arXiv subjects

Gunindra Krishna Mahanta

Publications and source records attributed to Gunindra Krishna Mahanta.

4 recordsLinked to original sources

arXiv2026

Conventional vs. modified GTD metrics: Survival of modified GTD metrics in AdS spacetime and thermodynamic ensembles

Thermodynamic geometry provides a powerful framework for probing the microscopic structure of thermodynamic systems. Among its formulations, Geometrothermodynamics (GTD) has been widely applied to black hole thermodynamics, owing to its Legendre-invariant construction. However, recent work has shown that conventional GTD metrics fail to encode essential physical boundaries of thermodynamic phase space. By modifying the conventional metric structure, three new GTD metrics were previously introduced, which successfully capture these boundaries in regular spacetime. Whether such modified metrics remain viable in different spacetime backgrounds and under changes of thermodynamic ensemble has remained an open question. In this work, I address this issue by investigating the behavior of modified GTD metrics in AdS spacetime and across different thermodynamic ensembles in the framework of Bardeen AdS black hole. An analysis of thermodynamic geodesics demonstrates that the modified GTD metrics consistently respect physical boundaries of the phase space, in contrast to conventional GTD metrics. This behavior is preserved in AdS spacetime and under Legendre transformations, establishing the robustness and universality of the modified GTD framework.

gr-qc↗

arXiv2026

Particle acceleration to PeV energies in Pulsar Wind Nebula: a two zone model

\textit{PeVatrons} are the extreme galactic accelerators capable of producing PeV particles. Recent observation of Large High Altitude Air Shower Observatory have detected UHE photons ($\geq$ 100 TeV) from 43 galactic sources. Detection of UHE photons demands the presence of at least PeV particles in the acceleration site. Although the exact nature of most of the sources are still unknown, a large fraction of these sources have spatial association with pulsar wind nebula. In this work we investigate the acceleration mechanism in pulsar wind nebula by following a magnetohydrodynamics approach. Current study relates the MHD flow solution in immediate downstream with the particle spectrum and spectral energy distribution of photons. Our study shows that MHD description in the PWN environment reduces the parameter space and most of the parameters can be constrained in terms of a single parameter, \textit{the magnetization parameter} $σ$ only. Considering the effect of $σ$, we show that in low $σ$ environment pulsar wind nebula can produce PeV particles. We have also investigate the role of turbulence in the nebular region in acceleration of particle to PeV energy. Current study shows that both low $σ$ environment and turbulence environment is favorable for acceleration of particles up to PeV energy. We have also tested our model in two different LHAASO detected PeVatron 1LHAASO J1848-000u and 1LHAASO J1929+1846u.

astro-ph.HE↗

arXiv2025

Thermodynamic Geodesics in Bardeen Regular Black Hole: Conventional vs. Modified Geometrothermodynamics Metrics

Thermodynamic geometry allow us to study the microscopic behavior of black hole system by defining a metric structure in thermodynamic phase space. Among the various thermodynamic metric structures, metrics defined by geometrothermodynamics (GTD) are extensively used to study the various thermodynamic system due to its Legendre invariant nature. In this work we investigate the behavior of thermodynamic geodesic of Bardeen regular black hole in thermodynamic space defined by three different GTD metrics. Based on the behavior of thermodynamic geodesic as well as thermodynamic curvature we argued that conventional GTD metric need some modifications to reflect all the thermodynamical properties of a system. We also modified the conventional GTD metrics and explore the behavior of thermodynamic geodesic defined by the modified metrics. Our study shows that the modified GTD metrics contain most of the information about the thermodynamical boundaries such as temperature vanishing line, spinodal line etc. of a black hole system. Based on the property of geodesic and Ricci scalar defined by the modified metrics we argued that the modified version of GTD metric are most suitable metric structures for studying the underlying thermodynamic behavior of a black hole system.

gr-qc↗

arXiv2024

uGMRT observation of the unidentified PeVatron candidate LHAASO J2108+5157

Recent observations by the Large High Altitude Air Shower Observatory (LHAASO) detected Ultra High Energy (UHE) photons in the range 100 TeV to 1.4 PeV from twelve sources including Crab nebula. The detection of these photons demands the presence of at least PeV energy particle in the source. It is important to understand particle acceleration and radiation emission processes in such source. One of those twelve sources, LHAASO J2108+5157 does not show any association or counterparts at any other wavelength. In search of counterpart, we surveyed the region with Giant Metrewave Radio Telescope (GMRT) at 650 MHz frequency. GMRT observation revel radio emission from an extended source within the PSF of LHAASO which shows disk-jet morphology. Considering the spatial association and extent of the source, it is plausible that particle acceleration to PeV energies originates from this source.

astro-ph.HE↗