arXiv subjects

Gurudatt Gaur

Publications and source records attributed to Gurudatt Gaur.

8 recordsLinked to original sources

arXiv2026

Finite-Momentum Kinetic Corrections to Viscous Tensor Perturbations in an Expanding Universe

We study tensor perturbations propagating through a viscous relativistic medium in a spatially flat FLRW universe, with particular emphasis on the correction produced by spatial free streaming beyond a local causal relaxation model. We start from the relaxation-time Boltzmann equation used by Baym, Patil, and Pethick to describe the response of matter to a gravitational wave. In the zero-streaming limit, the tensor stress obeys a Maxwell-Cattaneo, or linear Muller-Israel-Stewart, relation. We then retain the spatial streaming term and evaluate the resulting angular response analytically for an ultrarelativistic isotropic medium. The resulting kinetic response is coupled to the tensor Einstein equation and solved numerically in a flat matter-plus-Lambda background, with comparison to the local MIS propagation model and an independent kinetic WKB calculation. For the illustrative normalization considered, the full numerical calculation produces a nonmonotonic correction to the tensor power transfer function, with a maximum of about 0.8 percent near x equal to 0.37 and a minimum of about minus 5.6 percent near x equal to 1.97. These features are stable under angular-resolution and ODE-tolerance tests and are reproduced by the kinetic WKB calculation. We also find a corresponding finite-momentum phase correction. The effect is a property of the specified single-relaxation-time kinetic model and should not be interpreted as a universal transport law.

gr-qc↗

arXiv2026

Gravitational Sedimentation and Rebound of Strongly Coupled Dusty Plasma Crystals: A Molecular Dynamics Study

The gravitational sedimentation of strongly coupled dusty plasma crystals is investigated using molecular dynamics simulations. Initially, the dust particles are levitated by the balance between the upward external electric field and gravity. Sedimentation is initiated by removing the electric field, allowing the particles to settle collectively under gravity while interacting through the Yukawa (screened Coulomb) potential. Single-layer, AB-stacked bilayer, and ABA-stacked trilayer crystals are investigated to examine the influence of crystal geometry on the sedimentation dynamics. All crystal configurations undergo collective gravitational settling while preserving their in-plane hexagonal ordering during the initial stages of sedimentation. Upon collision with a reflecting boundary, the multilayer crystals undergo transient interlayer compression followed by sequential momentum transfer between neighboring layers, producing coherent collective rebound. In particular, the trilayer exhibits sequential layer-by-layer momentum propagation from the lower to the middle and finally to the upper layer. During successive sedimentation--rebound cycles, repeated interlayer interactions progressively degrade the initial ABA stacking while preserving the collective mechanical response of the crystal. These results demonstrate that strong Yukawa coupling enables multilayer dusty plasma crystals to sustain repeated impacts while maintaining coherent collective motion despite gradual structural evolution. The present study provides a particle-resolved description of gravitational sedimentation in multilayer dusty plasma crystals and offers a theoretical framework for interpreting laboratory experiments following the removal of electrostatic confinement.

physics.plasm-ph↗

arXiv2026

Tearing and Kelvin-Helmholtz dynamics in fully kinetic particle-in-cell simulations of electron-scale current sheets

We investigate the stability and nonlinear evolution of localized electron-scale current sheets using fully kinetic, electromagnetic particle-in-cell (PIC) simulations in two and three dimensions. By varying the current-sheet thickness, we examine how it influences the dominant instability and subsequent nonlinear dynamics. In two dimensions, the evolution is governed by electron inertial tearing, with growth rates in good agreement with linear electron magnetohydrodynamics (EMHD) predictions. In three dimensions, however, a thickness-dependent transition emerges. For wider current sheets, a velocity-shear-driven Kelvin-Helmholtz-type instability dominates the early and intermediate evolution, leading to vortex formation and strong modulation of the current layer, followed by the re-emergence of tearing at later times. In contrast, thinner sheets remain tearing-dominated throughout, with no transition to a shear-driven regime, although their effective growth rate is reduced relative to linear predictions, suggesting the influence of mode coupling and three-dimensional effects. These results establish a thickness-dependent transition from tearing-dominated to shear-driven dynamics and reveal a nonlinear sequence of instability evolution in fully kinetic systems, providing new insight into the competition between curvature-driven and shear-driven instabilities in electron-scale current sheets.

physics.plasm-ph↗

arXiv2025

Investigating the Kinetic Effects on Current Gradient-Driven Instabilities of Electron Current Layers via Particle-in-Cell Simulations

Electron current layers, which form in various natural and laboratory plasmas, are susceptible to multiple instabilities, with tearing being a prominent instability driven by current gradients. Tearing is considered a potential mechanism for magnetic reconnection in collisionless regimes, where electron inertia acts as a non-ideal factor that causes magnetic field lines to break and reconnect. In contrast, another mode, known as the surface-preserving mode, also driven by current gradients, maintains the magnetic field topology. In this study, we investigate the kinetic effects on these modes in the presence of finite electron temperatures using two-dimensional particle-in-cell simulations. Our findings reveal that temperature significantly stabilizes the tearing mode, particularly at higher temperatures, due to an increased electron Larmor radius and the associated magnetic field diffusion. We also examine the interplay between the guide field and temperature. Additionally, we observe that growth rates for the surface-preserving mode, in contrast to the tearing mode, increase with temperature, likely due to enhanced electron flow velocities. Furthermore, we identify cases with mixed modes, where both tearing and surface-preserving modes coexist, exhibiting asymmetric structures characteristic of asymmetric magnetic reconnection. Finally, we outline potential future research directions that build upon our findings.

physics.plasm-ph↗

arXiv2024

Detection of Gravitational Wave Signals from Precessing Binary Black Hole Systems using Convolutional Neural Network

Current searches for gravitational waves (GWs) from black hole binaries using the LIGO and Virgo observatories are limited to analytical models for systems with black hole spins aligned (or anti-aligned) with the orbital angular momentum of the binary. Detecting black hole binaries with precessing spinsis crucial for gaining unique astrophysical insights into the formation of these sources. Therefore, it is essential to develop a search strategy capable of identifying compact binaries with precessing spins. Aligned-spin waveform models are inadequate for detecting compact binaries with high precessing spins. While several efforts have been made to construct template banks for detecting precessing binaries using matched filtering, this approach requires many templates to cover the entire search parameter space, significantly increasing the computational cost. This work explores the detection of GW signals from binary black holes(BBH) with both aligned and precessing spins using a convolutional neural network (CNN). We frame the detection of GW signals from aligned or precessing BBH systems as a hierarchical binary classification problem. The first CNN model classifies strain data as either pure noise or noisy signals (GWs from BBH). A second CNN model then classifies the detected noisy signal data as originating from either precessing or non-precessing (aligned/anti-aligned) systems. Using simulated data, the trained classifier distinguishes between noise and noisy GW signals with more than 99% accuracy. The second classifier further differentiates between aligned and highly precessing signals with around 95% accuracy. We extended our analysis to a multi-detector framework by performing a coincident test. Additionally, we tested the performance of our trained architecture on data from the first three observation runs of LIGO to identify detected BBH events as either aligned or precessing.

gr-qc↗

arXiv2021

The Science Case for LIGO-India

The global network of gravitational-wave detectors has completed three observing runs with $\sim 50$ detections of merging compact binaries. A third LIGO detector, with comparable astrophysical reach, is to be built in India (LIGO-Aundha) and expected to be operational during the latter part of this decade. Multiple detectors operating at different parts of the globe will provide several pairs of interferometers with longer baselines and an increased network SNR. This will improve the sky localisation of GW events. Multiple detectors simultaneously in operation will also increase the baseline duty factor, thereby, leading to an improvement in the detection rates and, hence, the completeness of surveys. In this paper, we quantify the improvements due to the expansion of the LIGO Global Network (LGN) in the precision with which source properties will be measured. We also present examples of how this expansion will give a boost to tests of fundamental physics.

gr-qc↗

arXiv2021

Employing Deep Learning for Detection of Gravitational Waves from Compact Binary Coalescences

The matched filtering paradigm is the mainstay of gravitational wave (GW) searches from astrophysical coalescing compact binaries. The compact binary coalescence (CBC) search pipelines perform the matched filter between the GW detector's data and a large set of analytical waveforms. However, the computational cost of performing matched filter is very high as the required number of the analytical waveforms is also high. Recently, various deep learning-based methods have been deployed to identify a GW signal in the detector output as an alternative to computationally expensive matched filtering techniques. In past work, the researchers have considered the detection of GW signal mainly as a classification problem, in which they train the deep learning-based architecture by considering the noise and the GW signal as two different classes. However, in this work, for the first time, we have combined the Convolutional Neural Network (CNN) and matched filter methods to reduce the computational cost of the search by reducing the number of matched filtering operations. We have implemented the CNN based architecture not only for classification of the signal but also to identify the location of the signal in the intrinsic parameter space. Identifying the location in which the detected signal lies enables us to perform the matched filter operations between the data and the analytical waveforms generated for the smaller region of the parameter space only - thereby reducing the computational cost of the search. We demonstrate our method for two-dimensional parameter space for stellar to high mass binary black hole systems. In particular, we are able to classify between pure noise and noisy BBH signals with 99% accuracy. Further, the detected signals have been sub-classified into patches in mass components with an average accuracy > 97%

gr-qc↗

arXiv2015

Tearing and Surface Preserving Electron Magnetohydrodynamic Modes in A Current Layer

In this paper, we have carried out linear and nonlinear analysis of tearing and surface preserving modes of two dimensional (2D) Electron Magnetohydrodynamics (EMHD). A linear analysis shows that the perturbations parallel to equilibrium magnetic field $B_0$ (characteristic tangent hyperbolic spatial profile), driven by the current gradients, lead to two different modes. The first mode is the tearing mode having a non-local behavior which requires the null-line in the magnetic field profile. Whereas, the second mode is a surface preserving local mode which does not require the null-line in the magnetic field. The quantity $B_0 - B_0^{''}$ should change sign for these modes to exist. In nonlinear simulations, for tearing case we observe formation of magnetic island at the null-line due to the reconnection of magnetic field lines. However, for surface preserving mode, a channel like structure is observed instead of the island structure.

physics.plasm-ph↗