arXiv subjects

K. M. Ajith

Publications and source records attributed to K. M. Ajith.

10 recordsLinked to original sources

arXiv2025

Thermodynamics, photon sphere and thermodynamic geometry of Ayón-Beato-García Spacetime

We study the thermodynamics of the Ayón-Beato-García black hole and the relationship between photon orbits and the thermodynamic phase transitions of the black hole in AdS spacetime. We then examine the interactions between the microstructures of the black hole using Ruppeiner geometry. The radius of the photon orbit and the minimum impact parameter behave non-monotonically below the critical point, mimicking the behaviour of Hawking temperature and pressure in extended thermodynamics. Their changes during the large black hole--small black hole phase transition serve as the order parameter, possessing a critical exponent of $1/2$. The results demonstrate that the gravity and thermodynamics of the Ayón-Beato-García black hole are closely related. Furthermore, we explore the thermodynamic geometry, which provides insight into the microstructure interactions of the black hole. We find that the large black hole phase is analogous to a bosonic gas with a dominant attractive interaction, while the small black hole phase behaves like an anyonic gas with both attractive and repulsive interactions.

gr-qc↗

arXiv2025

Spinning LQG black hole as a particle accelerator

We demonstrate that the spinning LQG black hole can act as a cosmic particle accelerator. The LQG solution is singularity-free and can possess spin greater than that of a Kerr black hole. The additional black hole hair, arising from quantum effects, significantly influences the particle dynamics around the black hole. Under suitable physical conditions, the center-of-mass energy can grow arbitrarily high during the collision of two generic particles in the spacetime of an extremal black hole. In the non-extremal case, there exists a finite upper bound on the center-of-mass energy, the maximum value of which depends on the LQG parameter. These results are particularly interesting from an astrophysical perspective, especially in the context of probing Planck-scale physics.

gr-qc↗

arXiv2025

Greybody factor for an electrically charged regular-de Sitter black holes in $d$-dimensions

We investigate the propagation of scalar fields in the gravitational background of higher-dimensional, electrically charged, regular de Sitter black holes. Using an approximate analytical approach, we derive expressions for the greybody factor for both minimally and non-minimally coupled scalar fields. In the low-energy regime, we find that the greybody factor remains non-zero for minimal coupling but vanishes for non-minimal coupling, indicating a significant influence of curvature coupling on the emission profile. Examining the greybody factor alongside the effective potential, we explore how particle parameters (the angular momentum number and the non-minimal coupling constant) and spacetime parameters (the dimension, the cosmological constant, and the non-linear charge parameter) affect particle emission. While non-minimal coupling and higher angular momentum modes generally suppress the greybody factor, the non-linear charge parameter enhances it. We then compute the Hawking radiation spectra for these black holes and observe that, despite the non-linear charge enhancing the greybody factor, both non-minimal coupling and the non-linear charge ultimately reduce the total energy emission rate. These results provide insights into how modifications to classical black hole solutions in higher dimensions, through the inclusion of non-linear electrodynamics, impact their quantum emission properties.

gr-qc↗

arXiv2025

Euclidean Thermodynamics and Lyapunov Exponents of Einstein-Power-Yang-Mills AdS Black Holes

We study the thermodynamics of Einstein-Power-Yang-Mills AdS black holes via the Euclidean path integral method, incorporating appropriate boundary and counterterms. By analyzing unstable timelike and null circular geodesics, we demonstrate that their Lyapunov exponents reflect the thermodynamic phase structure obtained from the Euclidean action. Specifically, the small-large black hole phase transition, analogous to a van der Waals fluid, is signaled by a discontinuity in the Lyapunov exponent. Treating this discontinuity as an order parameter, we observe a universal critical exponent of $1/2$, consistent with mean-field theory. These results extend previous insights from black hole spacetimes with Abelian charges to scenarios involving nonlinear, non-Abelian gauge fields, highlighting the interplay between black hole thermodynamics and chaotic dynamics.

gr-qc↗

arXiv2024

Perturbations of Black Holes Surrounded by Anisotropic Matter Field

Our research aims to probe the anisotropic matter field around black holes using black hole perturbation theory. Black holes in the universe are usually surrounded by matter or fields, and it is important to study the perturbation and the characteristic modes of a black hole that coexists with such a matter field. In this study, we focus on a family of black hole solutions to Einstein's equations that extend the Reissner-Nordström spacetime to include an anisotropic matter field. In addition to mass and charge, this type of black hole possesses additional hair due to the negative radial pressure of the anisotropic matter. We investigate the perturbations of the massless scalar and electromagnetic fields and calculate the quasinormal modes (QNMs). We also study the critical orbits around the black hole and their properties to investigate the connection between the eikonal QNMs, black hole shadow radius, and Lyapunov exponent. Additionally, we analyze the grey-body factors and scattering coefficients using the perturbation results. Our findings indicate that the presence of anisotropic matter fields leads to a splitting in the QNM frequencies compared to the Schwarzschild case. This splitting feature is also reflected in the shadow radius, Lyapunov exponent, and grey-body factors.

gr-qc↗

arXiv2021

Effect of Dark Energy in Geometrothermodynamics and Phase Transitions of Regular Bardeen AdS Black Hole

We investigate thermodynamics and geometrothermodynamics of regular Bardeen AdS black hole with quintessence. The thermodynamics of the black hole is studied using temperature-entropy ($T-S$) , Pressure-Volume ($P-v$), and Gibbs energy plots, which indicate a critical behaviour.This is also confirmed from the divergence of specific heat against entropy, which shows a second-order phase transition. Moreover, we observe that the quintessence state parameter $ω$ shifts the transition point to lower entropy values. Using the concept of thermodynamic Ruppeiner and Weinhold geometry, we calculated the thermodynamic curvature scalar $R_R$ and $R_W$ in the quintessence dark energy regime ($ω=-2/3$). While these curvature scalars enable us to identify the critical behavior, they do not show divergence at the phase transition points observed in specific heat studies. To resolve this puzzle, we have adopted the method of geometrothermodynamics proposed by Hernando Quevedo. Choosing a Legendre invariant Quevedo metric, the curvature scalar $R_Q$ shows singularity at the same point as seen in the specific heat divergence.

gr-qc↗

arXiv2021

Dynamics and kinetics of phase transition for regular AdS black holes in general relativity coupled to non-linear electrodynamics

Employing the free energy landscape, we study the phase transition and its dynamics for a class of regular black holes in Anti-de Sitter spacetime governed by the coupling of non-linear electrodynamics, which reduces to Hayward and Bardeen solutions for particular values of spacetime parameters. The Fokker-Planck equation is solved numerically by imposing the reflecting boundary condition and a suitable initial condition, using which, we investigate the probabilistic evolution of regular AdS black holes. In this approach, the on-shell Gibbs free energy is treated as a function of the radius of the event horizon, which happens to be the order parameter of the phase transition. The numerical solution is also obtained for the absorbing boundary condition. The dynamics of switching between the coexistence small black hole phase and large black hole phase due to the thermal fluctuation is probed by calculating the first passage time. The effect of temperature on the dynamical process is also investigated.

gr-qc↗

arXiv2020

Critical Behaviour and Microscopic Structure of Charged AdS Black Hole with a Global Monopole in Extended and Alternate Phase Spaces

A detailed discussion on phase transition and microscopic structure of charged AdS black hole with a global monopole is presented in both extended and alternate phase spaces. In the analysis of critical behaviour, the classical van der Waals analogy is drawn from isotherms which is followed by Gibbs free energy study and coexistence curves. In both spaces, the symmetry breaking parameter $η$ acts as a hindrance for critical behaviour. The crux of van der Waals like behaviour is investigated by looking at the microscopic structure of the black hole via thermodynamic Ruppeiner geometry. The Ruppeiner invariant scalar behaves differently in extended and alternate spaces. The monopole parameter influences the microscopic structure of the black hole, which in turn, affects the critical behaviour. The effect is significant at the maximal strength of the monopole parameter.

gr-qc↗

arXiv2019

Joule-Thomson expansion in AdS black hole with a global monopole

In this paper, we investigate the Joule Thomson effects for AdS black holes with a global monopole. We study the effect of the global monopole parameter η on the inversion temperature and isenthalpic curves. The obtained result is compared with Joule Thomson expansion of van der Waals fluid and the equivalence were noted. Phase transition occuring in the extended phase space of this black hole is analogous to van der Waals gas. Our study shows that global monopole parameter η plays a very important role in Joule Thomson expansion.

gr-qc↗

arXiv2008

Aspects of Noncommutative Scalar/Tensor Duality

We study the noncommutative massless Kalb-Ramond gauge field coupled to a dynamical U(1) gauge field in the adjoint representation together with a compensating vector field. We derive the Seiberg-Witten map and obtain the corresponding mapped action to first order in $θ$. The (emergent) gravity structure found in other situations is not present here. The off-shell dual scalar theory is derived and it does not coincide with the Seiberg-Witten mapped scalar theory. Dispersion relations are also discussed. The p-form generalization of the Seiberg-Witten map to order $θ$ is also derived.

hep-th↗