (QCD: the underlying theory of the strong interaction). The QGP is expected to exist a few micro-second after the big-bang. Relativistic dissipative hydrodynamical modeling of the space time evolution of the QGP has been highly successful in understanding the physics of the strong interaction. The shear viscosity, bulk viscosity, of the QGP and the equation of state (computed using lattice QCD/improved pQCD) need to be specified at the beginning of the hydrodynamical evolution of the QGP. The prime focus will be on the understanding of shear and bulk viscosities of the QGP from the view point of transport theory. We shall also highlight the impact of these viscosity coefficients on the physics of the strong interaction.

Supercomputing the properties of quark gluon plasma

Date: 2015-09-15
Speaker: Dr. Prasad Hegde
Venue: Room No. 469

Abstract

Lattice QCD is the study of QCD, the theory of the strong force, in its non-perturbative regime through the use of powerful supercomputers. In this talk, I will describe its application to the study of the properties of the quark-gluon plasma, which is a new state of matter created through the collision of heavy nuclei. Here, lattice QCD can not only provide quantitative estimates of the pressure, energy density, etc. but, by varying the quark masses for example, also shed light on the nature and order of the phase transition. Recently, the RHIC experiment at Brookhaven Lab launched its Beam Energy Scan program. The goal of this program is to look for the famous QCD critical point that is conjectured to exist at some moderately large value of the chemical potential. We believe that lattice QCD can make important contributions to this program. I will touch upon some of our recent results in this context and describe what should be possible to do in the near future.

Developing of an optical clock using trapped Ytterbium-ion

Date: 2015-09-10
Speaker: Dr. Subhadeep De
Venue: Room No. 469

Abstract

Increasing accuracies of the atomic clocks have wide range of applications in various fields ranging from sophisticated technologies to precision experiments. Now-a-days the state-of-the-art atomic clocks based on forbidden optical transitions has achieved an accuracy of ~10-18, which means 1 s inaccuracy over the age of the universe. Recently we have started developing an atomic clock that will operate at the |2S1/2; F=0, mF=0> - |2F7/2; F=3, mF=0> octupole transition at wavelength 467 nm of a single trapped and laser cooled ytterbium-ion. We will use an electrodynamic (Paul) trap of the end cap geometry for trapping a single ion and perform precision frequency measurements. We have fabricated a prototype of the trap using the design parameters that we have opted through numerical simulations. We have also estimated systematic uncertainties that are expected from our experiment. As of now, we have designed the ion trap, the ultra-high vacuum chamber and optics associated to the laser cooling. We have already fabricated some sub-components of the experiment such as electromagnetically shielded helical resonator for delivering the radio frequency to the trapping electrodes, atomic oven for producing nearly collimated ytterbium atomic beam and various electronic modules. Current status of the experiment and plans will be discussed.

Principle of Least Action in General Relativity

Date: 2015-09-03
Speaker: Mr. Sumanta Chakraborty
Venue: Room No. 469

Abstract

Constructing a well-posed variational principle and characterizing the appropriate degrees of freedom that need to be fixed at the boundary are non-trivial issues in general relativity. I will discuss a few toy examples in classical mechanics and field theory before going into general relativity. For spacelike and timelike boundaries I will show that the action principle for general relativity is well posed, only when a suitable counter-term [the Gibbons-Hawking-York (GHY) counter-term] is added to the action principle. Also I will show that the degrees of freedom to be fixed on the boundary are contained in the induced 3-metric. These results, however, do not directly generalize to null boundaries on which the 3-metric becomes degenerate. In this talk I will address the following questions: (i) What is the counter-term that may be added on a null boundary to make the variational principle well-posed? (ii) How do we characterize the degrees of freedom which need to be fixed at the null boundary?

Confinement Transition in QCD: Phenomenology and Early Universe Impilcations

Date: 2015-08-20
Speaker: Dr. Abhishek Atreya
Venue: Room No. 469

Abstract

Quantum Chromodynamics (QCD) is the theory of strong interactions, responsible for the binding of nucleus and nucleons as well. One of the peculiar property of QCD is the confinement of `color' charge. The finite temperature formulation of theory predicts a transition from a confined phase to a deconfined phase (Quark Gluon Plasma) at extreme temperature and baryon chemical potential. The phase structure of QCD is very rich owing to its non-abelian nature. Roughly half of the talk would be devoted to provide a brief introduction to the phase structure of QCD, and the onging experimental endeavour to probe it, in a language (hopefully) accessible to non specialists. The later half will be based on the study of QCD Z(3) domains which arise naturally while discussing the confinement-deconfinement phase transition using a Landau-Ginzburg kind of effective potential. We will explore the possibility of spontaneous CP violation in the scattering of quarks and anti-quarks from QCD Z(3) domain walls. This finds interesting implications in Cosmology and also in Heavy Ion Collisions. In context of early universe, we study the effect of this spontaneous CP violation on the baryon transport across the collapsing large Z(3) domain walls (which can arise in the context of certain low energy scale inflationary models). If time permits, then we'll also discuss the quark scattering from Z(3) walls by including the effects of dynamical quarks. This leads to interesting changes in the quark scattering from the Z(3) interfaces.

Search for gravitational waves from binary blackholes using multi-detector geometrical coincidence

Date: 2015-07-30
Speaker: Dr. Gurudatt Gaur
Venue: Room No. 469

Abstract

Coalescing compact binary consisting of neutron star and/or black hole are the most promising sources of gravitational waves, to be detected by ground-based interferometric detectors like, LIGO, Virgo, GEO, TAMA etc. Data Analysis for the detection of gravitational waves from these sources comprises of a sequence of jobs such as place a template bank, filter the data, do coincidence, etc. We develop a method to determine coincidence among the triggers from various detectors using a metric caculated in the space of IMRPhenomB waveform family. In this talk, I shall discuss the advantages of using this metric in the search of gravitational waves from binary black hole systems in LIGO data.

Electromagnetic instability induced by Neutrino interaction

Date: 2015-07-24
Speaker: Mr. Manu George
Venue: Room No. 469

Abstract

Interaction of lepton with neutrino can modify the lepton wave function. As a result, the presence of neutrino can indirectly modify the photon polarization tensor. It was observed in field theoretical calculations that, left-right asymmetry in neutrino density can contribute to an anti-symmetric term in the photon polarization tensor. In this talk I shall try to construct kinetic theory from non-relativistic Hamiltonian for a spin half system in the presence of neutrino background. I shall also calculate the current and polarization tensor using this kinetic theory.

Instabilities in chiral hydrodynamics

Date: 2015-07-23
Speaker: Mr. Manu George
Venue: Room No. 469

Abstract

Parity violating effects arises from quantum anomalies, play an important role in wide range of areas in physics, from quantum Hall system to cosmology. Chiral magnetic effect(CME) is one of such phenomena arises in the presence of a magnetic field, due to the asymmetry between left-handed and right-handed particle, parameterized by chiral chemical potential μ_5 ≡μ_R − μ_L. The production of huge magnetic field(~10^18 G)in the off central heavy-ion collisions set up an experimental platform for the observation of CME. Recently kinetic theory and hydrodynamics are appropriately modified to describe these quantum anomalies and CME. In this talk I shall briefly discuss about the chiral kinetic theory and linear analysis of chiral hydrodynamics.

Improving hadron resonance gas model

Date: 2015-07-23
Speaker: Mr. Guruprasad Prakash Kadam
Venue: Room No. 469

Abstract

Albeit the canonical non interacting hadron resonance gas (HRG) model is successful in describing (the thermodynamics of) hadronic phase of quantum chromodynamics, it ignores two important features of hadronic matter; that there exist short range repulsive interaction between hadrons and hadron masses are depends on temperature (and baryon density) which is rather upshot of the chiral symmetry. In this seminar I will discuss our current endeavour to improve the canonical non-interacting HRG model with an equation of state accounting for the repulsive interaction between hadrons as well as temperature (and density) dependent hadron masses.

Primordial magnetic field and kinetic theory with Berry curvature

Date: 2015-07-22
Speaker: Mr. Arun Kumar Pandey
Venue: Room No. 469

Abstract

Magnetic fields have been observed not only on small scale but also on large scale of the universe. Depending on the length scale, strength of the magnetic field varies. They play an important role in the formation of astronomical environments like plasma and currents. However it is still not clear from where and how they came into existence. It is usually assumed that the observed magnetic fields were amplified by dynamo mechanism from preexisting seed magnetic fields coherent over scales of the order of 100 Mpc at the time of structure formation. But recent observation suggests that, these seed fields may have generated very early in the universe. In this talk, I shall discuss about generation of Primordial magnetic field using chiral kinetic theory at temperature T> 80TeV.

Excitation spectrum and dispersion relation of binary condensates in quasi-2D optical lattices

Date: 2015-07-22
Speaker: Mr. Kuldeep Suthar
Venue: Room No. 469

Abstract

In this talk, we explore the collective excitations of two-species Bose-Einstein condensates (TBECs) loaded into two-dimensional optical lattices. We develop the Hartree-Fock-Bogoliubov theory with the Popov approximation using the coupled discrete nonlinear Schrodinger equations to analyze the quasiparticle mode evolution of TBEC. We observe the transition from miscible to the immiscible (phase-separated) ground state density profile upon varying the intraspecies (interspecies) interaction for 87Rb-85Rb (133Cs-87Rb) TBEC. At phase separation, the degenerate slosh mode goes soft and gets transformed into an interface mode. This mode regains energy upon further change in the interaction strength. We shall also discuss the character of the excitations using dispersion relation of TBEC in harmonically trapped optical lattices.

Black Holes in Our Universe

Date: 2015-07-20
Speaker: Dr. Prateek Sharma
Venue: Room No. 469

Abstract

Once a figment of theorists' imagination, Black Holes (BHs) are now astronomically well-established entities. Astrophysical BHs occur in two varieties: supermassive BHs (10^6-10^9 solar mass) at the centers of galaxies and stellar-mass BHs (~10 solar mass) in form of X-ray binaries. I will present astrophysical evidence for BHs, and present theoretical models to understand accretion of matter on to BHs in different conditions. BHs, owing to their strong gravity, are powerful engines which strongly influence their surroundings through mechanical energy (in form of jets) and intense radiation. I will also discuss the central role of supermassive BHs in controlling galaxy formation.

Asymmetries in the angular distribution of rare decay Lambda_b --> \Lambda (--> N \pi) l+ l-

Date: 2015-07-16
Speaker: Mr. Girish Kumar
Venue: Room No. 469

Abstract

The semi-leptonic decay Lambda_b --> \Lambda (--> N \pi) l+ l- is mediated by electro-weak loop diagrams in Standard model (SM) and can receive large enhancements from new physics (NP). It gives access to a variety of angular observables and hence offers a rich phenomenology. From the theoretical point of view, exclusive modes suffer from large hadronic uncertainties due to the form factors. One has to find strategies to reduce this form factor dependence by considering certain ratios. In this talk, we start by discussing the angular distribution of the final sate of this decay mode. We discuss angular asymmetries which can be extracted to completely determine this distribution. We then discuss the- important angular observables and appropriate ratios of these angular asymmetries which can be used to test SM.

Dynamics of a Travelling Front

Date: 2015-07-09
Speaker: Prof. Debashis Ghoshal
Venue: Room No. 469

Abstract

Systems with an unstable (metastable) phase and a stable one are often separated by a sharp `wall'. As the size of the region of stability grows, this wall moves as a `travelling front', which may have characteristic universal properties in certain cases. In this talk we will briefly discuss the early history of the travelling front, and then describe a non-local variant that we encountered and studied.

Plausibility of low scale Left-Right symmetry

Date: 2015-07-03
Speaker: Prof. Urjit Yajnik
Venue: Room No. 469

Abstract

The smallness of neutrino masses raises the hopes of links to a high energy scale through the see-saw mechanism. However, the value of the higher mass scale can vary from the GUT scale down to the TeV scale. We explore the scenario that the higher scale is close to the TeV scale and possibly manifest at LHC or a future collider. It is shown that using mostly arguments of symmetry and the viability of standard cosmology provides sufficient constraints to determine how low the scale can be. This is realised specifically using a supersymmetric implementation of Left-Right symmetry. It shown in this case that leptogenesis always remains viable and places no restriction on the scale of symmetry breaking. It is shown that Gauge Mediated Symmetry Breaking may also be communicating L<-->R parity breaking.

Dissipative properties of hot and dense matter in excluded volume hadron resonance gas model

Date: 2015-07-02
Speaker: Guruprasad Prakash Kadam
Venue: Room No. 469

Abstract

Matter created in Relativistic Heavy Ion Collider i.e quark gluon plasma (QGP), is "the most perfect" fluid found in nature. Although "the most perfect fluid" implies zero viscosity, QGP has non zero shear viscosity(5 × 10^11 Pa·s). Indeed, based on anti-deSitter-conformal field theory (AdS/CFT) correspondence, Kovtun-Son-Starinets conjectured that no fluid found in nature can have shear viscosity to entropy ratio less that 0.08. This bound is famous KSS bound. However, in our recent work based on relativistic kinetic theory, we found that a simple system consisting of gas of hard spheres hadrons, KSS bound is violated if the gas is sufficiently dense. In this seminar I will discuss these results of the kinetic theory within the limitations of the theory.

Weighing and reconstructing new physics mass and events at LHC

Date: 2015-06-18
Speaker: Abhay Kumar Swain
Venue: Room No. 469

Abstract

After successful discovery of the Higgs boson, the Large Hadron Collider (LHC) would confront the major challenge in searching for new physics and new particles. Any such observation necessitates the determination of mass and other quantum numbers like spin, polarisation etc. Many of our theories beyond the Standard Model (BSM) motivated from profound experimental indication of dark matter (DM), trying to accommodate them as some stable BSM particles within these theory. In such scenario, any production of heavy resonance of new particles eventually decay semi-invisibly resulting at least two stable particles in the final state. Reconstruction of these events at hadron colliders together with the mass determination of DM or intermediate particles is challenging and center to this talk. In this talk I will discuss some mass restricting way that can lead us to determine the new particle mass when it decays semi-invisibly. I will also present a new method which can be used for the full reconstruction of the event in the above scenario.

Gauge mediated supersymmetry breaking in the light of HIggs

Date: 2015-05-05
Speaker: V Suryanarayana Mummidi
Venue: Room No. 469

Abstract

In this talk, I review aspects of Minimal Gauge mediated supersymmetry breaking models and discuss its phenomenological status in the light of much celebrated discovery of CP even Higgs scalar at the LHC. I present few viable extensions of mGMSB models in the context of supersymmetry breaking.

Suppression of phase separation in warm condensate mixtures

Date: 2015-04-30
Speaker: Mr. Arko Roy
Venue: Room No. 469

Abstract

We shall discuss about the role of thermal fluctuations in binary condensate mixtures of dilute atomic gases. We use Hartree-Fock-Bogoliubov with Popov approximation to probe the impact of non-condensate atoms to the phenomenon of phase-separation in two-component Bose-Einstein condensates. We demonstrate that, in comparison to $T=0$, there is a suppression in the phase-separation of the binary condensates at $T\neq0$. This arises from the interaction of the condensate atoms with the thermal cloud. We also show that, when $T\neq0$ it is possible to distinguish the phase-separated case from miscible from the trends in the correlation function. However, this is not the case at $T=0$.

Model of multi magnetic flux tube configurations in the Lower Solar Atmosphere

Date: 2015-04-10
Speaker: Dr. Viktor Fedun
Venue: Room No. 469

Abstract

In this talk we will show the possibility of analytical construction of realistic magnetic field configurations, typical of the lower solar atmosphere. The magneto-hydrostatic equilibrium is obtained by taking into account the presence of external forces. Systems incorporating open single and multiple flux tubes and closed magnetic loops can be combined to form magnetic structures that could even represent complex solar active regions. The developed model successfully spans the Interface Region of the solar atmosphere, from the photosphere up to the solar corona across the challenging transition region, while retaining physically valid plasma pressure, density and magnetic flux. Modelling magnetic structures can depict the main characteristics of solar intergranular lanes or active regions. HMI data can be used, as an initial magnetic field distribution, to construct a realistic magnetic field distribution. The model includes a number of free parameters, which makes the solution applicable to a variety of other physical problems, and it may therefore be of more general interest.

Properties, simulations, and results of perovskite materials at finite temperatures

Date: 2015-04-09
Speaker: Dr. Brajesh K. Mani
Venue: Room No. 469

Abstract

Perovskite materials are of considerable interest both fundamentally as well as for their potential technological applications reasons. One of the many great fascinating properties of these materials is that they can display a variety of structural phase transitions, such as ferroelectric, ferromagnetic, antiferrodistortive, antiferroelectric, antiferromagnetic, and in some cases a combination of two or even more of these. An accurate prediction and comparison of these properties with experiments requires estimation at finite temperatures, but is beyond the scope of density functional theory. An approach based on a microscopic effective Hamiltonian makes these studies possible. The parameters in the effective Hamiltonian are determined from first-principles calculations and used in the framework of Molecular Dynamics and/or Monte Carlo simulations. In this seminar, after providing a brief introduction to the simulation methods, I will discuss our simulation results and their technological importance for ferroelectric PbTiO3, antiferroelectric PbZrO3, and multiferroic BiFeO3 materials.

Heavy Ion Physics - basics and some recent results

Date: 2015-03-19
Speaker: Prof. Sourendu Gupta
Venue: Room No. 469

Abstract

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Critical Mass of Neutron Stars: A Black Hole Entropic View

Date: 2015-02-20
Speaker: Prof. Parthasarathi Majumdar
Venue: Room No. 469

Abstract

We begin with a brief summary of extant approaches to understand the observed absence of neutron stars heavier than 2 solar masses. Many of these involve an adaptation of Chandrasekhar?s ideas of a limiting mass for white dwarf stars, based on hydrostatic equilibrium, to situations where general relativity can no longer be ignored. We survey the complications that this might introduce to the already difficult problem of determining the equation of state of this superdense system as an essential part of hydrostatic equilibrium. We then describe an alternative perspective, still under construction, to this problem, based on certain results from the analysis of (quantum) black hole entropy and thermal stability. These results, derived from a non-perturbative, background-independent formulation of canonical quantum gravity, will be discussed in some detail. Some attempts to incorporate entanglement entropy ideas into the construction are also to be discussed. The aim here is a formulation of the issue of neutron star instability in terms of the stability and growth of a nascent quantum horizon deep inside a collapsing neutron star. If this perspective works, this might be a first indirect evidence of quantum gravity playing an important role in the gravitational collapse of neutron stars.

Quantum state discrimination by LOCC (local operations and classical communication)

Date: 2015-02-05
Speaker: Dr. Som S. Bandyopadhyay
Venue: Room No. 469

Abstract

Suppose a composite quantum system is known to be in one of many states, not necessarily orthogonal, such that its parts are distributed among spatially separated observers. The goal is to learn about the state of the system using only local quantum operations and classical communication between the parties (LOCC). This problem, known as local state discrimination, is of considerable interest, as in many instances the information obtainable by LOCC is strictly less than that achieved with global measurements even when the states are mutually orthogonal. Thus the problem of local state discrimination serves to explore fundamental questions related to local access of global information and the relationship between entanglement and local distinguishability. In this talk I will present a self contained review of local state discrimination along with some recent results.

SUSY Dark Matter in Universal and Nonuniversal Gaugino Mass Models

Date: 2015-01-22
Speaker: Prof. D.P. Roy
Venue: Room No. 469

Abstract

Comments on Flavour mix, energies and fluxes of high energy astrophysical neutrino events seen at ICECUBE

Date: 2015-01-20
Speaker: Prof. Sandip Pakvasa
Venue: Room No. 469

Abstract

Leggett-Garg Inequalities and Device-Independent Randomness

Date: 2015-01-19
Speaker: Dr. Sujit K. Choudhary
Venue: Room No. 469

Abstract

Leggett-Garg inequalities (LGI) are constrains on certain combinations of temporal correlations obtained by measuring one and the same system at two different instants of time. The usual derivations of LGI assume macroscopic realism per se and non-invasive measurability. We derive these inequalities under a different set of assumptions, namely the assumptions of predictability and no signalling in time (NSIT). As a novel implication of this derivation, we find application of LGI in randomness generation. It turns out that randomness can be generated from temporal correlations, even without knowing the details of the experimental devices, provided the observed correlations violate LGI but satisfy NSIT.

Universality in the lepton sector

Date: 2015-01-16
Speaker: Prof. N. G. Deshpande
Venue: Room No. 469

Abstract

Testing New Physics Effects in B -> K^* l^+ l^-

Date: 2015-01-13
Speaker: Dr. Rahul Sinha
Venue: Room No. 469

Abstract

We show how the most general parametric form of the standard model amplitude for B -> K* l^+ l^- can take into account comprehensively all contributions within the standard model. This parametric form of the amplitude gives a new relation that does not rely on any approximations, however, innocuous. The violation of this relation provides a smoking gun signal of new physics. We use 1 fb^{-1} LHCb data to show that a robust signal of new physics is already being seen.

2014

High Scale Mixing Unification for Dirac Neutrinos

Date: 2014-12-23
Speaker: Dr. Gauhar Abbas
Venue: Room No. 469

Abstract

Starting with high scale mixing unification hypothesis, we investigate the renormalization group evolution of mixing parameters and masses for Dirac type neutrinos. Following this hypothesis, the PMNS mixing angles and phase are taken to be identical to the CKM ones at a unifying high scale. Then, they are evolved to a low scale using renormalization-group equations. The renormalization group evolution "naturally" results in a non-zero and small value of leptonic mixing angle $\theta_{13}$. One of the important predictions of this work is that the mixing angle $\theta_{23}$ is non-maximal and lies only in the second octant. We also derive constraints on the allowed parameter range for the SUSY breaking and unification scales, for which this hypothesis works. The results are novel and can be tested by present and future experiments.

Dynamical tunneling versus quantum coherent control

Date: 2014-12-22
Speaker: Prof. Srihari Keshavamurthy
Venue: Room No. 469

Abstract

Quantum coherent control is an area of active research. However, recently, studies are starting to determine the extent of quantumness needed for exerting control using external fields. At the same time, we now have a fairly detailed understanding of the process of dynamical tunneling and its mechanisms from a phase space perspective. In this talk I will present some of our recent results that establish the importance of dynamical tunneling for the coherent control scenario. Interestingly, resonance and chaos assisted tunneling can thwart simple but elegant coherent control approaches.

Elasto plastic response of reversibly crosslinked biopolymer bundles

Date: 2014-12-11
Speaker: Dr. Poulomi Sadhukhan
Venue: Room No. 469

Abstract

We study the response of crosslinked F-actin bundles to driving forces through a simple analytical model. Two failure modes under load can be defined. Brittle failure is observed when crosslinks suddenly and collectively unbind, leading to catastrophic loss of bundle integrity. During ductile failure, on the other hand, bundle integrity is maintained, however at the cost of crosslink reorganization and defect formation. We present phase diagrams for the onset of failure, highlighting the importance of the crosslink stiffness. We evidence how the introduction of defects can lead to complex elasto-plastic relaxation processes, once the force is switched off. Depending on, both, the time-scale for defect motion as well as the crosslink stiffness, bundles can remain in a quasi-permanent plastically deformed state for a very long time.

Payloads developed by SAC for Mars Orbiter Mission (MOM)

Date: 2014-11-27
Speaker: Moumita Dutta
Venue: Room No. 469

Abstract

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Interplay between Mutual Information and Success Probability: A Deeper Look into the Security of BB84

Date: 2014-11-21
Speaker: Goutam Paul
Venue: Room No. 469

Abstract

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Hilbert Space Theory of Classical Electrodynamics

Date: 2014-11-19
Speaker: Prof. Partha Ghose
Venue: Room No. 469

Abstract

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Vector perturbations in ELKO cosmology

Date: 2014-10-16
Speaker: Dr. Abhishek Basak
Venue: Room No. 469

Abstract

In this work we have analysed the first order vector perturbations in the context of inflationary model driven by non-standard spinor also known as ELKO. Unlike the standard scalar field driven inflation, the $\eta-i$ component of the first-order perturbed energy-momentum tensor of the ELKOS is non-zero indicating the plausibility of the generation of the pure vector part of the metric perturbation ($B_{i}$). The same component of the perturbed Einstein equation gives us the evolution equation of $B_{i}$. The evolution equation is solved under a condition on the background field which leads to super-inflation. Nearly time invariant and scale invariant solution for $B_{i}$ in super-horizon scale has been achieved.

Some Conceptual Issues in Finite Density QCD

Date: 2014-10-14
Speaker: Professor Rajiv Gavai
Venue: Room No. 469

Abstract

While a mature subject by itself, finite density quantum chromo dynamics (QCD), and indeed any finite density field theory, turns out to have some hidden issues which affect the modern lattice computations of interesting physical quantities. We point out what they are, and propose ways to handle them.

Higher spin particles: Past, Present and Future

Date: 2014-09-04
Speaker: Prof. M. Sivakumar
Venue: Room No. 469

Abstract

In this talk I survey the evolution of the study of higher spin particles since the days of quantum mechanics, and end with recent developments including Vasiliev's higher spin theory and point out some open problems in this subject. In the process a recent work of mine on higher spin couplings will be discussed.

Looking for Minimal Linear Seesaw Model at the Large Hadron Collider

Date: 2014-08-22
Speaker: Gulab Bhambaniy
Venue: Room No. 469

Abstract

In this talk I will discuss the Minimal Linear Seesaw Model(MLSM) in which two fermion singlets with opposite lepton numbers are added to the Standard Model (SM). The smallness of neutrino mass is explained through the small lepton number violating (LNV) Yukawa coupling. This allows to have both, TeV scale new physics as well as sizable light-heavy mixing, which are needed to have significant phenomenology of the model at LHC. The model is fully reconstructable in terms of neutrino oscillation parameters apart from the overall coupling. This coupling can be constrained from vacuum meta-stability and lepton flavor violating (LFV) process. The phenomenology of heavy neutrinos in this model at 14 TeV LHC will be discussed. The heavy neutrinos can be produced at LHC via S-channel and vector boson fusion (VBF) type of diagrams. The decay of heavy neutrinos lead to trilepton with missing transverse energy signal and VBF type signal which is characterized by two extra forward tagged jets. The significance of the signals will be discussed.

The power law Starobinsky model

Date: 2014-08-21
Speaker: Girish Chakravarty
Venue: Room No. 469

Abstract

In this talk I shall briefly discuss about the Starobinsky Model of Inflation and how we arrived at power-law form of the Starobinsky model from generalized curvature coupled models to tackle some of the issues in Starobinsky model. I shall also show that the most general Higgs-inflation models are equivalent to power-law correction to Einstein gravity and shall briefly try to discuss how these models are motivated by supergravity with the appropriate choice of the Kahler potential and superpotential.

Non-interferometric measurement of Pancharatnam phase

Date: 2014-08-13
Speaker: A. Aadhi
Venue: Room No. 469

Abstract

Pancharatnam phase is so called geometrical phase in optics associated with the polarized light. When a polarized light evolves on the Poincare sphere, its initial and final state acquire a phase difference, even though it comes back to its initial state, which is purely a geometrical consequence of the evolution of the state on the Poincare sphere. Pancharatnam found that for the cyclic evolution the phase difference will be half of the solid angle subtended by the closed path during the evolution. In general interference between the initial and final state is used to measure the Pancharatnam phase. In this talk I will discus about non-interferometric way of measuring the Pancharatnam phase. Further it can be extended to measure non-cyclic evolution of the initial state.

Quantum Scattering

Date: 2014-08-11
Speaker: Ananya Ghatak
Venue: Room No. 469

Abstract

Fluctuations in Relativistic Causal Hydrodynamics

Date: 2014-08-11
Speaker: Avdhesh Kumar
Venue: Room No. 469

Abstract

Hydrodynamic fluctuations arise due to finite particle number fluctuations in a given fluid cell. Intensity of these fluctuations is determined by equal time correlation functions which represents the correlation between the value of a given quantity to one space-time point to another. The dynamical properties of these fluctuations can be studied by time dependent correlation functions. In this seminar I shall discuss how the general theory of quasi stationary fluctuation can be used to calculate the hydrodynamic fluctuations in several relativistic causal hydrodynamics and Navier-Stokes hydrodynamics (acausal). We shall also discuss the time dependent nature of the hydrodynamic fluctuations for case of different relativistic hydrodynamics using one dimensional boost invariant (Bjorken) flow.

Generalized Higgs Inflation Model

Date: 2014-08-08
Speaker: Girish Kumar Chakravarty
Venue: Room No. 469

Abstract

In this talk I shall briefly discuss about scalar-curvature coupled Higgs-inflation model \xi\phi^2 R and the problems in this model in establishing Higgs as the Inflaton which drives the inflation and how could we overcome these by generalizing such a model to \xi\phi^a R^b. We shall also discuss about the equivalence of the Jordan and Einstein frames using our obtained results.

Unifying inflation with dark energy a la quintessential inflation

Date: 2014-08-04
Speaker: Prof. M. Sami
Venue: Room No. 469

Abstract

Simple models for structure, folding, and aggregation of proteins

Date: 2014-07-30
Speaker: Prof. Chin-Kun Hu,
Venue: Room No. 469

Abstract

The objective of statistical physics is to understand macroscopic behavior of a many-body system from the interactions of the constituents of that system. In the development of science, simple models have often been used to describe complex systems consisting of many components, e.g. the critical behavior of gas-liquid systems can be well described by the three dimensional Ising model and the Lennard-Jones system. In this talk, I briefly review some results from simple models for structures, folding, and aggregation of proteins. The last problem is related to neurodegenerative diseases. It is pointed out that in many cases, protein aggregation does not result from protein mis-folding. A potential drug from Chinese herb is found for Alzheimer's disease.

An ordered anarchy from a 5D SO(10)

Date: 2014-07-28
Speaker: Dr. Ketan Patel
Venue: Room No. 469

Abstract

The anarchical (structureless) Yukawa approach to understand the fermion masses and mixing angles will be described in a unified theory. Different hierarchies among the quarks and leptons result from the different localization of their 5-dimensional wave-function profiles which arise due to SO(10) breaking in the extra-dimension. Taking suitable scalar sector it is shown that the observed patterns of fermion masses and mixing angles can be well understood in terms of finite number of random structureless Yukawa couplings of order unity. Various aspects of the model construction and phenomenological results will be discussed.

Non-linear Nyquist theorem: A conjecture

Date: 2014-07-24
Speaker: Navinder Singh
Venue: Room No. 469

Abstract

We conjecture "a non-linear Nyquist theorem" for the first time. Our conjecture is based upon tests of the conjectured relation in specific systems in the thermodynamical limit. Nyquist theorem (that relates fluctuations with admittance) is a cornerstone in non-equilibrium statistical mechanics and is an example of the general class of relations called the fluctuation-dissipation theorem. In linear systems it is proved in its generality in a beautiful piece of work by Callen and Welton (in 1950s) . It states that r.m.s. value of fluctuations (in equilibrium) is proportional to the integral of linear admittance (non-equilibrium). We conjecture--with an explicit quantum mechanical calculation of non-linear admittance and fluctuations--that higher moments of the fluctuations bear a similar relation to {\it non-linear} admittance. Thus one can in principle compute non-linear admittance from the character of fluctuations--a relation that should have great practical applicability, for example, for electronic devices that operate under non-linear response.

Instabilities in Anisotropic Chiral Plasmas

Date: 2014-07-21
Speaker: Avdhesh Kumar
Venue: Room No. 469

Abstract

Kinetic theory can be applied to understand variety of many body problems arising in various branches of physics. This, however leaves out an important class of phenomena requiring triangle anomaly. Recently Son and Yamamoto have developed a modified kinetic theory that incorporate triangle anomalies and the chiral magnetic effect (CME) by taking into account Berry phase. They show that modified kinetic theory gives the identical results for the parity odd correlation function as computed from the perturbation theory in the next to leading order hard dense loop approximation. Using this modified kinetic theory in presence of the chiral imbalance the collective modes in the quasi-static limit were analyzed and found to be unstable. However in many realistic situations in condensed matter physics and in plasma physics it is important to consider equilibrium distribution function to be anisotropic in the momentum space. In this seminar I shall discuss modified kinetic theory to consider anisotropic chiral plasma and how even a small anisotropy can modify the chiral imbalance instability. I shall also discuss when a stream of charged particle travel in a thermally equilibrated isotropic chiral plasma may lead to a instability.

Equation-of-motion coupled-cluster method and its application to probe variation in the fine structure constant

Date: 2014-07-17
Speaker: Dillip Nandy
Venue: Room No. 469

Abstract

To answer the speculated concept of possible temporal variation of the fine structure constant (alpha), precise observations of the absorption lines in astrophysics are vital. These observational results in combination with accurately calculated sensitivity coefficients for the variation of the fine structure constant in the atomic energy levels can put stringent constraint on the variation of alpha. In this talk, I shall highlight some evidences on the variation of alpha from the astrophysical observations and compare them with the results obtained from the atomic clock experiments. For further investigations, we propose consideration of new astrophysical interesting candidates with enhanced alpha variation effects to extract out these information more convincingly. We have developed a relativistic coupled-cluster method in the equation-of-motion framework to perform the corresponding calculations which will be briefly discussed.

Gauge dependence of the fermion mass: Part 2

Date: 2014-07-15
Speaker: Prof. Ashok Das
Venue: Room No. 469

Abstract

Gauge dependence of the fermion mass: Part 1

Date: 2014-07-14
Speaker: Prof. Ashok Das
Venue: Room No. 469

Abstract

Fluctuation and interaction induced instability of dark solitons in single and binary condensates

Date: 2014-07-03
Speaker: Arko Roy
Venue: Room No. 469

Abstract

In this talk, we shall discuss about the stability of dark soliton in single and two-species Bose-Einstein condensates. We will show that the presence of soliton in a single-species condensate enhances the quantum depletion of the ground state which is sufficient enough to induce dynamical instability of the solitons in the condensate. On the other hand, for two-species condensates, in addition to the third Goldstone mode that emerges at higher interspecies interaction, due to the presence of the soliton in one of the components, a fourth Goldstone mode also arises. We use Hartree-Fock-Bogoliubov theory with Popov approximation to examine the mode evolution and demonstrate for specific values of interspecies interaction, when the anomalous mode collides with a higher energy mode it renders the solitonic state oscillatory unstable.

Status of 8-fold degeneracy after theta_13 discovery

Date: 2014-06-30
Speaker: Newton Nath
Venue: Room No. 469

Abstract

Standard 3-flavor neutrino oscillations depend on 6-oscillation parameters, namely 3-mixing angles(theta_13, theta_12, theta_23 ), 2-mass squared differences (Delta_m^2_21, Delta_m^2_31) and 1 CP - phase (delta_cp). In 1990s neutrino oscillations phenomenon were confirmed by different neutrino experiments like SK, SNO indicating that neutrinos do possess non-zero tiny mass. Today neutrino physics has reached an era of precision measurement. In this talk, I will discuss different parameter degeneracies present in the neutrino oscillation probability, collectively called 8-fold degeneracy. Muon neutrino survival probability (P_mu_mu) is sensitive to sin^2(2 theta_23) and sin^2(Delta_m^2_31 L/4E) this leads to two degeneracies, whether theta_23 is < 45^0 or > 45^0 and Delta_m^2_31>0 or <o. 8-fold degeneracy is due to (theta_13, delta_cp) , (hierarchy, delta_cp) and the octant degeneracy of theta_23. Reactor experiments like Double CHOOZ, Daya Bay, RENO have determined non-zero value of theta_13 upto 10 sigma level and the current global best fit value of theta_13 is around 8.8^0. Such a large mixing angle resolves the (theta_13, delta_cp) degeneracy. In this talk I will discuss how Long Baseline Experiments can help to resolve those degeneracies, especially in the context of large theta_13.

Evidence for leptonic CP phase from NOVA, T2K and ICAL

Date: 2014-06-26
Speaker: Monojit Ghosh
Venue: Room No. 469

Abstract

The phenomenon of neutrino oscillation is now well understood from the solar, atmospheric, reactor and accelerator neutrino experiments. This oscillation is characterized by a unitary PMNS matrix which is parametrized by three mixing angles and one phase known as the leptonic CP phase. Though there are already significant amount of information about the three mixing angles but the CP phase is still unknown. In my talk I will describe the synergy between the long-baseline (LBL) experiment NOVA, T2K and the atmospheric neutrino experiment ICAL@INO for obtaining the first hint of CP violation in the lepton sector.

Impact of perturbative QCD corrections on neutrinoless double beta decay

Date: 2014-06-19
Speaker: Namit Mahajan
Venue: Room No. 469

Abstract

I'll discuss perturbative QCD corrections and evolution under renormalization group for neutrinoless double beta decay, both for the short and long range parts.

Infrared properties of cuprates in the pseudogap state: A study of Mitrovic-Fiorucci and Sharapov- Carbotte scattering rates

Date: 2014-06-17
Speaker: Pankaj Bhalla
Venue: Room No. 469

Abstract

The frequency dependent scattering rate of generalized Drude model contains important physics on the electronic structure and on scattering mechanism. In this talk, we will discuss the frequency dependent scattering rate of cuprates (Mitrovic-Fiorucci/ Sharapov-Carbotte scattering rate) in the pseudogap phase using the non-constant energy dependent Yang-Rice-Zhang (YRZ) density of states. We will see the problems observed with traditional approach in the behavior of scattering rate and how our approach has sorted these issues. We will also discuss the experimental results of behavior of scattering rate and qualitative agreement of our results with them.

Left-right symmetry and the charged Higgs bosons at the LHC.

Date: 2014-06-12
Speaker: Gulab Bhambhaniya
Venue: Room No. 469

Abstract

Left-right symmetric models explain spontaneous violation of parity, which is ad-hoc in the Standard Model (SM). Along with this, LR symmetric models also provide light neutrino masses naturally. In this talk, we consider Minimal Manifest Left-right symmetric model (MLRSM) at TeV scale. We will focus on the charged Higgs boson sector of the model, in the context of LHC discovery search for beyond SM physics. Effects of charged scalars at colliders depend on their masses. Smaller the masses, larger effects are expected. But then the question is how small their masses can be, keeping the parity breaking scale large? Using the experimentally measured mass of the SM-like Higgs boson, experimental bounds on parity breaking scale and constraints due to the flavor changing neutral current (FCNC) effect, we analyzed the spectra of the charged scalars. The production of charged Higgs bosons and decay of these lead to multilepton signals at the LHC. Background and signals are analyzed with suitable kinematic cuts. We provide some benchmark points where simulations are done to make a realistic estimation of the signal events over the SM backgrounds. We will also discuss the impact of the charged scalars in the Higgs to di-photon decay rate .

Universal Extra Dimension with Boundary Localised Terms

Date: 2014-06-11
Speaker: Ujjal Kumar Dey
Venue: Room No. 469

Abstract

In this talk I'll briefly describe the universal extra dimensional (UED) model in the presence of boundary localised terms (BLT). In UED, conserved discrete symmetry, KK parity, leads to a stable particle in the spectrum and that can be a good dark matter candidate. The mass spectrum as well as the couplings of the model depends on these BLTs. I'll be discussing the novel features that arise on the plain UED after the inclusion of these BLTs. Constraints coming from recent collider and dark matter observations will also be discussed.

Copositivity and boundedness of the scalar potential

Date: 2014-06-05
Speaker: Tanmoy Mondal
Venue: Room No. 469

Abstract

There are experimental evidences that conclude that SM cannot be a complete theory of nature. Thus one needs to look for BSM physics. The BSM scenarios that include many scalar fields contain scalar potential with large number of quartic couplings. Due to the complicated structures of such scalar potentials it is indeed difficult to adjudge the stability of the vacuum. Thus one needs to formulate a proper prescription to compute the vacuum stability criteria. In this talk i will discuss the idea of copositive matrices to deduce the conditions that guarantee the boundedness of the scalar potential. As this idea is based on the mathematical arguments it evades the ambiguities while finding the stability criteria in the earlier used methods. It is also interesting to note that the copositive criteria allows us to find the stability conditions with larger parameter space.

Signature of Gibbons-Hawking temperature in the BICEP2 measurement of gravitational waves

Date: 2014-05-12
Speaker: Akhilesh Nautiyal
Venue: Room No. 469

Abstract

BICEP2 has detected gravitational waves with large tensor to scalar ratio r=0.2, that is in tension with PLANCK's upper bound r<0.11 from temperature anisotropy. The tension can be resolved if the spectrum of gravitational waves is blue tilted. As the standard inflationary models can not generate blue tilted spectrum, this may be a consequence of Hawking radiation seen by static observer inside the de Sitter Horizon. In this talk, after briefly discussing CMB polarization, we will discuss the signature of Hawking radiation on B-modes and its implications for BICEP2 and PLANCK.

Hawking Radiation and BICEP2

Date: 2014-05-01
Speaker: Prof. Subhendra Mohanty
Venue: Room No. 469

Abstract

I will summarise the recent result of gravitational wave observation by BICEP2 and its implications for cosmology. I will also survey the notion of Hawking Radiation (HR) and give examples of HR in different physical settings. Finally I will argue that the BICEP2 observations may be seeing a signature of Hawking temperature of the de-Sitter space at the time of Inflation.

Muon anomalous magnetic moment and positron excess at AMS-02 in a gauged horizontal symmetric model

Date: 2014-04-29
Speaker: Gaurav Tomar
Venue: Room No. 469

Abstract

The measurement of muon anomalous magnetic moment shows the discrepancy between the experimental value and the standard model prediction. We studied an extension of the standard model with vector lepton doublets to explain this discrepancy. The neutral components of the 4th generation vector lepton doublets identified as dark matter and can explain the positron excess seen in the AMS-02 experiment. In this talk we will discuss this model in details.

Can the observed CP asymmetry in tau to K pi nu_{tau} be due to Non-Standard Tensor interactions

Date: 2014-04-28
Speaker: Dr. H. Zeen Devi
Venue: Room No. 469

Abstract

The BABAR collaboration has measured that the decay rate asymmetry in the tau decay modes tau to K Pi nu has an opposite sign compared to the SM prediction. In this talk we will try to discuss how such a sign difference can be explained if we assume the presence of some non-standard tensor interaction.

Class of Higgs-portal Dark Matter models in the light of gamma-ray excess from Galactic center

Date: 2014-04-24
Speaker: Dr. Tanushree Basak
Venue: Room No. 469

Abstract

Recently the studies of anomalous gamma-ray emission in the Fermi-bubbles have drawn a lot of attention as it points out that the excess of ~ 1-3 GeV gamma-ray in the low latitude is consistent with the emission expected from annihilating dark matter. The best-fit to the gamma-ray spectrum corresponds to dark matter candidate having mass in the range ~ 31-40 GeV annihilating into b-bbar pair with cross-section ~ (1.4 - 2.0) x 10^(-26) cm^3 s^(-1). In this talk, we will discuss a class of Higgs-portal dark matter models, in presence of scalar resonance, which are well-suited for explaining these phenomena. We will also comment on a few Higgs-portal models which are found to be incompatible with the recent analysis.

Effective model study of low lying scalar mesons and Chiral phase transition

Date: 2014-04-17
Speaker: Dr. Tamal K. Mukherjee
Venue: Room No. 469

Abstract

In the framework of linear sigma model we study the effect of mixing between effective quarkonium and tetraquark as well as scalar glueball fields on the composition of low lying scalar meson (with mass below 2 GeV) and its implication to the chiral phase transition. Based on our study we will comment on what may be the mass of the lowest possible scalar and pseudoscalar glueball states. We will also discuss on what may be the nature of the sigma or f0(600) meson. With respect to the chiral phase transition we find the physical mass spectrum of mesons put a tight constraint on the parameter set of our model. We find a sufficiently strong cubic self interaction of the tetraquark field can drive the chiral phase transition to first order even at zero quark chemical potential. Weak or absence of the cubic self interaction term of the tetraquark field make the chiral pahse transition crossover at vanishing density.

Numerical Simulation of MHD Waves in the Solar Atmosphere

Date: 2014-04-07
Speaker: Prof. Robert von Fay
Venue: Room No. 469

Abstract

Photospheric motions, such as granular buffeting or vortices at the foot-point of magnetic flux tubes, could excite MHD waves, which propagate upwards though the solar atmosphere towards corona. In this talk I will show the results of 3D numerical simulation of generation and propagation of slow/fast magnetoacoustic and torsional Alfven modes in the localised waveguides and determine the energy flux they carry along the magnetic field lines. Also, the new analytical approach in construction of a system of multiple magnetic flux tubes, for example, pair of open tubes and complex mixed open tube configurations with curvature and asymmetry, will be discussed. This method provides an opportunity to build a range of analytical models of magnetic field configurations that will most realistically capturing magnetic structures of the lower solar atmosphere. About the speaker: Prof. Robert von Fay-Siebenburgen (Robertus) is the Director of Research at the School of Mathematics and Statistics at the University of Sheffield, UK. Prof. Robertus? group has a very high international reputation in the field of theoretical solar physics with particular expertise in the heating processes that generate and sustain the observed high temperature of the solar atmosphere by using both numerical and exact analytical methods and through observational studies using joint ground-based and satellite missions.

Search for new physics in the multijet and missing transverse momentum at CMS

Date: 2014-04-03
Speaker: Dr. Seema Sharma (CMS Collaboration)
Venue: Room No. 469

Abstract

An inclusive search for new physics is performed in multijet events with large missing transverse momentum produced in proton-proton collisions at sqrt(s)=8 TeV using a data sample corresponding to an integrated luminosity of 19.5 inverse femtobarns collected with the CMS detector at the LHC. The contribution of standard model processes is estimated using data driven techniques. The observed numbers of events in various search regions are consistent with expected backgrounds. Exclusion limits are presented for several simplified supersymmetric models of squark or gluino pair production. Discussion on SUSY search in multijets+MET final state (hep-ex 1402.4770), and a brief summary of current status of SUSY.

Non-chiral bosonization of fermions

Date: 2014-03-27
Speaker: Dr. Girish S. Setlur
Venue: Room No. 469

Abstract

In this talk, I describe the ongoing work in our group in recasting interacting fermion theories in a bosonic language with the aim of extracting asymptotically exact single particle Green functions. I describe the recent remarkable closed form expression of the Green function of a Luttinger liquid in presence of a single impurity (Kane Fisher problem). This talk will also introduce the concept of a non-local particle hole creation operator for both boson and fermion systems and point of their applications in computing the correlation functions.

U(1)_{B-L} extra-natural inflation

Date: 2014-03-21
Speaker: Dr. Kazuyuki Furuuchi
Venue: Room No. 469

Abstract

Recently there has been an increasing support for the hypothesis that our universe once experienced an extraordinary expansion called cosmic inflation at very early time. If the inflaton, whose potential caused the inflation, does not couple to particles which can be probed by current or near future experiments, it will be challenging to uncover its microscopic identity. However inflationary models based on well-motivated particle physics theories can be constructed, with the hope that one such model was indeed realized and we can test inflation also from particle physics experiments. In this talk I will present one example of single-field slow-roll inflation model which is closely connected to particle physics beyond the Standard Model. I will also discuss general theoretical issues in inflation.

Understanding Holography

Date: 2014-03-18
Speaker: Dr. Arjun Bagchi
Venue: Room No. 469

Abstract

The formulation of a quantum theory of gravity remains one of the principle challenges of theoretical physics today. The holographic principle is a unique route to address this problem. It relates a theory of gravity to a theory without gravity in one lower dimension thereby paving the way for "understanding gravity without gravity". In my talk, I present an introduction to this intriguing principle. The studies of the holographic principle has been mainly confined to Anti de Sitter spacetimes though the celebrated AdS/CFT correspondence. After mentioning this briefly, I go on to my own work which describes how one should formulate holography for the more physically relevant flat spacetimes. Our discussions would be principally based on symmetries. We will formulate flat holography as a limit of usual AdS/CFT and derive some very surprising and interesting results for 3d flat spacetimes.

Spin Current Driven Magnetization Dynamics and Applications in Spin Valve Pillars

Date: 2014-03-13
Speaker: C. Sanid
Venue: Room No. 469

Abstract

Spintronics is a contemporary area of technology which, in addition to the electric charge, makes use of the electron spin in designing novel, energy efficient and non-volatile memory devices and much more. In this talk the preliminary science and technology aspects needed to understand the developments in this emerging research area are introduced followed by a detailed presentation of two problems we have investigated - magneto logic gates and tunable spin torque nano oscillators.

Status report of the laser cooled Fr EDM experiment at CYRIC

Date: 2014-02-27
Speaker: Dr. Kenichi Harada
Venue: Room No. 469

Abstract

A permanent electric dipole moment (EDM) of the elementary particles has been drawing attention as a probe for the new physics beyond the standard model (SM) in the recent decades. We are constructing Fr beam line for the electron EDM (e-EDM) measurement at Cyclotron and Radioisotope center (CYRIC), Tohoku University. Francium (Fr) being the heaviest alkali atom has a large enhancement factor of about 900 for e-EDM. Moreover, laser cooling and trapping technique dramatically elongates the interaction time with an external electric field by two or three orders of magnitude, when compared to the conventional atomic beam experiments. I shall report the current status of the development of the Fr beam line and Magneto optical trap systems for the e-EDM search.

Aspects of Quantum criticality in ferroelectrics

Date: 2014-01-31
Speaker: Dr. Nabyendu Das
Venue: Room No. 469

Abstract

Some insulating dielectric materials, namely quantum paraelectrics are found to be near a quantum phase transition. Examples include SrTiO3, KTaO3 etc. Using an effective theory, which includes transverse optic phonons near zone centre as the most relevant degrees of freedom, a self consistent approach is proposed to explain the low temperature dielectric behavior of these materials. Using finite temperature scaling near a quantum critical point, 1/T^2 behavior of the paraelectric susceptibility is predicted. The theory is extended to describe other systems where quantum paraelectric fluctuations are coupled to anti-ferromagnetic fluctuations and quenched disorder.

Perturbation series and Landau pole of effective coupling constant in quantum electrodynamics

Date: 2014-01-30
Speaker: Prof. M. Azam
Venue: Room No. 469

Abstract

Matter Under Extreme Conditions

Date: 2014-01-23
Speaker: Dr. Brijesh K Srivastava
Venue: Room NO. 469

Abstract

Scientists have found that everything in the Universe is made up from a small number of basic building blocks called elementary particles, governed by a few fundamental forces. Some of these particles are stable and form the normal matter, the others live for fractions of a second and then decay to the stable ones. These particles can be created only at very high temperatures and densities in the laboratory. Therefore, studying particle collisions is like "looking back in time", recreating the environment present at the origin of our Universe. The talk will focus on the Equation of State of the Quark Gluon Plasma (QGP) created in the relativistic heavy ion collisions both at RHIC and LHC energies.

On the Origin of Neutrino Mass and Lepton Number Violating Searches

Date: 2014-01-20
Speaker: Dr. Manimala Mitra
Venue: Room No. 469

Abstract

Proof of neutrino masses and mixing from a series of outstanding experimental efforts have opened a window to physics beyond the standard model of particle physics. There must be some underlying theory which explains the tiny electron volt neutrino masses. It is well known that seesaw mechanism has its success in explaining the smallness of neutrino mass. In this talk I will discuss about the origin of neutrino masses and the different rich phenomenological aspects, that the underlying theories offer. The Majorana nature of the light neutrinos can be probed through the observation of lepton number violating processes. I will discuss about the different lepton number violating searches both at non-collider and collider experiments, emphasizing mostly on neutrinoless double beta decay. Apart from the well-known light neutrino contribution, lepton number violating states from a beyond standard model theory can also give large contribution in this process. I will emphasize on the sterile neutrino contribution in neutrinoless double beta decay and the interesting correlation with the lepton number violating searches at collider.

Searching for neutral Higgs bosons in non-standard channels

Date: 2014-01-09
Speaker: Dr. Arjun Menon
Venue: Room no. 469

Abstract

In a variety of well motivated models, such as two Higgs Doublet Models (2HDMs) and supersymmetric extensions of the Standard Model (SSM), there are additional neutral Higgs bosons. The tau-tau channel is the preferred mode for discovering such scalars at the LHC. However many of these models can have a suppressed tau-tau coupling and hence alternative discovery modes are required. In this talk, I will discuss two possible modes for searching for such neutral scalars. I will discuss the prospects of observing such scalars in the 3b and H to Z A channels at the LHC and compare our projections to the present LHC limits.

Identifying dark matter interactions in monojet searches at the LHC

Date: 2014-01-01
Speaker: Dr. Vikram Rentala
Venue: Room No. 469

Abstract

We study the discrimination of quark-initiated jets from gluon-initiated jets in monojet searches for dark matter using the technique of averaged jet energy profiles. We demonstrate our results in the context of effective field theories of dark matter interactions with quarks and gluons, but our methods apply more generally to a wide class of models. Different effective theories of dark matter and the standard model backgrounds each have a characteristic quark/gluon fraction for the leading jet. When used in conjunction with the traditional cut-and-count monojet search, the jet energy profile can be used to set stronger bounds on contact interactions of dark matter. In the event of a discovery of a monojet excess at the 14 TeV LHC, contact interactions between dark matter with quarks or with gluons can be differentiated at the 95% confidence level. For a given rate at the LHC, signal predictions at direct detection experiments for different dark matter interactions can span five orders of magnitude. The ability to identify these interactions allows us to make a tighter connection between LHC searches and direct detection experiments.

2013

Why do mean-field theories fail near the critical point and how does Wilson's renormalization group method go beyond that

Date: 2013-12-31
Speaker: Navinder Singh

Abstract

Mean field theories are good qualitative descriptors of the phase transition behaviour. But all mean-field theories (including Landau's theory) fail at the critical point (the problem of large correlation length). The problems with large correlation length in quantum many-body systems are the hardest problems known in theoretical physics (both in condensed matter (like high Tc cuprates) and in particle physics (like QCD)). It was Ken Wilson's physical insights and his powerful mathematical skills that opened a way to the solution of such hard problems. With above in perspective, we will address the following questions: Why do all the mean-field theories fail near the critical point? How does Wilson's program go beyond all the mean-field theories? What are physical meanings of various kinds of fixed points? What is emergence and universality? And what is the origin of universality? (sequel of: Thermodynamical Phase transitions, the mean-field theories, and thevrenormalization (semi)group: A pedagogical introduction(*)) (*) This presentation is our tribute to Ken Wilson (the pioneer of the renormalization group) who expired few months ago.

Thermodynamical Phase transitions, mean-field theories, and the renormalization (semi)group: A pedagogical introduction(*)

Date: 2013-12-26
Speaker: Dr. Navinder Singh
Venue: Room No. 469

Abstract

Lev Landau (the famous Russian physicist) made fundamental contributions in a wide spectrum of physical problems. While analysing second order thermodynamical phase transitions, he introduced a very vital concept, the concept of an "order parameter". This not only amalgamated the previous fragmentary theoretical understanding of phase transitions (an arsenal of mean-field theories) but also it put forward the important theory of "spontaneous symmetry breaking". Today, order parameter concept is a paradigm both in condensed matter physics and in high energy physics, and Landau theory is a pinnacle of all mean-field theories. Mean field theories are good qualitative descriptors of the phase transition behaviour. But all mean-field theories (including Landau's theory) fail at the critical point (the problem of large correlation length). The problems with large correlation length in quantum many-body systems are the hardest problems known in theoretical physics (both in condensed matter and in particle physics). It was Ken Wilson's physical insights and his powerful mathematical skills that opened a way to the solution of such hard problems. This presentation will be a perspective on these issues. Starting with simple examples of phase transitions (like ice/water; diamond/graphite etc) we will address the following fundamental questions: Why does non-analyticity (sharp phase transitions) arise when thermodynamical functions (i.e., free energies etc) are good analytic functions? How does Landau's program unify all the previous mean-field theories? Why do all the mean-field theories fail near the critical point? How does Wilson's program go beyond all the mean-field theories? What are physical meanings of various kinds of fixed points? What is emergence and universality? Although the presentation will deal with mundane phenomena, we will also discuss the Anderson-Higgs mechanism and the origin of mass (the Higgs boson) which is a consequence of spontaneous symmetry breaking of "the vacuum" (by comparing that with a similar phenomenon in superconductors). (*) This presentation is our tribute to Ken Wilson (the pioneer of the renormalization group) who expired few months ago.

Dynamical generation of the Higgs potential and CW inflation

Date: 2013-12-09
Speaker: Professor Eung Jin
Venue: Room No. 469

Abstract

Assuming the full scalar potential vanishing at the vacuum instability scale, a successful radiative generation of the Higgs potential is achieved in the framework of a generalized B-L gauge symmetry with two free parameters, the B-L gauge coupling and the right-handed neutrino Yukawa coupling. The B-L gauge symmetry is broken spontaneously by the Coleman-Weinberg mechanism while the scale symmetry breakdown induces electroweak symmetry breaking through the radiative generation of appropriate scalar quartic couplings. Then, we revisit a small field Coleman-Weinberg inflation in this scheme. The observed amplitude of perturbations needs an extremely small quartic coupling of the inflaton which is claimed to be a signature of radiative origin. However, the spectral index obtained in a standard cosmological scenario turns out to be outside the 2 sigma region of the Planck data. When a non-standard cosmological framework which modifies the evolution of the Hubble parameter is invoked, the spectral index can be made consistent with Planck data within 1 sigma.

Quantum Phases of Ultracold Bosonic Atoms in a One Dimensional Optical Superlattice

Date: 2013-12-05
Speaker: Prof. B. P. Das
Venue: Room No. 469

Abstract

Ultracold atoms in optical lattices have provided important insights into a wide range of physical phenomena during the past decade. My talk will begin with the landmark observation of the superfluid to Mott insulator transition in ultracold bosonic atoms in optical lattices in 2002 and then focus on the different quantum phases of ultracold bosonic atoms in a periodic one dimensional optical superlattice. The theoretical approach used in obtaining these phases will be briefly discussed. The physical situations that lead to the emergence of the Mott insulator and the superfluid phases as well as Mott insulators induced by the superlattice will be explained. Results showing the coexistence of the superfluid phase with the superlattice induced Mott insulator will be presented.

Theoretical study of electric dipole moment of ^{129}Xe atom

Date: 2013-12-03
Speaker: Yashpal Singh
Venue: Room no. 469

Abstract

Joining the seven decade long search for the existence of permanent electric dipole moment (EDM) of fundamental particles, atoms and molecules, we carry out theoretical investigation of EDM in ^{129}Xe atom. The current limits of the CP violating coupling coefficients obtained from the atomic EDMs are several orders of magnitude higher than the standard model predicted values. They, indeed, have the potential to contribute for the amount of CP violation required for explaining the matter-antimatter asymmetry of the Universe. To date the best limit for a diamagnetic atomic EDM is obtained from ^{199}Hg atom but three experiments by the leading groups around the world have considered EDM measurements in ^{129}Xe atom to surpass the present limit owing to its larger spin relaxation time. To extract the information of CP violating electron-quark coupling coefficient, EDM of a quark or other QCD parameters from the Xe EDM measurement, accurate calculations of the enhancement factors due to P- and T- violating operators and nuclear Schiff moment are necessary. In this talk, I shall briefly discuss the P- and T- violating interactions and origin of Schiff moment that are of interest for the Xe EDM study and present their high precision calculations using relativistic atomic many-body methods.

Aspects of type IIB large volume D3/D7 mu-Split SUSY

Date: 2013-11-29
Speaker: Dr Mansi Dhuria
Venue: Room No.469

Abstract

A phenomenological model is presented which can be obtained as a local Swiss-Cheese Calabi-Yau string-theoretic compactification with a mobile D3 and fluxed stacks of wrapped D7-branes, and provides a natural realization of mu-Split SUSY with a high SUSY-breaking scale wherein the squarks, sleptons, gauginos,Higgsino and one Higgs are very heavy and with fine tuning, one is able to obtain a 125-GeV light Higgs. We discuss the role of the (a) heavy squarks and sleptons in (ai) obtaining long-lived gluinos (a natural consequence of split SUSY), (aii) in verifying that the NLSP decays into the gravitino LSP respects the BBN constraints with the lifetime of the LSP(gravitino) coming out to be of the order or larger than the age of the universe, and (b) the light Higgs in obtaining (bi) a gravitino relic abundance of around 0.1, and (bii) electronic EDM close to the experimental upperbounds.

Invisible decays of the lightest Higgs boson in supersymmetric models

Date: 2013-11-28
Speaker: Dr. Monalisa Patra
Venue: Room no. 469

Abstract

In various supersymmetric models the lightest Higgs scalar can decay invisibly consistent with the constraints on the 126 GeV state discovered at the CERN LHC. I will briefly state the status of the invisible decays in the light of recent LHC data on SUSY and Higgs. Â Then I will mainly focus on the implications of these observations for the neutralino sector Â in the minimal supersymmetric standard model (MSSM), as well its extension containing an additional chiral singlet Â superfield, the so-called next-to-minimal or nonminimal supersymmetric standard model~(NMSSM), with both universal as well as Â nonuniversal gaugino masses at the grand unified scale.

'Rogue' Ocean Optics: The story of Peregrine Solutions

Date: 2013-10-30
Speaker: Prof. Prashanta K. Panigrahi
Venue: Room No. 469

Abstract

Rogue waves are 'walls of water' in ocean, which appear from no-where and vanishes fast, leaving no trace behind'. These has been observed in optical fibers and are being harnessed for generating super continuum, an extremely broad band source of light. They are descibed by the well-known non-linear Schrodinger equation. We will illustrate their structure and means of controlling their transient excitations.

Perturbative expansion improved by renormalization-group summation and conformal mappings of the Borel plane for the QCD Adler function

Date: 2013-10-15
Speaker: Prof. B. Ananthanarayan
Venue: Room No. 469

Abstract

The extraction of the strong coupling constant in a reliable manner is one of the important challenges of elementary particle physics research. We will describe in detail some of our detailed theoretical investigations on this subject which employs a novel renormalization group summation scheme, which when applied to the hadronic decay of the tau produces excellent results. In this talk, we will discuss all the ingredients in a highly accessible manner, as many of the ingredients can be explained from an elementary standard point.

Astrophysically Interested Highly Charged Ions for Probing Temporal Variation of the Fine Structure Constant

Date: 2013-10-10
Speaker: Dillip Nandy
Venue: Room No. 469

Abstract

The possibility of temporal variation of the fine-structure constant α=e2/(ℏc) at the cosmological time scale is a subject of current interest involving particle, atomic and astro physics. Insights into this fascinating topic can be obtained from the spectral line analysis using a relativistic many-method in combination with their laboratory and/or astrophysical observations. In this seminar, I will briefly discussdifferent procedures for detecting any plausible variation of α in time and demonstrate large enhancement of this effect in the highly charged ions using a recently developed many-body method that could lead to astrophysical observation of the above subtlety in the remote past.

Extreme events and network failures

Date: 2013-08-29
Speaker: Vimal Kishore
Venue: Room No. 469

Abstract

Events like traffic jams, floods, and power blackouts are not uncommon. Inspired by such events, we study extreme events on complex networks. In this talk, we will discuss the random walk on network and associated extreme events taking place on networks. We will also propose a model to study network failures based on extreme events and discuss the nature of such failures

Experimental Signature of cosmological neutrino condensation

Date: 2013-08-23
Speaker: Prof. M. Azam
Venue: Room No. 469

Abstract

Superfluid condensation of cosmological background neutrinos has been proposed as an alternative mechanism for generation of neutrino mess. This condensation at a low enough temperature also gives rise to a late time cosmological Constant of small magnitude. We propose that a carefully prepared beta decay experiment in laboratory can be used to find observational signature of such a condensation.

Higgs(es) in Triplet extended supersymmetric standard model at LHC

Date: 2013-08-02
Speaker: Priyotosh Bandyopadhyay
Venue: Room No. 469

Abstract

We will discuss the recent Higgs discovery results both by CMS and ATLAS at the LHC. In this context we will see the status of supersymmetric scenarios. In minimal supersymmetric scenarios to have a ~125 GeV Higgs, one needs quantum correction from strong supersymmetric sector which demands either large suspersymmetric mass scale or large mass splitting between the contributing super-particles. We focus on the triplet extension of minimal supersymmetric scenario, where we can see that the electro-weak contribution coming from triplet is also important and comparable to the strong contributions. We discussthis in the context of the observed Higgs like particle around 125 GeV and also look into the status of other Higgs bosons in the model. Along with the Higgs result we also consider flavour constraint coming from rare B decay. Finally we discuss the phenomenology of this model at the LHC.

Quantum Statistics of Light from Optical Parametric Oscillator

Date: 2013-07-26
Speaker: Prof. Reeta Vyas
Venue: Room No. 469

Abstract

Optical parametric oscillators (OPOs) based on frequency down conversion are quantum mechanical sources of light with a definite threshold for self-sustained oscillations. They can be operated in degenerate or non-degenerate modes and the light generated by them exhibits nonclassical fluctuations. We obtain analytic expressions for probability distribution functions, which are valid though out the threshold region and study their fluctuations properties below, near, and above threshold. We discuss nonclassical effects in various measurable quantities such as the mean,variance, and skewness of the intensity, and quadrature squeezing, and compare with those for the single and two mode lasers

Hadronic origin TeV gamma rays and High Energy Cosmic Rays from AGN

Date: 2013-07-25
Speaker: Prof. Sarira Sahu
Venue: Room No. 469

Abstract

Centaurus A (Cen A) is the nearest radio-loud AGN and is detected from radio to very high-energy gamma rays. Its nuclear spectral energy distribution (SED) shows a double-peak feature, which is well explained by the leptonic synchrotron self-Compton model. This model however can not account for the observed high energy photons in the TeV range, which display a distinct component. Here, we show that TeV photons can be well interpreted as the neutral pion decay products from proton-gamma interactions of Fermi-accelerated high-energy protons in the jet with the seed photons around the second SED peak at 170 keV. Extrapolating the inferred proton spectrum to high energies, we find that this same model is consistent with the detection of two ultra-high-energy cosmic ray events detected by Pierre Auger Observatory from the direction of Cen A. We also estimate the GeV neutrino flux from the same process, and find that it is too faint to be detected by current high-energy neutrino detectors. In addition I shall also discuss about the flaring from Blazars using this hadronic model.

Studies of Reheating after inflation through f(φ)R gravity

Date: 2013-07-12
Speaker: Arun Kumar Pandey
Venue: Room No. 469

Abstract

Inflation is essential building block of the standard model of cosmology and has passed a number of stringent observational tests. Any inflation models must contain a mechanism by which the universe re-heats afterinflation. The reheating mechanism requires details knowledge of interactions between inflaton fields and their decay products. Since the physics behind inflation is beyond the standard model of elementary particles, the precise nature of inflaton fields is currently undetermined, and the coupling between inflaton and matter fields is often put by hand. It has found that, reheating can occure spontaneously without introducing any extra interaction between inflaton and the decay products, if inflaton is coupled nonminmally with gravity. So in this case, it is found that, inflaton field coupled with gravity nonminmally can give another channel for decay. So in this seminar, I will first discuss about reheating and then will present the reheating through a f (φ)R gravity

Analysis of the scalar potentials of "B-L" extended models

Date: 2013-07-11
Speaker: Tanmoy Mondal
Venue: Room No. 469

Abstract

The knowledge and informations related to the Standard Model (SM) Higgs mass are very crucial to understand the physics beyond it. SM-like Higgs boson, having mass in the range 123-127 GeV, squeezes the beyond standard model parameters. In recent LHC era many TeV scale neutrino mass models have earned much attention as they pose many interesting phenomenological aspects. We have considered "B-L" extended models which are theoretically well motivated and phenomenologically interesting and successfully explain neutrino mass generation. I will discuss the vacuum stability criteria for different models and how it can constrain the parameters of such models.

Relativistic heavy-ion collisions and causal viscous hydrodynamics

Date: 2013-07-10
Speaker: Manu George
Venue: Room No. 469

Abstract

Relativistic heavy ion collisions set a platform to study the properties of matter at very high temperature (T>200 MeV). The colour-deconfinement phase transition can occur at such a high temperature. This new phase of nuclear matter is called quark-gluon plasma(QGP),where quarks and gluons are no longer confined inside the hadronic volume, but move freely in a bigger volume occupied by the colliding nuclei. Relativistic hydrodynamic formalism is highly successful in describing space-time evolution of the particles produced in relativistic heavy ion collisions.One of the very important question to study in relativistic-heavy ion collision, is to accurately determine the viscosity of the strongly interacting matter. The relativistic Navier-Stokes equation is known to violates causality and gives unphysical behavior. Therefore one has to look for an alternate hydrodynamic description. One of the widely used such hydrodynamic description is due to Muller,Israel and Stewart. In this talk I will discuss about development of relativistic fluid dynamics up to second order.

Fermi-LAT signal of monochromatic gamma ray from B-L extended SM

Date: 2013-07-08
Speaker: Tanushree Basak
Venue: Room No. 469

Abstract

The recent observation of Fermi-LAT signal of monochromatic gamma ray has drawn much attention. This observation can be due to the resonant annihilation of the dark matter into two photon. We adopt a (B_L) extended SM which contains a singlet scalar and three right-handed neutrino. The vev of the singlet scalar breaks the U(1)B−L symmetry. This scalar is heavier than the SM ones -- having mass 260 GeV. We have imposed a Z2 symmetry in such way that the 3rd generation right-handed neutrino is qualified as the dark matter candidate. The mass of this right-handed neutrino is 130 GeV. We constrain the scalar mixing angle from relic density and desired cross-section ⟨σv⟩γγ for the Fermi-line. We have also checked that this mixing angle allows vacuum stability of this model up to 105 GeV. This might hint that the successful U(1)B−L extended model that can explain Fermi-LAT signal of monochromatic gamma ray line must be a part of larger symmetry group at some high scale.

Bulk viscosity of strongly interacting matter

Date: 2013-07-05
Speaker: Guruprasad Kadam
Venue: Room No. 469

Abstract

Quantum ChromoDynamics (QCD) describes the strong interaction physics at a fundamental level. While the Lagrangian of QCD is scale invariant, quantum effects break this symmetry. This is called scale anomaly. The violation of scale invariance manifests itself in the bulk viscosity of the strongly interracting matter; so its study becomes an important as well as interesting aspect of QCD and its phases. Low temperature thermodynamics of QCD can be described by hadron resonance gas model (HRG),an effective model where the elementary degrees of freedom are hadrons. In this talk I will discuss the calculation of the bulk viscosity at finite temperature and density using Kubo's formula in the light of HRG.

ϵ′/ϵ in Standard Model

Date: 2013-07-02
Speaker: Girish Kumar
Venue: Room No. 469

Abstract

CP violation is the violation of compound symmetry associated with charge conjugation (C) and parity (P) by the weak force. It has been nearly 50 years since the surprising discovery of violation of CP symmetry in hadronic decays of kaon decays was made yet it remains as a fascinating effect because of its elusiveness at both the experimental and theoretical levels. Complex parameters ϵ and ϵ′ parametrize the indirect and direct CP violation respectively in kaon decaying to two pion. In this talk, parametrization of two pion decay will be presented. After introducing the basic formalism of operator product expansion (OPE) in weak decays , which is a formal framework to derive low energy effective theory of weak interaction of quarks, we shall discuss the theoretical status of ϵ′/ϵ in Standard Model.

The last tango of a vortex-antivortex pair

Date: 2013-06-27
Speaker: Kuldeep Suthar
Venue: Room No. 469

Abstract

The investigation of vortices in superfluids is a fascinating and active line of research that, by now, has a history spanning over half a century. Starting from the first observations of quantized circulation in liquid helium in the 1950s, the field has undergone tremendous progress. Nowadays, Bose-Einstein condensates (BECs) of dilute atomic gas provide a powerful tool with which vortex research can be pushed into new regimes. We theoretically investigate the effect of a repulsive barrier on the dynamics of vortex dipole. In the presence of barrier, a delicate dance ensues, and the quantum whirlpools eventually annihilate each other followed by emitting a burst of acoustic waves. In this talk, I shall discuss the effect of curvature of the vortex line on the dynamics using matched asymptotic expansion in Frenet-Serret coordinates. Finally I shall discuss the effect of transverse anisotropy of the condensate on the annihilation event.

Phase coherence in finite temperature Bose-Einstein condensates

Date: 2013-06-20
Speaker: Dr. Sandeep Gautam
Venue: Room No. 469

Abstract

We study the Bose-Einstein condensates (BECs) at non-zero temperatures using stochastic Gross-Pitaevskii equation (SGPE). This is a Langevin equation which takes the form of non-linear Schrodinger equation with additional noise and damping terms. The use of the SGPE to study both the scalar and spinor BECs at finite temperatures will be discussed in the talk. I will discuss the effect of anharmonicity on the phase coherence of quasi one-dimensional condensates.

Two-photon fields: coherence, interference and entanglement

Date: 2013-06-19
Speaker: Dr. A. K. Jha
Venue: Room No. 469

Abstract

One of the most widely used processes for generating entangled two-photon fields is parametric down-conversion. It is a second-order nonlinear optical process in which a pump photon interacts with a nonlinear crystal and breaks up into two separate photons known as the signal photon and the idler photon. The constraints of energy and momentum conservation render the two photons entangled in several different variables including time and energy, position and momentum, and angular position and orbital angular momentum. In this talk, I will present our studies of the coherence and entanglement properties of the down-converted two-photon field and will also discuss some of the practical implications of these studies for quantum information science.

When 133Cs condensate meets 87Rb condensate at finite temperature

Date: 2013-06-13
Speaker: Arko Roy
Venue: Room No. 469

Abstract

In this talk, we shall discuss the effects of finite temperature on the ground state structures of binary condensates in a highly elongated cigar-shaped trap, quasi-1D system. For this the Gross-Pitaevskii (GP) equation, valid at zero temperature, is generalized to include the effects of the interaction of the condensate with the thermal cloud, which is present at finite temperatures. For our study we use the self consistent gapless Hartree-Fock-Bogoliubov-Popov formalism, which was developed tostudy single species condensates at finite temperatures. We generalise the method to binary condensates and use it to study the ground state geometry of phase-separated profiles of binary condensates. In the strongly phase-separated domain we find doubling of Goldstone modes.

Explaining Fermi-line and enhanced Higgs di-photon rate in the Triplet-Singlet extended MSSM

Date: 2013-06-06
Speaker: Tanushree Basak
Venue: Room No. 469

Abstract

We propose an economic extension of minimal supersymmetric standard model with a SU(2) singlet and Y = 0 triplet, which can explain (i) the 125 GeV Higgs boson without fine tuning, (ii) the 130 GeV gamma-ray line seen at Fermi-LAT, (as well as a second photon line at 114 GeV)(iii) an enhanced Higgs di-photon decay rate seen by ATLAS, while being consistent with dark matter relic density and recent XENON 100 exclusion limits on spin-independent direct detection cross-section. We obtain the required cross-section of 10−27cm3s−1 for the 130 GeV gamma-ray flux through the resonant annihilation of dark matter via pseudoscalar triplet Higgs of mass ~260 GeV. The dark matter is predominantly bino-higgsino which has large couplings with photons (through higgsino) and gives correct relic ensity (through bino). We get the enhanced Higgs diphoton decay rate, R ~ 1.224, dominantly contributed by the light chargino-loops, which can account for the reported excess seen in the h to gamma gamma channel by ATLAS.

A novel scheme for qudit teleportation

Date: 2013-05-23
Speaker: Chithrabhanu P
Venue: Room No. 469

Abstract

Quantum teleportation is the process in which, the quantum state of a particle is transferred to another without direct interaction. Efficient quantum teleportation of multi dimensional quantum bit (qudit) is one of the prime requirement in quantum circuits. We investigate the possibility of a new entanglemed state for 100% qudit teleportation. In the talk I will discuss the basic teleportation protocol, its experimental realization, hyper entanglement , possibility of a new entangled state and its use in qudit teleportation.

Annihilation of vortex dipoles in Bose-Einstein Condensate

Date: 2013-05-16
Speaker: Shashi Prabhakar
Venue: Room No. 469

Abstract

One of the recent developments in experiments on atomic Bose-Einstein Condensate (BEC) is the creation of vortices and study of their dynamics. We have theoretically explored the annihilation of vortex dipoles, generated by the movement of obstacle through an oblate BEC. We have also examined the energetics of the annihilation events. We have observed that the gray soliton, which results from the vortex dipole annihilation, is lower in energy than the vortex dipole. We have also observed the annihilation events numerically and found that the annihilation occurs only when the vortex dipole overtakes the obstacle and comes closer than the coherence length. Furthermore, we have found that the noise reduces the probability of annihilation events. This may explain the lack of annihilation events in experimental realizations. In this talk, we will discuss about observations obtained from the study on annihilation of vortex dipoles in BEC

Coherent pump-probe spectroscopy of atomic and molecular systems

Date: 2013-04-29
Speaker: Ms. Niharika Singh
Venue: Room No. 469

Abstract

Quantum coherence and interference provide an interesting outlook for designing strategies for the control of optical response of atomic/molecular medium. This theme is the main focus of the work presented in this talk. The specific issues addressed are electromagnetically induced transparency (EIT), amplification without inversion (AWI) and spontaneously generated coherence (SGC). Also examined are the issues related to the effect of permanent dipole moments on the coherent dynamics of molecular systems and realization of negative refractive index in coherently prepared atomic medium. These phenomena help to understand the subtle quantum effects in laser-atom interactions, they on the other hand provide useful platform for development of quantum technologies.

Spectroscopic Properties of atoms/ions in the presence of screened inter-electron interaction.

Date: 2013-04-25
Speaker: Dr. Madhulita Das
Venue: Room No. 469

Abstract

We have theoretically studied the atomic structure and properties of multi-electron system in both weak and strong plasma environment using Debye and Ion-Sphere model, respectively. The Many-body method adapted for the computation is the Relativistic Coupled Cluster method to include eﬀectively the relativistic and correlation effects in the calculations using Gaussian type orbital (GTO). In addition to nuclear screening effect, the plasma screening effect have been extended to electron-electron Coulomb interaction between the atomic electron of highly charged atomic/ionic systems embedded in plasma. The main focus is to analyze the inﬂuence of inter-electron screening effect on the spectroscopic properties of highly charged Lithium iso-electronic sequence with increasing plasma strength.

Vacuum polarization correction in many electron atoms with triples excitation in relativistic coupled-cluster theory

Date: 2013-04-18
Speaker: Siddhartha Chattopadhyay
Venue: Room No. 469

Abstract

In this talk We shall discuss about the importance of the vacuum polarization correction in the calculation of orbital energies in many electron atoms. The Uehling potential is the leading order term in the vacuum polarization. We incorporated the Uehling potential in the Dirac-Hartree-Fock self consistent field calculation of many electron atoms. We shall discuss how it affects the orbital energies and why it is important for highly charged ions. We will discuss some preliminary results of highly charged Barium ions. In the next part we will discuss about the triples excitation in the relativistic coupled-cluster (RCC) theory. Most of the RCC calculations are done with the singles and doubles excitations. Because of complicated angular momentum diagram and enormous computational cost there are very few calculations have been performed with the actual triples excitation. We will discuss the necessity of triples excitation in present era of high precision calculation. We will present some preliminary results of Lithium in the framework of RCCSDT theory.

Status of two popular models of supersymmetry with and without seesaw

Date: 2013-04-04
Speaker: Dr. Ketan Patel
Venue: Room No. 469

Abstract

The results of updated analysis will be presented for two highly-constrained models of supersymmetry -- the constrained minimal supersymmetric standard model (cMSSM) and the non-universal Higgs mass model (NUHM) -- in the light of the recent discovery of Higgs boson and updated results on the several flavour physics observables. It turns out that these models can still survive and predict a light stop with mass < 1.5 TeV. I will also report on the status of the extended versions of cMSSM and NUHM models which accommodate seesaw mechanisms. The recent measurement of the reactor angle and new MEG limit on μ → e γ provide powerful constraints on these class of models. The potential of the current and future experimental searches in constraining the supersymmetric parameter space will also be discussed.

Higgs-to-diphoton in type II seesaw

Date: 2013-03-28
Speaker: Dr. Pankaj Sharma
Venue: Room No. 469

Abstract

I will talk about Higgs-to-diphoton rate in type II seesaw model. We also discuss the constraints on the model parameter space coming from vacuum stability, perturbativity and electroweak precision tests. In the constrained parameter space, we study the modified Higgs-to-diphoton rate.

Mass measurement techniques for BSM particles in collider experiments

Date: 2013-03-22
Speaker: Abhay Kumar Swain
Venue: Room No. 469

Abstract

Most of the theories beyond the Standard Model(BSM) includes unstable heavy particles which can decay into a stable invisible particle. If LHC observes any BSM particles we must be able to determine their masses and other properties. In this talk I will discuss some of the mass measurement techniques which tell how to measure the masses of both stable as well as unstable particles in collider experiments.

Centenary of Bohr's Atom Model and its relevance to contemporary science

Date: 2013-03-14
Speaker: Prof. M. D. Sastry
Venue: Room No. 469

Abstract

-NA-

Quark and Gluon Angular Momenta Contributions to Nucleon Spin (χQCD Collaboration)

Date: 2013-03-07
Speaker: Dr. Mridupawan Deka
Venue: Room No. 469

Abstract

The nucleon spin structure has been a longstanding issue in hadronic physics,both experimentally and theoretically. From the polarized Deep Inelastic Scattering experiments and Lattice QCD calculations, it has been found that the contribution coming from the quark spin is rather small (~25%). Now, it is widely accepted that the rest of the nucleon spin should come from the gluon spin and the orbital angular momenta of quarks and gluons. In this talk, I will present a complete Lattice QCD calculation of the quark and glue angular momenta inside a proton. The calculation is carried out on a 16^3×24 quenched lattice using the standard Wilson action.

Neutino mass Hierarchy and Octant determination with T2K and NoVA

Date: 2013-02-22
Speaker: Professor S. Umashankar
Venue: Room No. 469

Abstract

I will discuss the resolution of two outstanding issues in neutrino physics -- mass hierarchy and octant of the 2-3 mixing angle in the upcoming long baseline experiments T2K and NOVA.

Spectral statistics of interacting trapped bosons

Date: 2013-02-21
Speaker: Prof. Barnali Chakrabarty
Venue: Room No. 469

Abstract

It is very much interesting to study the energy-level statistics of interacting trapped bosons which are spatially inhomogeneous. We study the zero-temperature many-bosons system interacting through thevan der Waals potential and confined in a 3D harmonic potential. The system is a kind of complex system where the two energy scales co-exist. One is the external trap and another is the interatomic interaction. In case of repulsive interaction the lower levels are correlated manifesting level-repulsion. For non-interacting bosons exact degeneracy exists and the energy-level statistics shows picket-fence type nature. But for a few bosonic system the small interaction acts like perturbation and consequently a large number of quasi-degenerate states occur showing Shnirelman peak in P(s) distribution. For large number of bosons the low-lying levels are of collective nature and strongly affected by the interatomic interaction whereas the high-lying levels show single particle excitations. The corresponding level fluctuation shows a transition from close to Wigner to Poisson with increase in energy levels implying that it does not obey the Bohigas universal conjecture. Thus interacting trapped bosons may be a generic example to show that 1/fα noise is ubiquitous in nature and α not only measures the chaoticity of the system but also measures the degree of integrability for complex systems.

Lepton masses and Flavour violation in Randall Sundrum Model

Date: 2013-02-07
Speaker: Abhisek Iyer
Venue: Room No. 469

Abstract

Lepton masses and mixing angles via localization of 5D fields in the bulkare revisited in the context of Randall-Sundrum models. The Higgs is assumed to be localized on the IR brane. Three cases for neutrino masses are considered: (a) The higher dimensional LH.LH operator (b) Dirac masses (c) Type I see-saw with bulk Majorana mass terms. Neutrino masses and mixing as well as charged lepton masses are fit in the first two cases using chi-square minimisation for the bulk mass parameters, while varying the O(1) Yukawa couplings between 0.1 and 4. Lepton flavour violation is studied for all the three cases. It is shown that large negative bulk mass parameters are required for the right handed fields to fit the data in the LH LH case. This case is characterized by a very large Kaluza-Klein (KK) spectrum and relatively weak flavour violating constraints at leading order. The zero modes for the charged singlets are composite in this case and their corresponding effective 4-D Yukawacouplings to the KK modes could be large. For the Dirac case, good fitscan be obtained for the bulk mass parameters, ci, lying between 0 and 1. However, most of the `best fit regions' are ruled out from flavour violating constraints. In the bulk Majorana terms case, we have solved the profile equations numerically. We give example points for inverted hierarchy and normal hierarchy of neutrino masses. Lepton flavor violating rates are large for these points. We then discuss various minimal flavor violation (MFV) schemes for Dirac and bulk Majorana cases. In the Dirac case with MFV hypothesis, it is possible to simultaneously fit leptonic masses and mixing angles and alleviate lepton flavor violating constraints for Kaluza-Klein modes with masses of around 3 TeV. Similar examples are also provided in the Majorana case.

Study of Sources in very High Energy Regime Using Ground Based Gamma-ray and Neutrino Telescopes

Date: 2013-02-06
Speaker: Dr. Debanjan Bose
Venue: Room No. 469

Abstract

In this presentation I will talk about sources like pulsars, AGN and GRBs in very high energy regime. At these energies we study non-themal Universe. From observations we know that relativistic effects are taking place inside these objects. These sources emit high energy gamma-rays and are also expected to emit neutrinos. I will explain detection principle of gamma-rays and neutrinoswith earth based detectors. I will also discuss some important observations for the above mentioned sources with ground based Cherenkov telescopes and IceCube neutrino observatory. Finally, I will briefly talk about neutrino point source analysis following Bayesian statistics.

Black hole membrane paradigm

Date: 2013-01-24
Speaker: Dr. Sudipta Sarkar
Venue: Room No. 469

Abstract

Black hole membrane paradigm is an alternative way to look at the classical dynamics of black hole horizon in terms of a fluid membrane. In this talk, I present the formal construction of the membrane paradigm for black objects in general relativity and then to Einstein-Gauss-Bonnet gravity. I also discuss the derivation of the stress-tensor for this membrane fluid and study the perturbation around static backgrounds to express the stress tensor in the form of a Newtonian viscous fluid with pressure, shear viscosity and bulk viscosity. Next I will discuss the relationship between membrane paradigm and AdS/CFT conjecture, in particular the violation of so called KSS bound for the ratio of shear viscosity to entropy density in modified gravity theories. The talk will be based on the reference: arXiv:1107.1260 .

Spatial distribution of Spontaneous Parametric Down-Converted Photons

Date: 2013-01-10
Speaker: Shashi Prabhakar
Venue: Room No. 469

Abstract

Spontaneous parametric down-conversion (SPDC) is a nonlinear optical process in which photons from a laser beam can split into two lower frequency photons. This photon pair is generated simultaneously and lies on the periphery of a circle, satisfying conservation of energy and momentum. These photon pairs are often used in quantum information experiments and applications like quantum cryptography and Bell's inequality test experiments. In this talk, I will discuss spatial distribution of the parametric down-converted photons for a Gaussian and an optical vortex as pump beams. I have observed that the spatial distribution widens linearly with increasing the size of Gaussian pump beam. The spatial distribution of intensity for a vortex shows up in its down-conversion as well and varies with the order of vortex.

2012

Pulsars as potential continuous gravitational wave emitters

Date: 2012-12-28
Speaker: Dr. Tarun Jha
Venue: Room No. 469

Abstract

Upcoming interferometric detectors such as LIGO, LISA, etc. employed to detect Gravitational Waves (GW), are also expected to detect continuous Gravitational Waves from rapidly rotating neutron stars. In the talk we will look at the perspective of locating potentially detectable GW's from pulsars on the basis of their constitution and structure in a field theoretical basis.

LHC and CMS: A look at the future

Date: 2012-12-27
Speaker: Prof. Sunanda Banerjee
Venue: Room No. 469

Abstract

-NA-

Classical dynamics as an eigenvalue problem

Date: 2012-12-20
Speaker: Prof. R. K. Varma
Venue: Room No. 469

Abstract

A probability amplitude formalism is presented which casts classical dynamics as an eigenvalue problem in the spirit of the Schrodinger formalism. The governing equation of the formalism is a first order partial differential for a probability amplitude in contrast to the second order of the Schrodinger equation. A solution for the amplitude for a given dynamical problem yields, in a rather straightforward way, the solution for the Hamilton principal function, which is a solution of the Hamilton-Jacobi equation; whence the trajectory determination follows with the H-J prescription. The linearity of the eigenvalue equation offers a great operational advantage for the treatment of perturbations as against the usual procedure using the (nonlinear) Hamilton-Jacobi equation in the action-angle framework.

Vacuum Stability constraints on the minimal singlet TeV Seesaw Model

Date: 2012-12-13
Speaker: Subrata Khan
Venue: Room No. 469

Abstract

We consider the minimal singlet seesaw model in which two gauge singlet right handed neutrinos with opposite lepton numbers are added to the Standard Model. In this model, the smallness of the neutrino masses is explained by tiny lepton number violating coupling betweenone of the singlets with the standard left-handed neutrinos. This allows one to have the the right handed neutrino mass at the TeV scale as well as appreciable mixing between the light and heavy states. This model is fully reconstructible in terms of the neutrino oscillation parameters apart from the overall coupling strengths. In this paper we show that the overall coupling strength 'y_nu' for the Dirac type coupling between the left handed neutrino and one of the singlets can be restricted by consideration of the stability bounds on the Higgs potential. Incorporating this bound, the overall coupling strength of the lepton number violating coupling can also be constrained from neutrino oscillation data. In this model the lepton flavour violating decays of charged leptons can be appreciable which can also put constraint on 'y_nu' for right-handed neutrinos at TeV scale. We discuss the combined constraints on 'y_nu' for right-handed neutrinos near TeV scale from the process mu -> e gamma and from the consideration of vacuum stability constraints on the Higgs self coupling. We also briefly discuss the implications for neutrinoless double beta decay and possible signatures of the model that can be expected at colliders.

LR symmetry Reloaded

Date: 2012-12-06
Speaker: Dr. Joydeep Chakrabortty
Venue: Room No. 469

Abstract

Left-Right symmetry is one of the popular and interesting model around TeV scale. This model is phenomenologically interesting in sens that the scale of this theory is around TeV within well reach of the Large Hadron Collider (LHC) and this model can be embedded in some high scale Grand Unified groups, like SO(10), E(6). I will discuss the impact of low energy constraints on the model parameters. The contribution to Neutrinoless Double Beta Decay process will be discussed in Type-I and Type-II seesaw dominant cases. I will briefly hint the connection and possible contribution to Lepton Flavour Violating processes in Left-Right symmetric Model.

Neutrino oscillation and present status of sterile neutrino

Date: 2012-11-08
Speaker: Monojit Ghosh
Venue: Room No. 469

Abstract

Neutrino oscillation in standard three flavor picture is now well established from solar, atmosphere, reactor, and accelerator neutrinos. The mass squared differences governing these oscillations are \tilde 10^-4 and 10^-3 eV^2. But recent experimental data is indicative of oscillations governed by mass squared differences ~ eV^2. This requires addition of a fourth light neutrino which must be a sterile. In my talk I will briefly describe the neutrino oscillation in vacuum and present status of sterile neutrino.

Recent progresses in viscous hydrodynamics and the shear viscosity of the QGP.

Date: 2012-11-01
Speaker: Dr Victor Roy
Venue: Room No. 469

Abstract

One of the most important finding in the recent years at both Relativistic heavy ion collider (RHIC) and at Large Hadron Collider (LHC) is the existence of a strongly interacting almost perfect nuclear fluid which is produced in high energy heavy ion collision. Both Lattice QCD and string theoretical calculation of the transport properties of the QCD matter at high density and temperature shows that the ratio of shear viscosity to entropy density (η/s) of the QCD matter reaches a very low value which is believed to be the lowest among all known fluids. However, these theoretical calculations contain large uncertainties. One can also estimate the value of transport coefficients (shear, bulk viscosity) of QCD matter by means of phenomenological model study e.g, relativistic viscous hydrodynamics. However, the extracted value of η/s from viscous hydrodynamics relies on some strong assumption about the initial conditions as well as other input parameters used in the model. In this talk I will mainly focus on the recent progresses in the field of viscous hydrodynamics to extract the value of η/s from the experimental data. I will also discuss some open problems related to viscous hydrodynamics which immediately needs attention in order to precisely estimate the value of $\eta/s$ from experimental data.

Present Status of Nuclear Quadrupole Moments in [39-41]-K Isotopes

Date: 2012-10-26
Speaker: Yashpal Singh
Venue: Room No. 469

Abstract

Quadrupole moment (Q) of an atomic nucleus describes the effective ellipsoidal charge distribution inside the nucleus. There is no direct experimental technique available to measure this quantity, however using nuclear models, it is possible to estimate Q of different isotopes, but currently there is no such standard nuclear model which can predict this quantity precisely. By combining measurements of atomic hyperfine structure splitting with the corresponding calculations, it is possible to infer the model independent value of Q in an atomic system. Provided both the measurement and the calculated result are very accurate, the obtained Q value will be very precise which can further used to test against the results obtained by different nuclear models. In the present, talk we shell discuss the recently reported values of Q in [39-41]-K isotopes which differ significantly from the known standard values in the literature.

Restricted equilibrium ensembles: Exact equation of state of a model glass

Date: 2012-10-10
Speaker: Prof. Deepak Dhar
Venue: Room No. 469

Abstract

We investigate the thermodynamic properties of a toy model of glasses: a hard-core lattice gas with nearest neighbor interaction in one dimension. The time-evolution is Markovian, with nearest-neighbor and next-nearest neighbor hoppings, and the transition rates are assumed to satisfy detailed balance condition, but the system is non-ergodic below a glass temperature. Below this temperature, the system is in restricted thermal equilibrium, where both the number of sectors, and the number of accessible states within a sector grow exponentially with the size of the system. Using partition functions that sum only over dynamically accessible states within a sector, and then taking a quenched average over the sectors, we determine the exact equation of state of this system.

Lee-Wick thermodynamics and its cosmological implications

Date: 2012-09-28
Speaker: Dr. Suratna Das
Venue: Room No. 469

Abstract

Lee-Wick fields were first introduced in the literature as a regulator field to tame the divergences in QED. Recently this theory is used in an extended standard model to solve the "Hierarchy Problem". In this talk the high-temperature behaviour of such Lee-Wick fields will be discussed. It would be shown that at high temperatures these Lee-Wick fields lead to negative energy density and pressure. But, being regulator fields, they are always accompanied with standard particles. Thus the total energy density and pressure of particles and their Lee-Wick partners turn out to be positive and yield a fluid with state parameter ω=1. In the second part of the talk it would be shown that such a fluid can dominate the universe just before the standard radiation domination era sets in.

In Quest of the Knots: Revisiting Chronotopic Crossroads

Date: 2012-09-27
Speaker: Dr. Annapurna Rath
Venue: Room No. 469

Abstract

Time-Space interrelationships comprise the fundamental knots of human existence. To understand the problems concealed within the conflicting yet symbiotic relationships of the time-space grid has been the core quest of theoretical enterprises across disciplines – Physics, Philosophy, and Mathematics. Creative enterprises have their own unique ways of understanding the time-space grid. The never ending dialogue between temporal and spatial axes is explored in the conceptual thread of the “Chronotopes” proposed by the Russian thinker Mikhail Bakhtin. Through this talk, I would attempt to explore the theoretical foregrounding that go into defining the chronotopes as not only conceptual categories, but rather as a step towards interdisciplinary endeavor -- an attempt to bridge the gap between philosophy and science, between “mind” and “matter”.

Theoretical Perspectives on a 125 GeV Higgs Boson

Date: 2012-09-25
Speaker: Sreerup Raychaudhuri
Venue: Room No. 469

Abstract

Assuming that the new boson recently discovered at CERN is the long-sought Higgs boson, the impact of this discovery on the Standard Model, on the future of LHC and on physics beyond the Standard Model will be discussed, from the perspective of a theorist.

A generic constraint on non-minimal coupling in inflationary cosmology

Date: 2012-09-11
Speaker: Abhishek Basak
Venue: Room No. 469

Abstract

We study the first order perturbations in a non-minimally coupled scalar field theory in the Jordan frame. It is shown by comparing the expression for the spectral index nr with the observed value that the non-minimal coupling constant ξ can have an upper bound. The bound on ξ is generic as it is obtained without assuming any specific form of potential. Source of this bound is due to the presence of λ1=f˙Hf term in the Friedman equation, where f signifies the non-minimal coupling term. From the Einstein's equation it is shown that the comoving curvature perturbation depends on parameter λ1 and it would evolve on the super horizon scales unless the bound on ξ is imposed.

Study of vacuum stability in Type-III seesaw model and its phenomenological consequences at the LHC

Date: 2012-08-30
Speaker: Gaurav Tomar
Venue: Room No. 469

Abstract

ATLAS and CMS collaboration recently announced the discovery of new boson having mass in the range of 124-127 GeV. The vacuum stability condition of the Standard Model potential with this Higgs mass puts an upper bound on the Dirac mass of the neutrinos in Type III seesaw. We have studied this constraint with the TeV scale triplet fermions. In this talk I will discuss the implications of vacuum stability bound with the neutrino less double beta decay and lepton flavour violation process.

Bose-Hubbard Models: Quantum Phases, Transitions, and Patterns

Date: 2012-08-23
Speaker: Prof. Ramesh V. Pai
Venue: Room No. 469

Abstract

In my talk, I shall present an extensive study of Mott insulator (MI) and superfluid (SF) shells in Bose-Hubbard (BH) models for bosons in optical lattices with harmonic traps. For this we apply (i) the inhomogeneous mean-field theory for 2 and 3-D and (ii) numerical density matrix renormalization group for 1-D. Our results for the BH model with one type of spinless bosons agree quantitatively with quantum Monte Carlo simulations. Our approach is numerically less intensive than such simulations, so we are able to perform calculations on experimentally realistic, large three-dimensional systems, explore a wide range of parameter values, and make direct contact with a variety of experimental measurements. We also extend our inhomogeneous mean-field theory to study BH models with harmonic traps and (a) two species of bosons or (b) spin-1 bosons. With two species of bosons, we obtain rich phase diagrams with a variety of SF and MI phases and associated shells when we include a quadratic confining potential. For the spin-1 BH model, I shall show in my talk, in a representative case, that the system can display alternating shells of polar SF and MI phases, and we make interesting predictions for experiments in such systems.

Grand unification in the light of LHC

Date: 2012-08-16
Speaker: Prof. David Miller
Venue: Room No. 469

Abstract

-NA-

The Physics Potential of future atmospheric Neutrino Detectors

Date: 2012-08-03
Speaker: Raj Gandhi
Venue: Room No. 469

Abstract

-NA-

The enigma of Cuprate high-temperature superconductivity: clues from infrared optical conductivity

Date: 2012-08-03
Speaker: Navinder Singh
Venue: Room No. 469

Abstract

Recently, K. Y. Yang, T. M. Rice, and F. C. Zhang (YRZ) have proposed an ansatz for electron Green's function in the pseudogap and superconducting states of Cuprate high temperature superconductors based upon their previous study of Renormalized Mean Field Theory (RMFT) of Cuprates. This RMFT captures the essence of Phil Anderson's Resonance Valence Bond (RVB) model of Cuprates that is based on the strong electron-electro correlation effects. We apply YRZ ansatz to compute optical conductivity using Green's function formulation of Kubo formula. In the over-doped region, optical properties of the Cuprate superconductors agree, qualitatively, with BCS form for d-wave pairing. But in the pseudogap regime a number of anomalous features appear not explainable by BCS form (due to strong electron-electron correlation). We analyze the development of pseudogap and superconducting gap with the variation of temperature and doping. Our results qualitatively agree with the measurements. An effort will be made for pedagogical presentation.

Kinetic Physics of a Turbulent Plasma (aka The Super Awesome Solar Wind)

Date: 2012-07-26
Speaker: Dr. Tulasi Parasar
Venue: Room No. 469

Abstract

It is important to study the nature of the solar wind in order to better understand space weather. The solar wind is observed to be turbulent and understanding its nature and origins requires an understanding of the kinetic physics of turbulent collisionless plasmas. We study collisionless plasma turbulence using PIC hybrid code (particle protons and fluid electrons) and discuss a few aspects of kinetic physics in such systems. We concentrate on kinetic dissipative processes and compare the relative strengths of such processes in the strong 2D limit of plasma turbulence. We also discuss the effects of expansion on solar wind plasma.

Three dimensional scattering of NN potential Argonne V18 without partial waves.

Date: 2012-07-19
Speaker: Saravanan Veerasamy
Venue: Room No. 469

Abstract

The formalism for solving the Lippmann-Schwinger equation in momentum space without partial waves, the new symbolic techniques developed for the analytical treatment of spin degrees of freedom are discussed in the seminar. A realistic NN potential Argonne V18 is used for the computation. The numerical techniques developed for efficient computation of Argonne V18 NN potential in momentum space is also discussed. Finally, the scattering observables computed in this method is presented and compared to calculations using partial waves.

Extreme values and records: from statistics to physics

Date: 2012-07-09
Speaker: Arul Laxminarayan
Venue: Room No. 469

Abstract

While the study of the ``average" leads to the Central Limit Theorem, there exists similar universal distributions for the largest and the smallest. Indeed the study of Extreme events, Large deviations and Records is of wide interest and there has been a resurgence of interest in these areas with developments from Mathematical Physics to Nonequilibrium Statistical Physics. The talk will be a very limited review of some of these aspects, and its applications to some quantum problems, especially related to quantum chaos and entanglement.

Field Theory and its applications to Cosmology (including Dark Energy)

Date: 2012-07-05
Speaker: Dr. Anupam Singh
Venue: Room No. 469

Abstract

Field theory is a fundamental tool of physics which I will argue has good reasons to be and could be the lingua franca of all physicists. Of course, if we are to test this claim then it becomes natural to demand that such a lingua franca be capable of describing the physics of our entire Universe (with perhaps some small exception made to the very early Universe). I will therefore describe field theory in the general context of a curved space-time which allows us to address a wide range of topics. I will then focus on one particular application in particular: Dark Energy. This is done not just because Dark Energy makes up about three quarters of the total energy density of the Universe but also because it is one of most fascinating mysteries of our times for which the final chapter is far from being completely finished.

Breit interaction effects in many electron atoms

Date: 2012-07-03
Speaker: Siddhartha Chattopadhyay
Venue: Room No. 469

Abstract

For high accuracy atomic calculations we need to go beyond the Coulomb interaction between two electrons. The next order of interaction is the Breit interaction, which is due to the exchange of transverse photons between two electrons. In this talk I shall discuss about the matrix elements of Breit interaction and the self consistent treatment of the frequency independent Breit interaction in many electron atoms. I will also present some results of Breit contribution at the correlation energy of closed shell atoms based on the many body perturbation theory calculations. At the end I will discuss about the implementation of Breit interaction in the relativistic coupled-cluster theory.

Dark Matter in two real scalar singlet model with Z2×Z′2 symmetry and a possible explanation of low and high mass WIMPs

Date: 2012-06-28
Speaker: Debasish Majumdar
Venue: Room No. 469

Abstract

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Probing quark gluon plasma (QGP) through electromagnetic radiations

Date: 2012-06-21
Speaker: Jajati K. Nayak
Venue: Room No. 469

Abstract

Heavy nuclei like Pb(Lead)+Pb, In(Indium)+In \& Au(Gold)+Au are collided at very high energies at Super Proton Synchrotron (SPS), CERN, Geneva and at Relativistic Heavy Ion Collider (RHIC), Brook Haven National Laboratory, USA aiming to create the novel state of matter quark gluon plasma (QGP). The matter created at the relativistic nuclear collisions emits different radiations. To diagonise the matter using the electromagnetic radiations such as photons and lepton pairs are more advantageous because of their nature of interactions with the medium they are produced. Here we discuss the photon and lepton pair productions from Pb+Pb, In+In and Au+Au collisions in terms of invariant spectra at different colliding energies. The thermodynamic informations like the initial temperature of the matter has been inferred from the evaluation of the spectra and it has been found that the inferred temperatures for the above SPS and RHIC energies are larger than the transition temperature (Tc) of the hadronic matter to QGP as predicted by lattice quantum chromodynamics (lQCD) at zero baryonic chemical potential.

Relativistic hydrodynamics and shear viscosity driven instability in Quark-Gluon Plasma

Date: 2012-06-20
Speaker: Avdhesh Kumar
Venue: Room No. 469

Abstract

In this Seminar I shall discuss about the relativistic Hydrodynamics and its application to relativistic heavy ion collisions. While keeping keeping its applications in mind, Further I shall discuss about the viscosity driven instabilities in the heavy ion collision dynamics.

Neutrino mass and multilepton signatures at LHC from a model of dimension 7 operator

Date: 2012-06-19
Speaker: Gulab Bambhaniya
Venue: Room No. 469

Abstract

Neutrino oscillation experiments suggest nonzero neutrino masses. In the Standard Model(SM) neutrinos are massless. Therefore one has to go beyond SM. There are conventional seesaw mechanisms from which scale of new physics is very high (1014 GeV) and this scale is out of collider reach. I will talk about a model in which neutrino mass at tree level can be generated from dimension 7 operator and hence the scale of new physics is at TeV scale which can be explored at collider like LHC. Then I will tell about multilepton signature from this model at LHC.

IWOP Technique and operator orderings

Date: 2012-06-18
Speaker: Nigam Lahiri Samantray
Venue: Room No. 469

Abstract

In quantum optics, operator ordering is one of the fundamental tasks in obtaining expressions for various states of light and also in calculating the expectation values of operators in these states. In this talk I will explain the newly developed IWOP (Integration Within Ordered Product) technique for arranging operators into ordered products (normal, anti-normal, Weyl)

Quadratic Gravity and Galactic Rotation Curves

Date: 2012-06-18
Speaker: Girish Chakravarty
Venue: Room No. 469

Abstract

Under the standard cosmological model based on FLRW geometry, in addition to the baryonic matter, the dark matter and the dark energy are need to be invoked to account for the total energy density of the universe. For many years it has been believed that if the gravity is governed by General Relativity field equations, there should be a substantial amount of non-luminuos (dark) matter in the galaxy and galactic clusters to account their observed dynamics.The Newtonian limit of Einstein's equations which is an excellent approximation for the solar and galactic systems cann't account the dynamics of galaxy and galactic cluster without dark matter. Einstein's General Relativity is a theory which has a linear term in the curvature R. In this seminar I shall discuss the quadratic correction to General Relativity and its implication to Galactic Rotation Curves. I shall briefly discuss about inflation in Quadratic Gravity.

Two zero mass matrices and sterile neutrinos

Date: 2012-06-11
Speaker: Monojit Ghosh
Venue: Room No. 469

Abstract

The complex Majorana neutrino mass matrix in 3 generation contains 9 parameters, all of which can not be determined experimentally. So it is proposed that it may have several zeros. According to the current data, among the possible 15 two zero's, only 7 are allowed. Now in the context of one extra sterile neutrino we tried to look what will happen to those disallowed textures. This can have significant impact on model building with sterile neutrinos.

Renormalization Group Evolution of the Non-Unitary operator

Date: 2012-06-08
Speaker: Subrata Khan
Venue: Room No. 469

Abstract

Integrating out a heavy field gives rise to effective Lagrangian containing higher dimensional operators. In the context of Type-I seesaw mechanism, integrating out the heavy right handed neutrino field leads to unique dimension five operator which gives the tree level neutrino mass term. Apart from these there are dimension six operators that can have important implications. A linear combination of two such operators gives rise to the non-unitarity in the lepton mixing matrix, UPMNS. We discuss the origin of non-unitarity at the high scale and its evolution through renormalization group running.

Nuclear Spin Dependent Parity Non-conservation from Hyperfine Interaction

Date: 2012-06-04
Speaker: Siddhartha Chattopadhyay
Venue: Room No. 469

Abstract

One source of nuclear spin-dependent (NSD) parity non-conservation (PNC) in atoms is the interference of the hyperfine interaction and the nuclear spin independent (NSI) PNC. We have examined this form of interaction in the frame work of perturbed coupled-cluster theory. In this talk I will briefly discuss in general the sources of NSD-PNC and discuss in some detail the hyperfine interaction perturbed NSI-PNC in atoms. I shall also present preliminary theoretical development to calculate the effect in alkali atoms.

Study of Vacuum Stability in Seesaw Models

Date: 2012-05-28
Speaker: Gaurav Tomar
Venue: Room No. 469

Abstract

ATLAS and CMS collaborations have narrowed down the allowed range of Higgs mass to the region 115-131 GeV. Additionally there are hints of the Higgs mass being near 125 GeV. Once this discovery is verified, we can investigate the impact of 125 GeV Higgs boson on the search of new physics beyond the Standard Model.We have taken into account the vacuum stability corresponding to a 125 GeV Higgs boson and studied its implication on Seesaw scale. In this talk, I will discuss the vacuum stability implication on Higgs mass, and Seesaw scale. We have studied the TeV scale seesaw mechanism, which can be probed at LHC and we can put bounds on the light neutrinos masses by demanding vacuum stability of 125 GeV Higgs in such models.

Development of optical parametric oscillator (OPO) for entangled photons

Date: 2012-05-25
Speaker: A. Aadhi
Venue: Room No. 469

Abstract

TEntangled photons are of great importance due to their wide applications in many fields including quantum computation and quantum communication. Such entangled photons are commonly generated by spontaneous parametric down conversion (SPDC) of laser radiation in a nonlinear crystal. However, different applications of such photons demand different features. For example, quantum computation may require entangled photons with narrow bandwidth to couple entangled photon with atom while quantum communication may require entangled sources with higher brightness. Unfortunately, single-pass SPDC of continuous-wave or femto-second pump laser do not satisfy the above requirements. Optical parametric oscillators (OPOs), made by coupling SPDC sources inside a high finesse cavity, can generate entangled photons while working below as well as above its threshold. Due to the high finesse of such optical cavities, the generated photons have very low bandwidth and also high brightness, the reason they are called cavity enhanced entangled source. On the other hand, OPOs well above threshold can also be used as alternative coherent source of light for SPDC. In this talk, I will discuss basic principles of the OPO and how it leads to generate Bell's state in polarization basis. I will also discuss about the correlation measurement and quantum tomography technique.

Stable dipoles and quadrupoles in photorefractive media

Date: 2012-05-24
Speaker: Pravin Vaity
Venue: Room No. 469

Abstract

Dipole and quadrupole vortex beams are unstable in free space propagation. The vortices in these beams annihilate each other and form crescent kind structure during propagation. However, for propagation through a photorefractive medium they form a stable structure. On the other hand dark rings of LG beam, eigensolution of wave equation in free space, break to form quadrupole vortex in the photorefractive medium. Our results show that dipole and quadrupole vortices may be the solution of nonlinear paraxial wave equation with photorefractive nonlinearity.

Rayleigh Taylor Instability in anisotropic binary Bose-Einstein Condensates

Date: 2012-05-24
Speaker: Arko Roy
Venue: Room No. 469

Abstract

The two species Bose-Einstein condensate(TBEC) is an excellent candidate to explore non-linear phenomena in superfluids. The remarkable feature of TBEC is the phase-separation, which is non-existent in single species BEC. In this talk, I will discuss about the development of interfacial instability in TBECs, namely, Rayleigh-Taylor instability(RTI). One can initiate and examine RTI in TBEC by changing the intraspecies interaction. The subsequent deformation of the interface into various patterns is an observable signature of RTI. On changing the anisotropy of the trapping potential, RTI can also be inhibited.

Precise Estimate of Multipolar Black-body Radiation Shifts in the Atomic Ion Clocks

Date: 2012-05-21
Speaker: Dillip Nandy
Venue: Room No. 469

Abstract

It is not very far to reach the 10−18 fractional uncertainty in the atomic clocks that may redefine the unit of time. Optical transitions with ultranarrow frequencies in the singly positively charged atomic ions are the ultimate choices for the atomic clocks. The major problem in setting up the best accurate atomic clock is lying in the reduction of uncertainties associated with the systematic shifts that the atomic systems undergo during the experiment.To achieve below 10−18 fractional uncertainty in the atomic clocks, it would be prerequisite to estimate the uncertainties that may occur due to the multipolar black-body radiation shifts in these clocks. In the present talk, I will discuss our recent work to estimate these shifts in Ca+ and Sr+ clocks which are under consideration at different laboratories around the world.

Entanglement verification with Bell's inequality

Date: 2012-05-18
Speaker: S.G. Reddy
Venue: Room No. 469

Abstract

Entanglement is one of the interesting phenomena in quantum mechanics. Entangled particles have a lot of applications in various fields such as quantum information, quantum cryptography, quantum teleportation, ghost imaging etc. In our laboratory, we are going to use entangled photon source for ghost imaging, in which we can obtain the spatial information of the object by quantum correlations rather than by capturing the image. To use this source, one needs to verify the entanglement between the photons. Violation of Bell's inequality is one of the best ways to prove the entanglement between two particles. In this talk, I will discuss about Bell's inequality and its violation in quantum mechanics. I will also discuss an experiment in which entangled photon source is used to show the violation of this inequality.

Cosmological Magnetic Field Generation in Higgs-Inflation Model

Date: 2012-05-18
Speaker: Moumita Das
Venue: Room No. 469

Abstract

We study the generation of magnetic field in Higgs-inflation models where the Standard Model Higgs boson has a large coupling to the Ricci scalar. We couple the Higgs field to the Electromagnetic fields via a non-renormalizable dimension six operator suppressed by the Planck scale in the Jordan frame. We show that by choosing the Higgs coupling λ(MZ)=0.132 (which corresponds to mh=126GeV in keeping with the recent measurements by ATLAS and CMS) and curvature coupling ξ(MZ)=103 we can generate comoving magnetic fields of 10−7 Gauss at present and comoving coherence length of 100kpc. The problem of large back-reaction which is generic in the usual inflation models of magneto-genesis is avoided as the back-reaction is suppressed by the large Higgs-curvature coupling.

Spontaneous parametric down-conversion process with BBO crystal

Date: 2012-05-17
Speaker: Shashi Prabhakar
Venue: Room No. 469

Abstract

Spontaneous parametric down-conversion (SPDC) is a nonlinear optical process in which photons from a laser beam, with a rather very low probability, can split into two lower frequency photons. In other words, when the input laser photons interact with a non-linear crystal (BBO), one photon of the input laser is down-converted to two lower energy photons. This photon pair is generated simultaneously and lies on the periphery of a circle, satisfying conservation of energy and momentum. If the generated photon pairs have the same polarization, it is called Type-I SPDC and if they have orthogonal polarizations, it is called Type-II SPDC. These photon pairs are often used in quantum information experiments and applications like quantum cryptography and Bell's inequality test experiments. In this talk, I will discuss about the experimental realization of SPDC and spatial distribution of the generated photon pair. I will also discuss about the experiment that we have performed and their results.

Understanding of correlation behaviors in the calculations of atomic dipole polarizabilities using an ab initio many-body perturbation theory

Date: 2012-05-17
Speaker: Yashpal Singh
Venue: Room No. 469

Abstract

It is necessary to go beyond the Hartree-Fock method (even in the relativistic case) to calculate the dipole polarizabilities in the atomic systems accurately. Understanding of the trends and dynamics of the correlation effects will be useful in the determination of these quantities more precisely. In this talk, I will explain an ab initio many-body method to evaluate dipole polarizabilities and highlight contributions from various correlations obtained using this method in few atomic systems. At the end, I will also briefly mention how the present study will berelevant to calculate the enhancement factors accurately for the studies of permanent electric dipole moments (EDMs).

Non standard spinors in inflation and dark energy

Date: 2012-05-10
Speaker: Abhishek Basak
Venue: Room No. 469

Abstract

There are very compelling reasons to believe that our universe might have undergone the phase of accelerated expansion twice in its history. The first phase of accelerated expansion was at a very early time which is called inflation and second phase started recently at around redshift z=1. Dark energy can be behind the late time acceleration. Inflation and dark energy can give us the theoretical understanding of the observation. However the exact nature of inflation and dark energy is not fully understood. There exists several models of inflation and dark energy. Among them time varying scalar field model is extensively studied. In this seminar I will talk about the possibilities of non standard spinors as a candidate of inflation and dark energy.

Cold atoms refrigeration of cold ions and cold molecule production in the presence of ions

Date: 2012-05-03
Speaker: S. A. Rangwala
Venue: Room No. 469

Abstract

We experimentally study the cooling of Rb ions in contact with Laser cooled Rb atoms. This experimental result is contrary to the widely held perception that in real ion traps, when ions and atoms have equal masses, the ions would heat out of the trap. We therefore re-examine the theory of collisional cooling of trapped ions by multiple scattering and understand the reasons for trapped ion cooling in this case. Numerical simulations of ion-atom multiple scattering bear out the experimental results. All of these studies show that the resulting ion atom system has an intrinsic stability, which is a crucial result for the prospects of physics with ion-atom mixed system. We shall then discuss the photo-association of molecules from cold atoms in the presence of ions. If time permits the most recent experiments on atom cavity coupling will be discussed, and its relevance to the molecule project explained.

Perturbed Relativistic Coupled-Cluster Theory for Atomic Calculations

Date: 2012-04-26
Speaker: Siddhartha Chattopadhyay
Venue: Room No. 469

Abstract

The coupled-cluster theory is one of the most reliable quantum many-body theory.It has been used with great success in atomic, nuclear, molecular and condensed matter physics calculations. In the present work, we have developed perturbed relativistic coupled-cluster (PRCC) theory to incorporate the effect of external electric field as a perturbation in the atomic many-body calculations. For this, the coupled-cluster equations for singles and doubles cluster operators are derived and the contributing diagrams are examined. The PRCC operators, obtained by solving the coupled non-linear equations, are then used for the dipole polarizability calculation of closed-shell systems. In this talk, we will examine the results of electric dipole polarizability for noble gas atoms, using the PRCC theory.

Photons as a probe of both isotropic and anisotropic QGP

Date: 2012-04-19
Speaker: Dr. Lusaka Bhattacharya
Venue: Room No. 469

Abstract

One of the most important issues that arises in the study of relativistic heavy-ion collisions is that of the creation of a new state of matter, quark-gluon-plasma (QGP). Since the plasma life time and volume are small, various ``probes'' of QGP detection have been proposed, such as jet-quenching, photon and dilepton production e.t.c. In this talk the prospect of photons as a possible probe is being discussed.

Coupled cluster method for Energy Spectra and Properties

Date: 2012-02-16
Speaker: Nayana Vaval
Venue: Room No. 469

Abstract

Coupled-cluster (CC) method has emerged as a state of the art method for the accurate calculation of energies and energy derivatives in the atomic and molecular systems. The linear response approach within the CC framework gives atomic and molecular properties very accurately. In this talk, results will be presented for the energy derivatives of molecules with respect to the electric, geometric and magnetic perturbations.

Hunt for the Sterile Neutrinos: Present Status and Future Prospects

Date: 2012-01-24
Speaker: Dr. Sanjib Agarwalla
Venue: Room No. 469

Abstract

First I will review the indications in favor of short-baseline neutrino oscillations, which require the existence of one or more sterile neutrinos. Then I will present the results of fits of short-baseline neutrino oscillation data in 3+1 and 3+2 neutrino mixing schemes. Finally I will discuss some powerful future probes to pin down the issue of sterile neutrino oscillation.

CMB TE polarization power spectrum estimation with non-circular beam

Date: 2012-01-12
Speaker: Dr. Subharthi Ray
Venue: Room No. 469

Abstract

Modern CMB experiments are poised for higher multipole survey of the sky and accurate measurement of the angular power spectrum Cl has been a key concern for analysing the data from these experiments. The Maximum Likelihood (ML) estimation technique is optimal but is plagued by the huge computational time and resources when approaching the higher multipoles. So, many alternative methods has been adopted of which the suboptimal but computationally fast pseudo-Cl estimator has been a very feasible approach. A semi analytical work for the pseudo-Cl method taking into account the systematic effect due to the non-circularity of the experimental beam response and has been done previously for the temperature-temperature (TT) co-relation. In the present study, we have extended this technique to the estimation of the cross power spectrum of the temperature and `E' mode (TE) polarized signal, with future plans to extend them to the EE and BB signals also.

2011

How Galilean invariant theories like Navier-Stokes are like gauge theories

Date: 2011-12-29
Speaker: Prof. Arjun Berera
Venue: Room No. 469

Abstract

I will first show how the Navier-Stokes equation (NSE),can be expressed in the same formal language as quantum field theory via thepath integral. The path integral is useful in understanding some aspects of these systems, in particular Ward identities. I show how to calculate such Ward identities for the fluid dynamics equations. This technique has long been used to study the NSE and otherGalilean invariant theories like MHD, Burgers equation and KPZ, howeverthere has been longstanding problems in implementing this method. I show that the origin of these problems is Galilean invariance leads to a redundacy in the path integral similar to that arising from gauge invariance in quantum field theories. I show how this redundacy canbe corrected via the Fadeev-Popov method and then I identify an underlying BRS symmetry in the Navier-Stokes path integral.A focal point of the problems with the Navier-Stokes path integral has been on the issue of how the vertex correlation functionrelates to the response function, and its implications for the nonlinear vertex coupling under renormalization. I show that by our gauge fixing approach, this problem no longer exists.

Quantum Transport at Nanoscale: Two Models for Energy and Charge Transfer

Date: 2011-12-12
Speaker: Dr. Malaya Banerjee
Venue: Room No. 469

Abstract

In this talk, I will describe two quantum models which are useful for elucidating energy and charge transfer phenomenology innanoscale junctions. We have employed these models for exploring the dynamics of nonequilibrium quantum dissipative systems, comprising a subsystem coupled to more than one reservoir. Besides the basic interest,practically such systems are the heart of nanodevices and crucial for future progress in nanotechnology. In the energy transfer model, we study the role of quantum effects in the thermal conduction of nonlinear systems, using a self-consistent harmonic chain model, by employing an exact numerical technique, to go beyond the linear response regime. The effect of quantum heat rectification in the mass graded system is also analyzed. In the context of charge transfer, we study the effect of an external magnetic flux on the intrinsic coherence between two electron states through a nanoscale double-dot Aharonov-Bohm interferometer. It is found that the relativephase between the two states of the double dot localizes to specific values due to decoherence.

Perfect Entanglement Transport in Quantum Spin Chain System

Date: 2011-11-08
Speaker: Dr. Sujit Sarkar
Venue: Room No. 469

Abstract

We propose a mechanism for perfect entanglement transport in anti-ferromagnetic (AFM) quantum spin chain systems with modulated exchange coupling and also for the modulation of on-site magnetic field. We use the principle of adiabatic quantum pumping process for entanglement transfer in the spin chain systems. We achieve the perfect entanglement transfer over an arbitrarily long distance and a better entanglement transport for longer AFM spin chain system than for the ferromagnetic one. We explain analytically and physically - why the entanglement hops in alternate sites. We find the condition for blocking of entanglement transport even in the perfect pumping situation. Our analytical solution interconnects quantum many body physics and quantum information science.

Nonequilibrium Phase Transitions in Active Contractile Filaments

Date: 2011-11-03
Speaker: Dr. Madan Rao
Venue: Room No. 469

Abstract

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Laser Wakefield Accelerator: Towards Gamma-Rays

Date: 2011-10-20
Speaker: Dr. Md. Ranaul Islam
Venue: Room No. 469

Abstract

Particle accelerators are used in many areas of the physical and biological sciences. The conventional accelerators employ radio-frequency electric fields to accelerate charged particles. However, the maximum electric field that can be used is limited by electrical breakdown in the beam pipes, so that accelerating particles to high energies requires a very long accelerator (the largest machine at CERN is 27km in circumference). Laser-driven plasma accelerators offer a way to make particle accelerators much more compact (centimeter range). The attraction of this method, being investigated experimentally and theoretically, lies in the propagation of intense laser pulses in a few cm under-dense plasma, which can accelerate GeV electron beams by utilizing the huge longitudinal electrostatic fields produced by displaced electrons. In a recent work, we have shown that these forces create a bubble-like ion structure, and the transverse restoring force in such ionic-background leads to the emission of intense femtosecond duration gamma-ray betatron radiation [1]. Such femtosecond duration gamma rays could be used to probe the structure of matter on unprecedented length and time scales. [1] S. Cipiccia, M. R. Islam et al. Nature Physics 2011, DOI: 10.1038/NPHYS2090

Neutrinoless Double Beta Decay and Heavy Sterile

Date: 2011-08-18
Speaker: Dr. Manimala Mitra
Venue: Room No. 469

Abstract

The experimental rate of neutrinoless double beta decay can be saturated by the exchange of sterile neutrino states, heavier than 200 MeV. This possibility has been analyzed in the context of the Type I seesaw model, performing also exploratory investigations of the implications for heavy neutrino mass spectra, rare decays of mesons, neutrino-decay search, LHC and as well as lepton flavor violation. To obtain saturating contribution from sterile neutrino states, the light- neutrino masses has to be more suppressed than the naive seesaw expectation. We have classified the cases when this condition holds true in the minimal version of the seesaw model, showing its compatibility with neutrinoless double beta rate being dominated by heavy neutrinos and with the allowed light neutrino mass spectra. The absence of excessive fine-tunings and the radiative stability of light neutrino mass matrices provides an upper bound on the heavy neutrino masses of about 10 GeV. We have extended our analysis to the Extended seesaw scenario, where the light and the heavy sterile neutrino contributions are completely decoupled, allowing the sterile neutrinos to saturate the present experimental bound on neutrinoless double beta decay.

Optical vortex and its quantum properties

Date: 2011-08-11
Speaker: Shashi Prabhakar
Venue: Room No. 469

Abstract

Vortices are ubiquitous in nature like whirlpool in water, tornadoes and hurricanes. In optics vortices are singular points in the phase distribution of the field and dark points in the intensity distribution. The wavefront is helical in the vicinity of this singular point i.e. it has screw dislocation. The number of windings of the helical wavefront in a unit wavelength of light is known as the order of vortex. There are methods based on interference and diffraction to generate as well as to detect the optical vortices. In this talk, I will discuss and explore an easy method which can provide the order of the vortex and its theoretical and experimental feasibility. Due to helicity in the wavefront, these optical vortices carry orbital angular momentum (OAM). Spontaneous parametric down conversion (a non-linear method) can be used to entangle the OAM states using the conservation of angular momentum of photons. These states provide a platform for the study of higher-dimensional entanglement which is useful in quantum information. In this talk, I will also discuss experimental methods for entanglement of OAM states and its significance.

Tribimaximal Mixing From Small Groups.

Date: 2011-08-04
Speaker: Dr. Akin Wingerter
Venue: Room No. 469

Abstract

Current experimental data on the neutrino parameters is in good agreement with tribimaximal mixing and may indicate the presence of an underlying family symmetry. For 76 flavor groups, we perform a systematic scan for models: The particle content is that of the Standard Model plus up to three flavon fields, and the effective Lagrangian contains all terms of mass dimension <=6. We find that 44 groups can accommodate models that are consistent with experiment at 3sigma, and 38 groups can have models that are tribimaximal. For A4xZ3, T7 and T13 we look at correlations between the mixing angles and make a prediction for theta13 that will be testable in the near future. We present the details of a model with theta12=33.9, theta23=40.9, theta13=5.1 to show that the recent tentative hints of a non-zero theta13 can easily be accommodated. The smallest group for which we find tribimaximal mixing is T7. We argue that T7 and T13 are as suited to produce tribimaximal mixing as A4 and should therefore be considered on equal footing. Based on arXiv:1012.2842.

Optical vortices: Finding their charge and propagation through photorefractive materials.

Date: 2011-08-03
Speaker: Pravin Vaity
Venue: Room No. 469

Abstract

We show that measurement of the topological charge and the orbital angular momentum (OAM) of optical vortex can be possible just by using a magnifying glass i.e. a spherical biconvex lens, an ubiquitous optical element found in any optics laboratory. A tilt of the the lens provides us the OAM state of the incident optical vortex. Moreover, this simple operation gives us the helicity of OAM state or the sign of topological charge as well. The experimental results have been verified with exact analytical expression. Then we present the investigation of scattering of optical vortices via beam fanning as they propagate in photorefractive materials. The measurements show that the rate of decay of the intensity depends on the order or topological charge of the vortex. This rate of decay for optical vortices is compared with that of the Gaussian beam which is found to be faster than the vortices. The experimental results are explained using dependence of the two wave mixing or beam coupling in the photorefractive materials on the degree of coherence. The coherence dependence of the beam fanning has been verified with partially coherent light also.

Minimal Textures in Seesaw Mass Matrices and their low and high Energy Phenomenology.

Date: 2011-07-28
Speaker: Subrata Khan
Venue: Room No. 469

Abstract

In the context of minimal see-saw framework, we discuss the implications of Dirac and Majorana mass matrices with texture zeros within the type I see-saw mechanism. For the Dirac mass matrices we consider 5 zero textures which we show to be the most minimal form that can successfully account for low energy phenomenology if the Majorana mass matrices are chosen minimal as well. For those, we consider both diagonal and even more minimal non-diagonal forms. Next we discuss the implications of Dirac and Majorana mass matrices in which two properties coexist, equalities among matrix elements in addition to texture zeros. Among the large number of general possibilities, only 12 patterns are found to be consistent with the global neutrino oscillation data at the level of the most minimal number of free parameters. The predictions of the allowed textures for mass hierarchy, θ13 are discussed. We also explore the possibility of having non-zero CP violation for each allowed solution. We find that only one allowed solution can accommodate both low and high energy CP violation. We discuss the prediction of this solution for leptogenesis and explore the correlation, between leptogenesis and low energy CP violation.

Phase diagram and Fluctuations using PNJL model.

Date: 2011-07-21
Speaker: Paramita Deb
Venue: Room No. 469

Abstract

The investigation of the properties of strongly interacting matter at large temperatures and densities is a very active field of research at present.In order to understand the experimantal data from RHIC, LHC, we need a proper theoretical framework. To study the properties of stronglyinteracting matter theoretically, one of the most popular model is Polyakov loopextended Nambu—Jona-Lasinio (PNJL) model. In our work we have investigated thethermodynamic properties like pressure, energy density, specific heat, speed ofsound with this model. We have also studied the phase diagram of PNJL model withsix-quark and eight-quark interactions. The introduction of eight-quark interaction shifts the critical end point (CEP) to the lower chemical potential and highertemperature, which is more closer to the lattice data. Fluctuations and correlations are important signatures of any physical system. We have calculated the fluctuations and correlations of baryon, charge and strangeness quantum number with respect to temperature. The second derivative of pressure show a steep rise near the transition region, which indicates the increase of fluctuation near the transition region. All the fourth order fluctuations show peaks near the transition temperature for six-quark and eight-quark interaction. We have also studied the spectral functions of scalar and pseudoscalar channels just above the transition temperature. The non degenracy between the spectral functions of two channels indicates that U(A)_1 symmetry is not restored just above the transition temperature.

Solitons in Nonlinear Optical Fibers and Bose Einstein Condensates Abstract:

Date: 2011-06-28
Speaker: Prof. Prasanta K. Panigrahi
Venue: Room No. 469

Abstract

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Facility to produce ultra-cold degenerate Bose and Fermi gasses

Date: 2011-06-27
Speaker: Subhadeep De
Venue: Room No. 469

Abstract

I will discuss a new apparatus at the JQI designed to produce mixture of rubidium (87Rb) Bose Einstein condensates (BEC) and degenerate Fermi gasses (DFG) of lithium (6Li) simultaneously. Currently the machine is commissioning the BEC and DFG is in pipeline. There ultra cold Bosons will initially be used for sympathetic cooling of fermions to reach the degeneracy. Degenerate Bose-Fermi mixtures support many quantum phase transitions,giving an experimental platform to study many-body statics, dynamics, andperhaps precision measurements of permanent electric dipole moment.Dynamics of high Tc superconductivity could be realized in ultracoldatoms where Fermions are paired up by boson mediated interactions:hypothetically similar to Cooper pairs. Such induced interaction isenhanced in Rb-Li mixture due to their large mass difference. Rb-Liheteronuclear molecules with large permanent electric dipole moment (4.2Debye) may serve as qubits for quantum computers. In addition, a spin-polarized, non-interacting, degenerate 6Li gas coupledto 87Rb atoms in an optical lattice will give rise to a long range, spin-dependent interactions to realize quantum magnetism and potentially supersolidity. In the experiment red-detuned lattices are far weaker, in recoil units, for 6Li as compared to 87Rb. So in the Mott phase of 87Rb – one atom per lattice site – the 6Li gas hardly feels any lattice potential. In the 87Rb Mott phase the three body recombination of Rb-Li-Li is greatly suppressed and Rb-Li-Li recombination is Pouli blocked. Thus the 10 G wide 87Rb-6Li Feshbach resonance at 1.1 kG is expected to effectively control fermion mediated interactions.

Deformed Shell Model results for double β decay

Date: 2011-05-19
Speaker: Prof. Rankanidhi Sahu
Venue: Room No. 469

Abstract

Double-β decay is a rare weak-interaction process in which two identical nucleons inside the nucleus undergo decay with or without the emission of neutrinos. Two-neutrino double beta decay is fully consistent with the standard model and has been observed in more than 10 nuclei. On the other hand the neutrino less double beta decay which involves emission of two electrons and no neutrinos has not been observed experimentally and violates lepton-number conservation. For the description of double beta decay, one should have a good nuclear structure model for reliably calculating the nuclear transition matrix elements. In the last several years. we have been using the Deformed Shell Model based on Hartree-Fock states to study the spectroscopic properties of the nuclei in the mass 80 region with considerable success. We have successfully described energy spectra, electromagnetic transition probabilities, large ground state deformation, co-existence of shapes, band crossing in many nuclei in this region. In this talk, I will discuss the application of the model to two neutrino double beta decay in 76Ge and 82Se and positron double beta decay in 78Kr, 74Se and 84Sr. In addition, I will present some preliminary results for zero-neutrino double beta decay of 76Ge.

Quantum random walks and spatial search algorithms.

Date: 2011-05-12
Speaker: Prof. Apoorva Patel
Venue: Room No. 469

Abstract

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How and why does statistical mechanics work

Date: 2011-03-31
Speaker: Navinder Singh
Venue: Room No. 469

Abstract

As the title says we want to answer the question; how and why does statistical mechanics work? As we know from the most used prescription of Gibbs we calculate the phase space averages of dynamical quantities and we find that these phase averages agree very well with experiments. Clearly actual experiments are not done on a hypothetical ensemble they are done on the actual system in the laboratory and these experiments take a finite amount of time. Thus it is usually argued that actual measurements are time averages and they are equal to phase averages due to ergodicity. Aim of the present review is to show that ergodicity is not relevant for equilibrium statistical mechanics (with Tolman and Landau). We will see that the solution of the problem is in the very peculiar nature of the macroscopic observables and with the very large number of the degrees of freedom involved in macroscopic systems as first pointed out by Khinchin. Similar arguments are used by Landau based upon the approximate property of "Statistical Independence". We review these ideas in detail and in some cases present a critique. We review the role of chaos (classical and quantum) where it is important and where it is not important. We criticise the ideas of E. T. Jaynes who says that the ergodic problem is conceptual one and is related to the very concept of ensemble itself which is a by-product of frequency theory of probability, and the ergodic problem becomes irrelevant when the probabilities of various micro-states are interpreted with Laplace-Bernoulli theory of Probability (Bayesian viewpoint). In the end we critically review various quantum approaches to thefoundations of statistical mechanics. It is argued that the eigenstate thermalization hypothesis is a special case of von Neumann's quantumergodic theory, and analogies are seen in the Khinchin's classical approach and in the von Neumann's quantum approach.

Mass measurements at the LHC with missing particle- challenges and strategies of recent times.

Date: 2011-03-10
Speaker: Partha Konar
Venue: Room No. 469

Abstract

Dark matter as non-standard fundamental particle should be weakly interacting so expected to leave no signals or energy deposits in the detectors at the LHC. Any study of this heavy, neutral, stable missing particles is complex. Recently, there has been a great deal of theoretical effort to explore the nature of dark matter particles at the LHC. In this talk I outline and discuss the mass determination techniques developed lately. I'll also cover my works on this area.

Memory-induced anomalous dynamics in a random walk model: emergence of diffusion, subdiffusion, and superdiffusion.

Date: 2011-02-25
Speaker: Dr. Niraj Kumar
Venue: Room No. 469

Abstract

A random walk model that exhibits asymptotic anomalous behavior will be presented. We will discuss how memory can influence the dynamics leading to subdiffusive, diffusive, and superdiffusive behaviors. These kinds of dynamical behaviors are well observed in real systems. Using an analytically tractable model, we will show how this diverse scenario may arise as a result of walker's response to its memory. This seems to be the first random walk model that encompasses all known dynamical behaviors.

Profile swapping and pinching in Bose-Fermi mixtures with two-color optical Feshbach resonances

Date: 2011-02-24
Speaker: Sandip Gautam
Venue: Room No. 469

Abstract

We examine the density profiles of the quantum degenerate Bose-Fermi mixture of $^{174}$Yb-$^{173}$Yb, experimentally observed recently, in the mean field regime. In this mixture there is a possibility of tuning the Bose-Bose and Bose-Fermi interactions simultaneously using two well separated optical Feshbach resonances, and it is a good candidate to explore phase separation in Bose-Fermi mixtures. Depending on the Bose-Bose scattering length $a_\BB$, as the Bose-Fermi interaction is tuned the density of the fermions is pinched or swapping with bosons occurs.

CONVERTING SPACE INTO TIME: HOW TO ORDER THE DISORDERED (Studies in the Effective Medium Approximation in Transport Theory)

Date: 2011-02-01
Speaker: V. M. Kenkre
Venue: Room No. 469

Abstract

Effective medium theory of transport in disordered systems, whose basis is the replacement of spatial disorder by temporal memory, is extended in several practical directions. A transformation procedure is developed to deduce, from given distribution functions characterizing the system disorder, explicit expressions for the memory functions. The extent of the agreement of effective medium theory predictions with numerically computed exact results is explored and a number of new results are discussed including emergence of a percolation threshold, of spatially long range transfer rates, size effects, and pausing time distributions in continuous time random walks corresponding to the effective medium memories.

Classical-Quantum relationship--a new point of view

Date: 2011-01-27
Speaker: Prof. R. K. Varma
Venue: Room No. 469

Abstract

Following Dirac's conjectural comments that a solution of the Hamilton-Jacobi equation, the principal function, represents a 'family' of solutions of a classical dynamical problem, we develop an equation which describes what we term as the "Hamilton-Jacobi flow." This evolves along the characteristics of the Hamilton-Jacobi equation. A Hilbert representation of the flow is then constructed and it is shown that it yields a generalized set of Schrodinger equations describing this flow. Paradoxically,these together represent classical dynamics while only one of them is identified as the quantum mechanical Scrodinger equation. The nature of this relationship is then discussed.

Theoretical study on the Aluminium Nuclear Magnetic Resonance spectroscopy

Date: 2011-01-20
Speaker: Chengbin Li
Venue: Room No. 469

Abstract

In my talk, I will introduce our semi-empirical molecular mechanical study on the Al Nuclear Magnetic Resonance (NMR) spectroscopy of zeolites. In this procedure, we consider classical molecular mechanics to describe the zeolite and use quantum mechanics to study the dynamics in the active Al sites. I will present our theoretical results and compare them with other available theoretical and the experimental results. I will also show that a partial identification of Al sites in the zeolite framework is possible.

Computational and Numerical Algebraic Geometry and Their Applications in Theoretical Physics

Date: 2011-01-06
Speaker: Dhagash Mehta
Venue: Room No. 469

Abstract

Nonlinear equations arise in theoretical physics naturally and frequently. In general, it is always difficult to solve (i.e., get ALL solutions, either exactly or numerically) them. However, if the non-linearity of the equations is polynomial-like, then one can use the computational and numerical algebraic geometry methods developed recently to solve the equations exactly or numerically, respectively. I will take an example of the XY model Hamiltonian, a well-known spin glass system, to illustrate how the methods can be used to get all stationary points. I will then briefly mention the other applications of these methods to many problems in theoretical physics (e.g., minimizing a classical hamiltonian) and non-linear dynamics (e.g., solving steady state equations of the neural models and models exhibiting synchronization).

Majorana fermions in condensed matter systems

Date: 2011-01-04
Speaker: Dr. Pavan Hosur
Venue: Room No. 469

Abstract

Majorana fermions, despite having been in the news for several decades, have not been observed conclusively so far. Although they were first proposed as candidates for neutrinos in high-energy physics, a rather different kind of realization of them has been discussed lately in condensed matter physics, where they can appear in certain superconductors. Most of these proposals, though, either require considerable amount of engineering or involve types of materials that have not yet been discovered. In our work, we propose a way to obtain Majorana states simply by passing a magnetic field through some superconductors, and give several real material examples. An easy route towards obtaining these superconductors is by doping insulators known as 'topological insulators', which have attracted tremendous theoretical and experimental recent attention in the condensed matter community themselves. However, we derive more general criterion which will allow even non-topological insulator-based superconductors to give rise to Majorana states. Additionally, the phase transition between phases with and without Majorana modes takes place through a vortex in the superconductor, which to our knowledge, is the first example of a phase transition inside a topological defect.

2010

Byzantine Astronomy From A.D. 1300

Date: 2010-12-10
Speaker: Prof. Emmanuel A. Paschos
Venue: Room No. 469

Abstract

A Byzantine article from the 13th century contains advanced astronomical ideas and pre-Copernican diagrams. The models are geocentric but contain improvements on the trajectories of the Moon and Mercury. This talk presents several models and compares them briefly with the Astronomy of Ptolemy, Arabic Astronomies of that time and the heliocentric system.

Implications of CP violating 2HDM in B Physics

Date: 2010-12-09
Speaker: Bhavik Kodrani
Venue: Room No. 469

Abstract

New sources of CP violation can arise in general two Higgs doublet models in three ways. (1) From the mixing between scalar and pseudo-scalar. (2) From the phases in couplings of tree level flavour changing neutral currents. (3) From the phases in charged Higgs couplings to the fermions. Consequences of all these CP violating effects in the general 2HDM in B systems will be discussed. In particular, we will discuss the possibility of explaining the large CP violating phase observed in Bs mixing in 2HDM.

Dark Matter

Date: 2010-12-02
Speaker: Prof. Subhendra Mohanty
Venue: Room No. 469

Abstract

I will give a summary of the status of dark matter detection by direct scattering in terrestrial experiments and evidence for dark matter from cosmic ray observations.

Beyond the Standard Model physics and it's cosmological consequences.

Date: 2010-11-25
Speaker: Sudhanwa Patra
Venue: Room No. 469

Abstract

In spite of remarkable success of Standard Model in describing the low-energy phenomena, there are many motivations to study BEYOND STANDARD MODEL(BSM) Physics. I will discuss Supersymmetric Left-Right Theory and SU(5) Guts as the BSM physics in the context of RG running, neutrino mass and Spontaneous Parity Violation. As a consequences of BSM physics, I will talk about electromagnetic leptogenesis as a way to explain the origin of baryon asymmetry of the present Universe. Instead of standard scenario of Leptogenesis, there is a different kind of leptogenesis is possible via the out of equilibrium decay of heavy right handed Majorana neutrino through 5D and 6D-EMDM couplings: i.e, NR−>νγ and NR−>νγϕ. Also resonant electromagnetic leptogenesis(at the TeV scale) and its connection to neutrino mass will be discussed.

Emergent gravity and matrix models

Date: 2010-11-19
Speaker: Prof. M. Sivakumar
Venue: Room No. 469

Abstract

Light neutrinos from massless texture and below TeV seesaw scale

Date: 2010-11-18
Speaker: Prof. Amitava Raychaudhuri
Venue: Room No. 469

Abstract

If there is new physics around the TeV scale the Type I seesaw mechanism for small neutrino mass requires fine-tuned cancellation among different contributions to the neutrino mass matrix. We generalize the possible structures of the 6 x 6 neutrino mass matrix for which neutrinos are massless in the tree approximation and such cancellations are possible. We discuss the possible symmetries for such structures of the mass matrix. Finally, we illustrate how symmetry breaking and loop corrections may lead to small neutrino masses. A seesaw scale below TeV for right-handed Majorana neutrinos might thus be admissible.

Pancharatnam, Bargmann and Berry Phases - a Retrospective

Date: 2010-10-28
Speaker: Prof. N. Mukunda
Venue: Room No. 469

Abstract

The work of Pancharatnam in classical polarisation optics, of Wigner and Bargmann on the representation of symmetry operations in quantum mechanics, and of Berry in adiabatic cyclic quantum evolution, will be described from a historical perspective. The interconnections among the three sets of ideas will be highlighted. Later important developments, including contributions from India, will be outlined.

Bose Einstein Condensation: A Quantum many-body approach

Date: 2010-09-23
Speaker: Dr. Barnali Chakrabarti
Venue: Room No. 469

Abstract

The discovery of Bose-Einstein condensation in cold alakali atomic vapors and subsequent experiments including the strong interaction regimes is one of the most successful and interesting research area since last decade. A lot of theoretical works are going on in different directions to explain experimental results and predict new ones. The widely used approach is the mean field Gross-Pitavskii equation. Although it is a very convenient approach to predict gross property of the condensate, still the uncorrelated mean field equation using just contact delta interaction ( with a singularity in the origin in 3D) is questionable and deserves full quantum many body calculation using interatomic correlations and realistic interaction. Very recently, we have applied a very convenient ab-initio many body approach with certain approximation, which include two body correlations and realistic van del Walls interaction. We correctly describe ground state properties, collective excitations and also thermodynamic properties of dilute BEC in JILA trap and it can handle quite large number (approx. 15000) of bosons. Our approach has also been spectacularly successful in reproducing the controlled collapse experiment of attractive BEC in JILA trap and calculated stability factor which is in nice agreement with experiment.

The magic of earth matter effects in neutrino propgation

Date: 2010-09-16
Speaker: Dr. Srubabati Goswami
Venue: Room No. 469

Abstract

In this talk I will consider propagation of neutrinos through earth's matter and will explain some salient features of this. Specifically I will discuss the baseline 7500 km which is known as the magic baseline. I will also discuss another recently proposed baseline (2540km) which is called the bi-magic baseline. I will show the constraints that can be obtained on neutrino oscillation parameters with a 2540 km neutrino factory experiment.

Quantum dynamics of excitation energy transfer in photosynthesis: Master equation approach.

Date: 2010-09-09
Speaker: Dr. Navinder Singh
Venue: Room No. 469

Abstract

We show that the exciton motion in excitation energy transfer (EET) in photosynthesis involves non-Markovian effects and the Markovian Redfield theory cannot explain the observed coherence effects in EET. In the literature people have wrongly made the Markovian approximation in the parameter regime, in which the quantum dynamics is highly non-Markovian. The approach used here is standard one: time evolution equation for the reduced density matrix (Projection operators and quantum master equations). We have made use of the 2nd Born quantum master equation (time convolution form) and able to integrate (both in energy and site representation) this integro-differential equation with auxiliary function method. We are able to know precisely upto what value of re-organization energy and the decay rate of the phonon auto-correlation function, one can use the Markovian Redfield theory and second order approximation. We have also investigated the presence of initial coherences as the laser pulse not only excites the populations but also the coherences, this has not been taken into account in previous investigations.

Type-I seesaw mechanism for quasi-degenerate neutrinos & its SO(10) unified description.

Date: 2010-08-26
Speaker: Mr. Ketan Patel
Venue: Room No. 469

Abstract

All neutrinos being quasi-degenerate is still an allowed possibility. It is non-trivial to accommodate such possibility within the conventional pictures of neutrino mass generation. I will discuss symmetries and scenarios leading to quasi-degenerate neutrinos in type-I seesaw models. Implementation of such scheme in SO(10) based models and its consequences will also be discussed.

Chiral symmetry breaking in strong magnetic background.

Date: 2010-08-21
Speaker: Bhaswar Chaterjee
Venue: Room No. 469

Abstract

Extreme Events on Complex Networks.

Date: 2010-08-05
Speaker: Mr. Vimal Kishore
Venue: Room No. 469

Abstract

Extreme events occur rarely in nature. They have great importance due to their large socio-economic impact on the society. In this talk, we will focus on extreme events taking place on complex networks. Traffic jams, internet slowdowns, floods in river network are few examples of such events on networks. We study simple random walk model on scale-free network and show that extreme events are more likely to occur on nodes with lower degree in comparison to higher degrees nodes. This result can be useful in designing the transport networks which can handle such extreme events.

Thermal photons in QGP and non-ideal effects.

Date: 2010-07-20
Speaker: V. Sreekanth
Venue: Room No. 469

Abstract

We study the effect of non-ideal equation of state (EoS) and bulk viscosity on the thermal photon signals produced from the Quark Gluon Plasma produced during the relativistic heavy ion collisions. We use one dimensional boost-invariant second order relativistic hydrodynamics to find proper time evolution of the energy density and the temperature.The effect of bulk viscosity and non-ideal equation of state are taken into account in a manner consistent with recent lattice QCD estimates. We observe that the expanding plasma with a non-ideal EoS- which is important near the phase-transition point, can significantly slow down the hydrodynamic expansion and thereby increase the photon production-rates. We also analyze the interesting phenomenon of bulk viscosity induced cavitation making the hydrodynamical description invalid. It is shown that ignoring the cavitiation phenomenon can lead to a very significant overestimation of the photon flux. It is argued that this feature could be relevant in studying signature of cavitation in relativistic heavy ion collisions.

Desynchronization bifurcation of coupled nonlinear dynamical systems.

Date: 2010-07-19
Speaker: Suman Acharaya
Venue: Room No. 469

Abstract

We analyse the desynchronization bifurcation in the coupled chaotic systems with the specific example of coupled R矣ssler systems. After the desynchronization bifurcation the attractors of the coupled systems split into two and start moving away from each other with a square root dependence on the parameter. We define system transverse Lyapunov exponents and in the desynchronized state one of them is positive while the other is negative. This means that the attractor of one system is trying to fly away while that of the other system is holding it. We give a simple model of coupled integrable systems which shows a similar phenomena. This model can be treated as a normal form for the desynchronization bufurcation. We conclude that the desynchronization bifurcation is a pitchfork bifurcation of the transverse manifold.

Optical Vortices - Study of Coherence.

Date: 2010-07-16
Speaker: Ashok Kumar
Venue: Room No. 469

Abstract

Vortices are ubiquitous in nature; therefore exploring their properties carries a lot of significance to many branches of physics. We, on our part, have embarked on the study of the coherence properties of vortices in light known as optical vortices. These are the light beams with helical wavefront and phase singularities in the optical field. In the present talk, I will discuss field and intensity correlation properties of optical vortices. We will see that the second order coherence i.e. intensity correlation of vortices scattered by a rotating ground glass decays faster than that of a Gaussian laser beam. We observe a linear relationship in correlation time and order of the vortex.

Non-Gaussianity as a signature of thermal initial condition of inflation.

Date: 2010-07-15
Speaker: Suratna Das
Venue: Room No. 469

Abstract

Primordial non-Gaussianity is an unique feature of the CMBR, measuring which one can distinguish between the existing inflationary models. I will discuss in this presentation the effects of a pre-inflationary radiation era on primordial non-Gaussianities. We found in our work that presence of such a radiation era enhances the fNL and τNL by a considerable amount and yields large enough primordial non-Gaussianities that can be measured by future experiments like PLANCK. I will also discuss the methodology to calculate non-Gaussinities in such a scenario and the results thus obtained.

Dark Energy: constant or time variable?

Date: 2010-07-14
Speaker: Prof. Bharat Ratra
Venue: Room No. 469

Abstract

Experiments and observations over the last decade have persuaded cosmologists that (as yet undetected) dark energy is by far the main component of the energy budget of the universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions.

SUSY Dark Matter in the light of cosmic ray experiments.

Date: 2010-07-13
Speaker: Soumya Rao
Venue: Room no. 469

Abstract

We study a supersymmetric model for Dark Matter (DM) which explains the PAMELA positron and antiproton fluxes. We consider Sommerfeld enhancement to be the source for the boost factor required in the cross section to explain the PAMELA result. We also consider the possibility of obtaining the correct relic density using a Sommerfeld enhancement factor, thus having a consistent theory which obeys constraints from relic density as well as indirect detection of DM.

Probing anomalous VZH interactions at ILC with polarized beams.

Date: 2010-06-25
Speaker: Pankaj Sharma
Venue: Room No. 469

Abstract

In this talk, I will talk about how International Linear Collider (ILC) can be utilized to its full potential using polarization (longitudinal or transverse) of both electron and positron beams, which are expected to be available at the ILC, to probe anomalous VZH couplings, where V is electroweak neutral gauge bosons i.e., Z or photon, in the process e+ e- --> HZ. I will discuss the sensitivity of simple observables like forward backward asymmetry, azimuthal asymmetries and cross sections to these anomalous couplings using various combinations of beam polarizations.

Condensation temperature of bosons for the quartic confining potential and ground state geometry of binary condensates.

Date: 2010-04-13
Speaker: Prof. S. Gautam
Venue: Room No. 469

Abstract

We calculate the critical temperature $T_c$ of non-interacting bosons, including the effect of finite boson number, at which normal to BEC transition occurs for the quartic confining potential. For two species BECs (TBECs), we show that the ground state interface geometry in the phase separated regime undergoes a smooth transition from planar to ellipsoidal to cylindrical geometry. This occurs for condensates with repulsive interactions as the trapping potential is changed from prolate to oblate. The correct ground state geometry emerges when the interface energy is included in the energy minimization, whereas energy minimization based on Thomas-Fermi approximation gives incorrect geometry. We also examine WKB approximation to calculate $p$-wave scattering length which describes the low energy scattering properties of identical fermions.

Chip-based sources of entangled photons from a single quantum dot.

Date: 2010-04-01
Speaker: Dr. Pradyumna Pathak
Venue: Room No. 469

Abstract

A source of polarization-entangled photon pairs has wide uses in quantum optics, leading to applications such as quantum computation, quantum information processing, quantum cryptography, and quantum metrology. There has been considerable progress for developing scalable sources of entangled photons using single quantum dots. In semiconductor quantum dots, entangled photons are typically generated in a biexciton-exciton cascade decay. However, the entanglement between the generated photons is limited by inherent cylindrical asymmetries and various dephasing processes. The cylindrical asymmetries produce fine structure splitting (FSS) in the exciton states; as a result, the emitted x-polarized and y-polarized photon pairs become distinguishable in frequency, and the entanglement between the photons is largely destroyed. In this talk, I will discuss "within generation" and "across generation" of entangled photons when a quantum dot is coupled in a photonic crystal cavity. I will also show that the entanglement can be distilled in both cases using a simple spectral filter.

Diffuse UHE Neutrino Fluxes and Physics beyond the Standard Model

Date: 2010-03-31
Speaker: Prof. Raj Gandhi
Venue: Room No. 469

Abstract

We study spectral distortions of diffuse ultra-high energy (UHE) neutrino flavour fluxes resulting due to physics beyond the Standard Model (SM). Even large spectral differences between flavours at the source are massaged into a common shape at earth by SM oscillations, thus, any significant observed spectral differences are an indicator of new physics present in the oscillation probability during propagation. Lorentz symmetry violation (LV) and Neutrino decay are examples, and result in significant distortion of the fluxes and the well-known bounds on them, which may allow UHE detectors to probe LV parameters, lifetimes and the mass hierarchy over a broad range.

Higher Dimensional Effect on a Torsion Balance.

Date: 2010-03-25
Speaker: Dr. M. Azam
Venue: Room No. 469

Abstract

Dark Matter in SUGRA Models with Universal and Nonuniversal Gaugino Masses.

Date: 2010-03-15
Speaker: Prof. D. P. Roy
Venue: Room No. 469

Abstract

Networks and Emergence.

Date: 2010-03-08
Speaker: Soumen Roy
Venue: Room No. 469

Abstract

Networks are used to model a wide range of complex systems. Especially, their paramount importance in the emergent field of Systems Biology is now universally accepted. We outline systematic methods to show how and why multiple network metrics should be studied in parallel. Specifically, we uncover connections between phenotypes of various biological organisms and their network architecture. We also present new models and mechanisms of network growth and demonstrate how they shed insight in analyzing and modeling various systems.

Wavelet analysis of Nonlinear oscillations.

Date: 2010-03-04
Speaker: A. N. Sekar Iyengar
Venue: Room No. 469

Abstract

Fourier analysis is very popular technique to which everyone resorts to in the analysis of fluctuations/oscillations: fluids, plasmas, finance, EEG,ECG, earthquakes etc. But the disadvantage of this technique does not yield time information which is overcome by wavelet analysis. Wavelet transforms have become quite popular in different fields of research from which one can derive both time-scale(or inversely frequency) information. We shall show how we have been able to derive information regarding presence of nonlinerity as well as the chaoticity of the system through some data obtained from our plasma experiments and from foreign exchange rates.

The Top Way to the Bottom of Things.

Date: 2010-03-02
Speaker: Prof. Debajyoti Chaudhuri
Venue: Room No. 469

Abstract

With the first papers from the LHC being published, it is imperative that we examine what we know of fundamental physics and what future experiments (primarily those at the LHC) can tell us about. In this talk, I argue that the study of the Top quark can potentially reveal much, mentioning alongside what all we still do notknow.

Exotic Nuclei: Large-scale shell model calculations.

Date: 2010-02-18
Speaker: Dr. Praveen C Srivastav
Venue: Room No. 469

Abstract

The neutron-rich nuclei in the fp and fpg shell region (Fe to Zn nuclei) are at the focus of attention of nuclear physics community at present-- thanks to Radioactive Ion Beam facilities for exploring this region widely. Unstable nuclei in this region exhibit many new phenomena such as melting of existing magic numbers and appearance of new ones, softening of core at N=28, interplay of collective and single particle properties etc. In this seminar, I am going to present our results of modern large scale shell model calculations for these two regions.

A Leptophilic Model Explaining Neutrino Masses and Dark Matter.

Date: 2010-02-16
Speaker: Dr. Michael A Schmidt
Venue: Room No. 469

Abstract

Despite all its triumphs, the Standard Model (SM) of elementary particles fails to explain two recent discoveries: dark matter and tiny but nonzero neutrino masses. In this talk, I will propose a possible connection between neutrino masses and dark matter in an economic extension of the SM and discuss its phenomenological implications. Besides constraints from dark matter search experiments, bounds from lepton flavour violation and electroweak precision measurements are outlined.

Modern Shell Model.

Date: 2010-02-04
Speaker: Prof. V. K. B. Kota
Venue: Room No. 469

Abstract

Progress in the last four decades in developing shell model codes starting from the codes for p-shell nuclei with matrix dimensions ~10-20 to the pf-shell and beyond with dimensions ~ 100 million or more and the ingredients needed for a successful shell model calculation will be discussed.

Some results using simple coupled maps

Date: 2010-01-21
Speaker: Some results using simple coupled maps
Venue: Room No. 469

Abstract

In this seminar we discuss three results dealing with some simple nonlinear coupled maps. First, we show that that the stationary density of the coupled tent map has a fractal character. Then we introduce a new method suited for the global analysis of synchronization in a coupled nonlinear system. We demonstrate it using coupled tent maps. Finally, we study coupled logistic maps whose coupling strengths change according to a learning rule. We study the effect of this learning on the network topology. This result has relevance to Neuroscience.

2009

Quantum Statistics of Light From Optical Parametric Oscillators

Date: 2009-12-10
Speaker: Prof. Surendra P. Singh
Venue: Room No.469

Abstract

Study of cold and dense neutron star matter

Date: 2009-12-03
Speaker: Dr. Debarati Chatterjee
Venue: Room No. 469

Abstract

Neutron stars are unique astrophysical laboratories to study cold and dense matter under extreme conditions. It is been suggested that strange matter such as hyperons, kaons or even deconfined quarks can appear at the high densities prevailing in the neutron star core. When a neutron star is perturbed, it can be set into non-radial oscillations, emitting gravitational waves at characteristic frequencies of its quasi-normal modes. The pulsation modes are classified according to the different restoring forces, such as Coriolis restored r-modes. R-modes are unstable to gravitational radiation reaction driven instability in rapidly rotating neutron stars. The detection of gravitational waves emitted by an oscillating star may soon become possible with the upcoming generation of gravitational wave detectors. It is conjectured that r-mode oscillations could be effectively suppressed by bulk viscosity due to non-leptonic weak processes involving exotic matter in the neutron star interior. We used relativistic field theoretical models to construct the equations of state and calculated the coefficient of bulk viscosity due to non-leptonic weak interactions involving various compositions of strange neutron star matter. The influence of exotic particles and their associated bulk viscosity on the gravitational radiation reaction driven instability in the r-modes was investigated. Another pulsation mode is the pure space-time mode known as w-mode. Axial w-modes carry information on both the structure of the neutron star matter and the nature of hadronic interactions. We studied the problem of extracting information about the composition and equation of state (EoS) of the neutron star interior using axial w-modes, whose frequency and damping time can be extracted from the observation of gravitational waves.

Generation of high-power, continuous-wave, optical radiation from visible to near-infrared

Date: 2009-08-20
Speaker: Goutam K. Samanta
Venue: Room No. 469

Abstract

Although lasers have been in use for nearly 50 years, unavailability of the suitable laser gain materials precluded the development laser systems that can cover many regions of the optical spectrum, from ultraviolet (UV) and visibl to the near and mid-infrared wavelength range, with potential applications in the fields such as spectroscopy, remote sensing, trace gas detection, and many more. On the other hand, nonlinear optics has evolved as a powerful technique to generate tunable optical radiation inaccessible to ordinary lasers. Based on nonlinear effect, the optical parametric oscillators (OPOs) has become a standard device to convert a fixed laser wavelength to wide band of coherent radiation ranging from visible to far-IR. Development of continuous-wave (cw) OPOs in singly-resonant oscillator (SRO) configurations, the focus of this talk, is challenging due to the high threshold pump power (several watts). In addition, with visible pumping, photorefractive effect and thermal lensing effects become important issues to overcome. Therefore, the realization of practical cw SROs requires optimal cavity design, suitable nonlinear materials, and high-power laser with high spectral and spatial quality. In this talk, I will describe the development of advanced SRO systems based on the latest generation of quasi-phase-matched nonlinear materials, which are capable of providing cw, single-frequency radiation at unprecedented power levels exceeding 1 W and broad spectral coverage in the visible and near-infrared wavelength regions. The talk will also include some background on the origin of nonlinear optical effects, crystal optics, phase-matching and applications of OPO sources. visible to near-infrared