Theoretical Physics Seminar
Title : Neutrino oscillations in the plane wave and wave packet formulations
Date : 04-11-2025
Time : 02:30:00
Speaker : Safana P Shaji
Area : Theoretical Physics
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.
Title : Different Ways to Calculate NLP Amplitudes of Scattering Processes
Date : 11-11-2025
Time : 02:30:00
Speaker : Shuvendu Roy, PRL
Area : Theoretical Physics
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.
Title : Supercurrent detection of Majorana-mediated quantum-phase transitions
Date : 13-11-2025
Time : 02:30:00
Speaker : Dr. Debika Debnath, PRL
Area : Theoretical Physics
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 ($\zeta, \theta$) 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)."
Title : Monte Carlo Sampling for Wave Functions Requiring (Anti)Symmetrization
Date : 18-11-2025
Time : 02:30:00
Speaker : Dr. Ajit C. Balram
Area : Theoretical Physics
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). "
Title : Quasiclassical electron transport in topological Weyl semimetals
Date : 20-11-2025
Time : 02:30:00
Speaker : Azaz Ahmad
Area : Theoretical Physics
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.