Title : Propagation of Solar Energetic Particles in the Heliosphere

Abstract

Solar Energetic Particles (SEPs) are charged particles with energies ranging from keV to several GeV, accelerated during solar flares and CMEs. Understanding SEPs is crucial for space weather. These particles generally follow the large-scale interplanetary magnetic field, however, heliospheric magnetic turbulence repeatedly scatters them. This scattering governs SEP propagation, and diffusion parameters such as the parallel diffusion coefficient quantify the strength of diffusion along magnetic field lines. By combining X-ray spectral observations from the Solar X-ray Monitor (XSM) onboard Chandrayaan-2 with particle flux measurements from multiple spacecraft, and by modelling the particle propagation event, we experimentally determine the SEP diffusion coefficient.

Title : What controls the oxygen isotope–salinity relation in the northern Indian Ocean?

Abstract

Seawater oxygen isotopic composition (δ18O) and salinity show a near-linear covariance, forming the basis of widely used δ18O–S relationships. These relationships are often applied to reconstruct past salinity in the ocean from foraminiferal δ18O, yet the associated uncertainties can be large, with errors in inferred salinity reaching >50%. Much of this uncertainty stems from the limited availability of high-quality modern seawater δ18O measurements and an incomplete understanding of the processes that shape this relationship. In this talk, I will present a comprehensive modern seawater δ18O dataset generated at PRL, and discuss how it advances our understanding of the controls governing the δ18O–salinity relationship in the northern Indian Ocean.

Title : Quasiclassical electron transport in topological Weyl semimetals

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.

Title : Monte Carlo Sampling for Wave Functions Requiring (Anti)Symmetrization

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 : Random encounters in asteroseismology and their impact on a scientific career

Abstract

As a little boy, I was already fascinated by the magnificent light show of the twinkling stars in the night sky. My scientific career started almost 30 years ago when, as a physics student at KU Leuven (Belgium), I prepared my master's thesis under the supervision of Conny Aerts. Thanks to her enthusiasm, I started to look into asteroseismology, where the stars reveal the secrets of their hidden interior through the way they vibrate. In this presentation I would like to demonstrate how my interest in stellar pulsations in combination with a few random encounters have led to the two projects that I consider my greatest scientific achievements to date, namely the close collaboration with colleagues from both China (via the LAMOST-Kepler project) and India (via the BINA project). The strength of these projects will be demonstrated by some scientific results in different domains.

Title : Long term X-ray Spectral study of Seyfert Galaxy Mrk 530

Abstract

Active Galactic Nuclei (AGN) are among the most luminous astronomical sources, powered by accretion of matter onto a Supermassive Black Hole (SMBH). Their X-ray emission arises from the upscattering of optical/UV photons from the accretion disk by a hot corona of relativistic electrons, producing a power-law spectrum, which is modified by absorption and reflection features. In some AGN, an excess of photons above the standard power-law can be observed below the 2 keV energy range, termed as Soft Excess. The origin of this Soft excess is still a matter of debate, and various theories have been proposed to explain this excess emission. The warm corona model attributes this emission to arise from the inverse Comptonizaton of the disk photons in an optically thick, warm (0.1 - 1 keV) corona. Alternatively, the blurred ionized reflection scenario explains the soft excess to be a result of the relativistic blurring of the reprocessed emission from the disk due to the effects of strong gravity near the SMBH. More recently, hybrid models combining both warm Comptonization and ionized reflection components have also been proposed.

Title : Supercurrent detection of Majorana-mediated quantum-phase transitions

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 : Seasonal Variability of Water Vapor Dynamics in the Semi-Arid Region of Western India - revelations from isotopic investigation at Mt. Abu, Rajasthan.

Abstract

This study presents the first continuous year-long measurement of stable isotopes (d18O, dD, and d-excess) in atmospheric water vapor over semi-arid western India. Continuous in-situ observations captured isotopic variations from daily to seasonal scales to identify key controlling processes. Temporal changes in vapor isotopes are governed by shifts in moisture sources and the influence of recycled moisture, producing a distinct seasonal isotopic baseline. A pronounced isotopic depletion precedes rainfall events by several days, suggesting its potential as a precursor to precipitation. A sharp isotopic transition observed in late April indicates a major shift in vapor source. The dominant moisture sources—northern and southern Arabian Sea, arid terrestrial regions of Iraq–Iran–Afghanistan–Pakistan, and the wetter eastern landmass of India and the Bay of Bengal—each impart distinct isotopic characteristics, enabling the identification of seasonal vapor origins and their hydrometeorological implications.

Title : Different Ways to Calculate NLP Amplitudes of Scattering Processes

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 : Broad-band temporal and spectral study of Blazars

Abstract

Blazars are the most powerful subclass of active galactic nuclei in which observed emissions are highly Doppler boosted and observable across the entire accessible electromagnetic spectrum ranging from radio to gamma-rays, with diverse variability timescales spanning across minutes to years. The AGN activity level appears to vary on various time-scales. To date, most of the studies have focused mainly on high activity episodes, thereby offering a limited view of the source physical conditions. In our recent work we studied long-term broadband temporal and spectral study of a TeV BL Lac object TXS 0518+211 using 16 years of simultaneous optical, UV, and X-ray observations. In this blazar we find the complex nature of jet-dominated emission processes and suggest for more than one emission zone contributing to the observed broadband spectral energy distribution (SED). In this talk, I shall also present the results based on the photometric and spectroscopic observations acquired from Mt. Abu telescopes.

Title : Nitrogen fluxes and primary productivity in Archaean Ocean

Abstract

The most oxidised form of nitrogen - Nitrate (NO3⁻) - serves as an essential and often limiting nutrient for life in the modern well-oxygenated ocean. However, ~3 billion years ago (Archean eon) the Earth’s surface environment and oceans were largely deprived of oxygen. Nitrogen isotopic composition (δ¹⁵N) of sedimentary rocks of that time suggests ammonium (NH4+) dependent anaerobic nitrogen cycling. In an attempt to quantify nitrogen fluxes and productivity in such ammonium-based ecosystem, we have developed a numerical two-box model that simulates Archean nitrogen cycling under ammonium-dependent conditions. In this seminar I will be discussing the results of the model and evaluate the Archean nitrogen isotopic record.

Title : Neutrino oscillations in the plane wave and wave packet formulations

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.