Theoretical Physics Seminars

"Over the last two decades, oxide heterointerfaces have shown emergent properties different from their constituents: the sum being more than the sum of the parts. At the hetero-interface, two insulating oxides SrTiO3 and LaAlO3, produce a highly conductive two-dimensional electron liquid (2DEL). This 2DEL exhibits exciting new phenomena such as finite-momentum triplet superconductivity coexisting with inhomogeneous ferromagnetism. For reasonably strong disorder, the system breaks up into mutually excluded regions of superconductivity and ferromagnetism, ruling out FFLO states [1]. This electronic phase-separation accounts for the unusual coexistence of superconductivity and ferromagnetism observed at the interface. A Monte-Carlo calculation shows a clustering of vacancies at low temperatures [1] which sheds light on ill-understood phenomena like carrier freeze-out at low temperature and pseudo-gap in the superconducting state. Phase-transition to topological superconductivity is driven by perpendicular magnetic fields while gapless topological excitations [2], such as Majorana fermions, appear at the core of a vortex. Possible scenarios for anomalous Hall effect and spin Hall effect with changing Fermi surface topology (a Lifshitz transition) are outlined [3]. The observation of transient superconductivity above nominal Tc, implying a 'hidden' superconducting order [4,5], is explained. A recently proposed polar-polar interface of LaVO3/KTaO3 is shown [6] to harbour no topological semi-metal/insulator state while the magnetic order, transport and FS topology are found to depend on the number of layers of KTO."

References:
[1] N. Mohanta, A. Taraphder, J. Phys. Cond. Mat. 26, 025705 (2014)
[2] N. Mohanta and A. Taraphder, Europhys. Lett. 108, 60001 (2014)
[3] N. Mohanta, S. Bandyopadhyay, S. Lal and A. Taraphder, arXiv:1407.6539 (2014)
[4] Shelender Kumar, Gopi Nath Daptary, Pramod Kumar, Anjana Dogra, N. Mohanta, A. Taraphder, R. C. Budhani, Aveek Bid, Phys. Rev. B 95, 174502 (2017)
[5] N. Mohanta and A. Taraphder, Phys. Rev. B. 92, 174531 (2015)
[6] Shubham Patel, Narayan Mohanta, Snehasish Nandy, Subhendra D. Mahanti, A Taraphder, Phys. Rev. B 110, 054402 (2024) (2023)

Beyond conventional magnetism, a new unconventional magnetic order, altermagnetism with alternating spin splitting along the momentum path, has recently been discovered that combines both properties of ferro and antiferromagnetism. We study the appearance of altermagnetic phase tunable by external magnetic flux in a lattice model. Based on the behavior of the altermagnetic order parameter, spin correlations, we demonstrate the effect of magnetic flux on this exotic phase. Our investigation highlights the role of the interplay between electron correlation, magnetic flux, and lattice symmetry in stabilizing altermagnetic phases.

Long-range correlations are used to probe collective behaviour in many-body systems. In finite systems, however, global conservation of energy, momentum, particle number, and other conserved charges can itself generate correlations between otherwise independent degrees of freedom. It is therefore crucial to remove the contribution of these conservation-induced correlations from observed long-range correlations for understanding the nature of the emergent collectivity.

In this talk, I will present a unified conditional-probability framework in which equilibrium statistics and conservation-induced correlations emerge from conditioning on additive conserved quantities. The one-mode conditional law yields the Maxwell–Boltzmann, Bose–Einstein, and Fermi–Dirac distributions at leading saddle order, while the two-mode law gives the leading finite-rank covariance induced by exact conservation. This structure allows us to construct observables orthogonal to selected conserved quantities, for which the leading conservation-induced covariance vanishes. As an application, I will discuss long-range correlations in high-energy p-Pb collisions, which exhibit patterns resembling collective behaviour in collisions of large nuclei where they are commonly associated with hydrodynamic collective response. Conservation effects are particularly relevant in these smaller systems because fewer particles are produced. Using PYTHIA generated events, I will illustrate how conservation-aligned and conservation-orthogonal contributions can be separated, and discuss the implications for interpreting the emergent collective behaviour. [Based on arXiv:2606.29050]

The nature of the chiral phase transition in QCD with three massless quark flavors remained unresolved (until recently) despite being studied for nearly four decades. I will briefly introduce the mathematical framework of lattice QCD. I will present lattice QCD results on the chiral phase transition temperature, at which the spontaneously broken three-flavor chiral symmetry is expected to be restored. The methodology to study this phase transition relies heavily on the universal scaling techniques from statistical field theory. I will discuss the pseudo-critical behavior of the three-flavor QCD using highly improved staggered quarks (HISQ) on lattices with temporal extent N_\tau = 8, and for quark masses corresponding to a pseudoscalar Goldstone mass in the range 80 MeV <m_\pi <140 MeV. The findings are consistent with the occurrence of a second-order chiral phase transition in the limit of vanishing quark masses. The chiral phase transition temperature at this finite value of the lattice spacing is determined to be close to 100 MeV.

With the increasing precision of LHC measurements, reliable higher-order Standard Model predictions are becoming increasingly important for collider phenomenology. In this talk, I will discuss my work on higher-order QCD and electroweak corrections, focusing on multi-loop scattering amplitudes and Feynman integrals, using both analytical and numerical methods.

I will also discuss the numerical evaluation and interpolation of amplitudes over phase space and their efficient use within a VEGAS-based Monte Carlo integration. Finally, I will present some recent results from my work and discuss their applications to precision studies of Standard Model processes at the LHC.

Neutrino oscillation experiments reveal a definite flavour structure, but its origin remains unknown. In this talk, I present a framework combining modular S4 symmetry with the inverse seesaw mechanism, where modular forms constrain the lepton flavour structure. The framework provides a low-scale realisation of neutrino mass generation and allows the resulting flavour structure to be tested through neutrino oscillation and other low-energy observables. I then discuss resonant leptogenesis from nearly degenerate heavy neutrinos and how the observed baryon asymmetry can be generated. Finally, I discuss how this framework motivates a natural extension toward Kahler corrections and supersymmetry breaking, which forms the basis of my proposed work.

Low-energy quantum few-body systems provide an ideal framework for exploring universal phenomena that emerge from short-range interactions. Since Quantum Chromodynamics becomes non-perturbative at hadronic scales, direct calculations of low-energy nuclear observables remain challenging. Effective Field Theories (EFTs) overcome this difficulty by exploiting the separation of scales between low-energy physics and unresolved short-distance dynamics. In the regime where typical momenta are well below the pion mass, pionless EFT provides a systematic and model-independent description of few-body systems in terms of contact interactions organized by power counting and renormalization. Owing to the large scattering lengths, pionless EFT naturally captures universal behavior near the unitary limit and offers a powerful framework for studying renormalization, scale invariance and few-body correlations.

In this talk, I will discuss universal properties and structural aspects of three- and four-body quantum systems using advanced momentum- and coordinate-space few-body methods. The three-body sector is explored through a possible S-wave two-neutron halo-bound D^{0}nn system in the J^{pi}=0^{+}, T=3/2 channel. Using a leading-order (LO) Faddeev formulation with separable contact interactions within the zero-coupling limit, the system is connected to the Skornyakov-Ter-Martirosyan (STM) equations. The analysis reveals an Efimov-like renormalization-group limit-cycle behavior in the running three-body coupling, while the inclusion of a LO three-body force restores cutoff independence and renormalization-group invariance. The resulting universal halo-bound structure is characterized through root-mean-square radii, the n-D^{0}-n opening angle and matter-density distributions. Extending these ideas to four-body systems, multichannel elastic and rearrangement scattering between dimer-dimer and trimer-atom configurations of four-component fermions is studied using the configuration-space Resonating Group Method within LO pionless EFT. The results demonstrate regulator-independent scattering observables without the need for an additional four-body counter term at LO. Near threshold crossings, strong channel coupling produces enhanced rearrangement processes and large scattering lengths, indicating the presence of nearby four-body resonances and highlighting the sensitivity of low-energy four-body dynamics to the underlying few-body spectrum. Finally, higher-order four-body structural calculations are performed using newly developed variational approaches, the Two-Multiplier Method (TMM), combined with the Stochastic Variational Method. This method enable the first NLO pionless EFT prediction of the (^{4}He) point-proton rms charge radius and demonstrate the necessity of promoting a short-range four-body interaction at NLO to maintain renormalization-group invariance. Furthermore, a systematic comparison among perturbative, non-perturbative and Coulomb-free formulations shows that uncertainties associated with short-range strong interactions dominate over those arising from the long-range Coulomb interaction. This weak sensitivity to the static Coulomb contribution provides theoretical justification for simplifying the extraction of bound-state structural observables by neglecting the Coulomb interaction when the strong interaction is treated consistently up to first order in the effective range expansion.

Overall, this work establishes a unified understanding of universality from exotic three-body halo systems to four-body reaction dynamics and nuclear structure, highlighting the predictive power of low-energy EFTs combined with modern few-body techniques.

Core-collapse supernovae provide unique laboratories for new physics in the neutrino sector, where enormous neutrino densities enable both collective neutrino interactions and production of new particles. In this talk, I will discuss two complementary probes of beyond-the-Standard-Model physics in this environment. First, I will examine how nonstandard neutrino self-interactions (νNSSI) affect neutrino heating behind the stalled CCSN shock. While νNSSI may have little impact on the emergent neutrino signal, they can modify neutrino absorption, pair annihilation, and scattering processes responsible for depositing energy in the stellar mantle. Because the explosion mechanism may be sensitive to heating at the ~10% level, these effects provide a potential probe of νNSSI. I will then consider a neutrinophilic dark sector, in which dark matter couples exclusively to neutrinos through a vector mediator. The extreme neutrino densities inside the supernova neutrino sphere can lead to efficient production of such particles through neutrino annihilation, providing an additional channel for supernova cooling. Requiring consistency with the SN1987A neutrino signal yields new constraints on neutrino–dark-sector interactions, improving existing bounds by up to five orders of magnitude for dark-matter at masses below 100 MeV.

The astrophysical origin of certain proton-rich isotopes in nature has remained an open problem in nuclear astrophysics for decades. In this talk, I will discuss our recent work on the νp-process in neutrino-driven outflows. In this work, we identify the conditions under which outflow models based on modern supernova simulations can successfully reproduce the observed Solar-System abundances of the light p-nuclei, including the peculiar Mo and Ru isotopes. I will then show how these nucleosynthetic predictions become sensitive probes of neutrino flavor evolution. In particular, fast collective neutrino oscillations can dramatically enhance the production of key p-nuclides. In fact, the observed p-nuclide abundance pattern in the solar system is consistent with flavor conversion that sets in within a few kilometers of the proto-neutron star surface. These results establish an intriguing connection between the quantum dynamics of neutrino flavor and the composition of our Solar System, suggesting that the observed isotopic abundances provide indirect evidence for neutrino flavor transformations in supernovae.

I will discuss the rotational Brownian motion of heavy quarks in QCD medium and present analytical results for polarization of open heavy-flavor hadrons. Assuming that heavy quarks are initially spin polarized along the direction of magnetic field in heavy-ion collisions, I will present comparisons of our results with recent experimental data from ALICE collaboration for $D^{*+}$ meson, and also provide predictions for spin polarization of open charm baryons. I will argue that the transverse momentum dependence of heavy quark polarization may serve as a distinctive signature of the intense initial magnetic field generated in off-central relativistic heavy-ion collisions. This talk will be based on our recent publication Phys. Lett. B 873 (2026) 140202.

Neutrinos are among the lightest and the most abundant relic particles in the Universe. Neutrino physics represents a major frontier of high energy and astro-particle physics research today. A succession of seminal results from experiments involving neutrinos from a variety of sources (the sun, the atmosphere, reactors and accelerators) have established the phenomenon of neutrino flavor oscillations implying the existence of tiny non-zero neutrino masses. On the theoretical front, it is well-known that neutrinos are assumed to be massless within the Standard Model of particle physics. Therefore, the experimental observation of neutrino oscillations provides concrete evidence in favor of physics beyond the Standard Model. Due to this reason neutrinos have been an intensive area of research in the past several decades. Focusing our attention on the key experimental results from neutrino physics, this talk will discuss the physics potential of next generation neutrino experiments such as DUNE.

The remarkable agreement between the observed light-element abundances and the predictions of big bang nucleosynthesis (BBN) makes BBN a powerful probe of physics beyond the Standard Model (BSM). In this talk, I will present the BBN constraints on a specific BSM particle, the Majoron, and discuss its cosmological implications. I will also highlight the caveats of the standard BBN scenario in light of the long-standing cosmological lithium problem and briefly outline a possible solution.

In naturally occurring Feldspar crystals used in thermoluminescence (TL) dating there are numerous impurity states in the energy gap below the conduction band. Electrons got trapped in these impurity (metastable) states. However, they may quantum mechanically tunnel from the trap centers to another and can recombine in the recombination centers causing a fading of the TL signal. This fading affects the age determination. The model which is used by the TL community to correct this age is that of the Huntley's (D.J. Huntley, 2001). We argue that the Huntley model oversimplify the mechanism of fading thus gives less accurate age determination. We give a new model based on diffusion, and compare the predictions of the model with the data. We notice that our model gives more accurate determination of the age.

Over the recent years, the research on the moire structures by stacking of 2D monolayers with interlayer twisting have gained appreciable attention after the discovery of unconventional superconductivity and the correlated insulating phase in the twisted bilayer graphene. Beyond twisted bilayer graphene, other twisted 2D homo- and heterostructures have exhibited diverse emergent, exotic quantum phenomena such as ferromagnetism, topological phenomena, quantum Hall effects, Mott insulating behavior, etc. These results have motivated us to investigate the quantum phenomena further and underscores the potential of the moire heterostructures for next-generation applications.

In this work, we have theoretically investigated the Gr/hBN heterostructures - how stacking configurations, interlayer interactions, interlayer twisting, and the external parameters such as electric fields influence their electronic and topological behaviour. At first, we introduced the twistronics of 2D monolayers, moire heterostructures and motivation for my research work along with the employed theoretical methods. Then we began with our work as follows - the effect of interfacial configurations on vdW interactions and the electronic transport properties of Gr/hBN heterostructures. After that, the investigations of twist-angle and electric field driven electronic structures and topological phase transitions using Berry curvature and Chern number calculations in Gr/hBN moire heterostructures. Then, the electronic properties and switching between the topological phases as a function of twist angle in a double-moire hBN/Gr/hBN heterostructure. At last, we summarize the results on the Gr/hBN moire heterostructures, and outline the future
research directions of the 2D moire heterostructures.

We investigate the HL-LHC phenomenology of a heavy vectorlike fermionic portal matter (PM) that mixes with the Standard Model third-generation up-type quark and decays predominantly into a top quark and a dark photon. We focus on the long-lived dark photon scenario, in which the dark photon travels a macroscopic distance before decaying hadronically inside the detector, giving rise to displaced dark photon jets. To identify these signatures, we develop a machine-learning-based tagging strategy using a boosted decision tree trained on displaced-vertex and jet-substructure observables reconstructed from Delphes detector simulations. Boosted top quarks are identified using the Johns Hopkins top tagger. We consider two complementary event topologies containing one displaced dark photon jet and one boosted top quark $(\gamma_d+t)$, and at least two displaced dark photon jets together with at least one boosted top quark $(\geq2,\gamma_d+\geq1,t)$. In addition, reconstruction of the top--dark-photon invariant mass provides further discrimination between signal and background. We evaluate the sensitivity of this search strategy to the portal matter mass and dark photon proper decay length at the HL-LHC with a center-of-mass energy of 14 TeV and an integrated luminosity of 3 ab$^{-1}$. Our results indicate that displaced dark photon jet signatures provide a complementary avenue for exploring fermionic portal matter scenarios at the HL-LHC.

Graphene nanoribbons (GNRs) are quasi-one-dimensional quantum systems that exhibit rich electronic and spintronic properties arising from quantum confinement, edge geometry, and external perturbations. This talk presents a systematic theoretical study of quantum transport in armchair (AGNR) and zigzag (ZGNR) graphene nanoribbons using a tight-binding model combined with the Non-Equilibrium Green's Function (NEGF) formalism, solved self-consistently with the Poisson equation.

The role of quantum confinement, magnetic fields, and spatially varying electric fields in tailoring the electronic properties of graphene nanoribbons is discussed. Particular emphasis is given to spin-dependent transport induced by Rashba spin-orbit coupling and the emergence of spin-polarized states in zigzag graphene nanoribbons. The influence of various dephasing mechanisms including phase, momentum, and spin relaxation processes on transport characteristics and local electronic structure is also presented. Finally, results on Berry curvature and anomalous Hall conductivity in monolayer graphene with Rashba spin-orbit coupling are presented, revealing non-trivial topological signatures driven by spin-momentum locking. The results demonstrate the versatility of graphene nanoribbons as tunable quantum platforms and illustrate the effectiveness of the NEGF approach for studying non-equilibrium transport in nanoscale systems.

We investigate the role of electronic interactions in a two-dimensional generalized Su–Schrieffer–Heeger (SSH) model using an unrestricted Hartree–Fock mean-field approach. Depending on the hopping parameters, the noninteracting system hosts either Dirac points or quadratic band touchings, providing a rich platform to study interaction-driven instabilities. Our analysis reveals a diverse phase diagram containing several competing ordered phases, including a quantum anomalous Hall phase, stripe charge-ordered states, a site-nematic insulating phase, and a bond-nematic Dirac semimetal (BNDS). In particular, we demonstrate the emergence of the BNDS phase, characterized by spontaneous rotational symmetry breaking while preserving gapless Dirac excitations, in agreement with recent tensor-network and density-matrix renormalization-group studies. We further show that tuning hopping anisotropy and staggered sublattice potentials strongly influences the competition among these phases and can stabilize distinct correlated topological states. Our results highlight how interactions and lattice geometry together can generate unconventional symmetry-broken and topological phases in two-dimensional systems, providing useful insights for future realizations in engineered quantum materials and optical lattice platforms.

Motivated by many contemporary problems in condensed matter physics where matter particles experience random gauge fields, we investigate the physics of fermions on a square lattice with pi-flux (that realizes Dirac fermions at low energies), subjected to flux disorder arising from a random Z2 gauge field that results from the presence of flux defects (plaquettes with zero flux). At half-filling, where the system possesses BDI symmetry, we show that a new class of critical phases is realized, with the states at zero energy showing a multifractal character. The multifractal properties depend on the concentration c of the π-flux defects and spatial correlations between the flux defects. These states are characterized by the singularity spectrum, Lyapunov exponents, and transport properties. For any concentration of flux defects, we find that the multi-fractal spectrum shows termination, but not freezing. We characterize this class of critical states by uncovering a relation between the conductivity and the Lyapunov exponent, which is satisfied by the states irrespective of the concentration or the local correlations between the flux defects. We demonstrate that renormalization group methods, based on perturbing the Dirac point, fail to capture this new class of critical states. This work not only offers new challenges to theory, but is also likely to be useful in understanding a variety of problems where fermions interact with discrete gauge fields. Ref: Critical States of Fermions with Z2 Flux Disorder. Hiranmay Das, Naba P. Nayak, Soumya Bera, and Vijay B. Shenoy. https://doi.org/10.1103/wsqw-2xh4

Ultracold atomic gases have emerged as one of the most versatile platforms for exploring fundamental phenomena across diverse areas of physics, ranging from classical fluid dynamics to strongly correlated condensed matter systems. The remarkable tunability of interactions, dimensionality, and geometry--together with the availability of multiple atomic species that can undergo Bose–Einstein condensation (BEC)--enables the realization of a wide variety of exotic quantum phases, including supersolids and engineered lattice Hamiltonians relevant to condensed matter physics.

In this talk, I will begin with a brief overview of ultracold quantum matter, particularly its relevance in modern quantum technology. Then, I will highlight recent developments in realizing supersolid states of matter in BECs of magnetic lanthanide atoms, emphasizing how a supersolid in ring-shaped geometry provides a very clean platform for the investigation of collective excitations, such as Higgs-like amplitude modes. I will then present how one can leverage the dispersion relation of Higgs amplitude modes to create and detect massive Higgs quasiparticles in an experimentally feasible scenario.

We study the electron transport in mesoscopic systems using two different setups. First we study charge and spin transport across a junction between altermagnet (AM) and

In this talk, we will discuss searches for dark matter (DM) across a broad mass range, spanning from the MeV to PeV scales. We will first quantify the neutrino-background-limited regime relevant to sub-GeV DM searches through the Migdal effect. We will then turn to higher masses and show how observations from IceCube and LHAASO are opening new windows into previously unexplored regions of the DM parameter space, particularly for DM–electron interactions and for heavy decaying DM, respectively.

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.

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.

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.

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 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.

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

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.

The Standard Model of particle physics is one of the most successful theories for describing fundamental particle interactions, yet it remains incomplete, failing to explain phenomena such as dark matter, the matter-antimatter asymmetry in the universe, and CP violation, among others. This has motivated the exploration of physics beyond the Standard Model (BSM).

Neutrino oscillations represent a key phenomenon in BSM physics, providing the first clear evidence of physics beyond the Standard Model. In this work, I review past experiments that have contributed to the detection of neutrinos and the precise measurement of their oscillation parameters.

The Deep Underground Neutrino Experiment (DUNE) is a next-generation long-baseline neutrino oscillation experiment. Its primary goals include the precise measurement of CP violation in the neutrino sector, determination of the neutrino mass ordering, and searches for new physics.

A particular focus of this study is the detection of tau neutrinos—the least studied of the three neutrino flavors—at DUNE. I will discuss the associated challenges, including the identification of short-lived tau leptons produced in charged-current tau neutrino interactions amid high backgrounds. Finally, I explore the role of machine learning techniques in overcoming these challenges to improve tau neutrino event reconstruction, classification, and signal extraction.

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.

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.

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.

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

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.

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.

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.