August-2017 Seminar

Title : TBA

Date : 31-08-2017
Time : 16:00:00
Speaker : Dr. Uma Shankar Gupta (University of Allahabad)
Area : Theoretical Physics
Venue : Room No. 469

Abstract

TBA

Date : 24-08-2017
Time : 16:00:00
Speaker : Dr. Sukla Pal
Post Doctorate Fellow
Area : Theoretical Physics
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.

Date : 17-08-2017
Time : 16:00:00
Speaker : Dr. Gauhar Abbas (PRL
Area : Theoretical Physics
Venue :

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.

Title : Neutrino Astronomy with IceCube Neutrino Detector

Date : 17-08-2017
Time : 16:00:00
Speaker : Dr. Debanjan Bose
Area : Astronomy & Astrophysics Division
Venue : Room - 113/114, Thaltej Campus

Abstract

IceCube is a cubic-kilometer neutrino observatory buried deep in the ice sheet at the geographic South Pole. A total of 5160 Digital Optical Modules (DOMs) are deployed on 86 strings forming a three dimensional detector array. Over the past decade, South Pole has emerged as a leading site for neutrino astronomy, particle astrophysics and neutrino physics. IceCube's discovery of a diffuse flux of astrophysical neutrinos started a new era of neutrino astronomy. In this talk I will describe IceCube neutrino detector and some of it's results. Also, I will give an overview of plans to upgrade IceCube.

Date : 10-08-2017
Time : 16:00:00
Speaker : Mr. Vibhuti Bhusan Jha (SAC)
Area : Theoretical Physics
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.

Title : Collision (de)excitation of molecules in Interstellar medium : NH as a case study

Date : 10-08-2017
Time : 00:10:30
Speaker : Mr. Ragav Ramachandran
Area : Atomic, Molecular and Optical Physics
Venue : Room No. 006, PRL Thaltej

Abstract

NH and ND molecules play a very crucial role in the prestellar chemistry as they act as intermediate during the formation of the ubiquitous ammonia. Hence there is a need for the accurate modelling of their abundances in space to better understand the physical conditions and the chemical evolution of the prestellar core. We consider H2 and He as the colliding partners as they are dominant species in the interstellar medium and significantly contribute to the excitation of both NH and ND. The earlier studies on the NH-He system were performed using a potential energy surface (PES) which was proved to be relatively close. However, they did not consider the vibration of the NH bond which can impact the magnitude of the collisional data. Hence we take into account the vibration of the N-H molecules.We are also working on the NH-H2 system and preliminary rate coefficients which are first of its kind. These results would be of particular interest because they are first for this system and they should contribute significantly impact the astrophysical modelling by allowing an accurate determination of the NH abundance in the space.

Title : Radioactive sources of APXS on-board Chandrayaan-2: Implications

Date : 10-08-2017
Time : 16:00:00
Speaker : Mr. Mithun N. P. S.
Area : Astronomy & Astrophysics Division
Venue : Room - 113/114, Thaltej Campus

Abstract

Alpha Particle X-ray Spectrometer (APXS) experiment on-board Chandrayaan-2 rover employs the techniques of X-ray Fluorescence (XRF) and Particle Induced X-ray Emission (PIXE) to measure the elemental abundances of Lunar surface close to the landing site. For this purpose, APXS carries six Cm-244 sources of total activity of 30 mCi, which emits X-rays as well as alpha particles. Usage of these high activity sources calls for certain special considerations in the design of the instrument, assembly, characterization and calibration, transportation and spacecraft level integration tests to ensure the safety of people around and better performance of the instrument. In this talk, we will discuss the aspects of radiation safety, radiation dose calculations, measurements, and limits, transportation regulations etc in the context of APXS.

Date : 08-08-2017
Time : 16:00:00
Speaker : Dr. Abhaya Kumar Swain (PRL)
Area : Theoretical Physics
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.

Date : 08-08-2017
Time : 16:00:00
Speaker : Mr. P. Kiran Kumar
Senior Research Fellow
Area : Geosciences Division
Venue : Ground Floor Lecture Hall

Abstract

The Indian Summer Monsoon (ISM) plays an important role in the climate of the southeast Asia. Central Indian plains receive ~80% of the annual rainfall during the summer monsoon. The rainfall over India is affected by many ocean-atmospheric coupled processes which lead to phenomenon like El-Nino Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Madden Julian Oscillation (MJO) which occur at inter-annual to intra-seasonal time scales. These coupled processes control the strength of the monsoon and the climate of the Indian subcontinent. In this seminar, I will discuss the spatial patterns of ISM in response to ENSO at monthly to seasonal time scales. A comparison of rainfall with paleoclimate data and its implications will be presented.

Title : Single Spins in Diamond - Precision Metrology at the Nanoscale

Date : 04-08-2017
Time : 00:16:00
Speaker : Dr. Gopalakrishnan Balasubramanian
Area : Atomic, Molecular and Optical Physics
Venue : G F Lecture Hall

Date : 03-08-2017
Time : 16:00:00
Speaker : Dr. Rathin Adhikari (CTP, University of Delhi)
Area : Theoretical Physics
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.

Date : 01-08-2017
Time : 16:00:00
Speaker : Dr. Sudip Kumar Haldar (Kolkata West Bengal)
Area : Theoretical Physics
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.