arXiv subjects

Dharm Veer Singh

Publications and source records attributed to Dharm Veer Singh.

At least 19 recordsLinked to original sources

arXiv2026

Thermodynamics, Shadow, and Quasinormal Modes of AdS Ayón--Beato--García Massive Black Hole

We investigate the thermodynamics, photon sphere, and dynamical stability of an AdS Ayón--Beato--García (ABG) massive black hole with graviton mass and magnetic charge. The Gibbs free energy exhibits distinct limiting behaviors: it reduces to that of an AdS massive black hole when magnetic charge vanishes, to that of an AdS ABG black hole when graviton mass is zero, and smoothly interpolates to the AdS massive Reissner-Nordström case in the asymptotic regime. Furthermore, the photon sphere and shadow analysis indicate that increasing the graviton mass expands their radii, while increasing the magnetic charge causes contraction, in agreement with earlier studies of black hole spacetimes. Quasinormal mode (QNM) calculations further confirm dynamical stability, as the imaginary part remains negative, ensuring decay of perturbations. Additionally, the real part of the frequency decreases with graviton mass, while the imaginary part initially grows before saturating at higher values. Together, these results provide meaningful insights into the interplay between graviton mass, magnetic charge, and stability, thereby enriching the understanding of black holes in modified gravity theories.

gr-qc↗

arXiv2026

More Exact Thermodynamic Analysis of Topological Black Holes in $R^2$ Gravity

This study investigates the thermodynamics of topological black hole solutions in $R^{2}$ gravity, incorporating the effects of small statistical fluctuations up to first-order corrections. We precisely calculate entropy, internal energy, Helmholtz free energy, specific heat, enthalpy, and Gibbs free energy, accounting for perturbative thermal corrections. Our results reveal that the internal energy of small black holes diverges asymptotically due to these fluctuations. The corrected Gibbs free energy attains asymptotically high values for small horizon radii. In contrast, the equilibrium Gibbs free energy approaches zero. Additionally, we assess the stability of the black hole in the presence of these thermal fluctuations. We find that, in contrast to the equilibrium state, the thermal fluctuation introduces a double phase transition to the stability of the black hole. Our analysis reveals that the influence of fluctuations is notably significant, primarily for small black holes. These findings offer new insights into the thermodynamic properties of topological black holes in the presence of thermal fluctuations.

gr-qc↗

arXiv2025

Exploring non-perturbative effects on quasi-topological black hole thermodynamics

We examine the impact of non-perturbative quantum corrections to the entropy of both charged and charged rotating quasi-topological black holes, with a focus on their thermodynamic properties. The negative-valued correction to the entropy for small black holes is found to be unphysical. Furthermore, we analyze the effect of these non-perturbative corrections on other thermodynamic quantities, including internal energy, Gibbs free energy, charge density, and mass density, for both types of black holes. Our findings indicate that the sign of the correction parameter plays a crucial role at small horizon radii. Additionally, we assess the stability and phase transitions of these black holes in the presence of non-perturbative corrections. Below the critical point, both the corrected and uncorrected specific heat per unit volume are in an unstable regime. This instability leads to a first-order phase transition, wherein the specific heat transitions from negative to positive values as the system reaches a stable state.

gr-qc↗

arXiv2025

Impact of Perfect Fluid Dark Matter on the Thermodynamics of $AdS$ Ayón--Beato--García Black Holes

In this paper, we derive the black hole solution in the context of nonlinear electrodynamics (NLED) coupled to a perfect fluid dark matter (PFDM) field. The resulting black hole solution interpolates between the $AdS$ Ayón--Beato--García (ABG) black hole in the absence of the PFDM field and the Schwarzschild black hole devoid of magnetic monopole charges and PFDM influence. A numerical investigation of the horizon structure and thermodynamic properties, including both local and global stability, is conducted for the obtained black hole solution. The thermodynamic quantities are shown to be modified by the presence of the NLED and PFDM fields. We observe that the behaviour of thermodynamical quantities of black holes depends on these parameters significantly. We also discuss the stability and phase transition dependency on these parameters.

gr-qc↗

arXiv2024

Ayón--Beato--García black hole coupled with a cloud of strings: thermodynamics, shadows and quasinormal modes

We find an exact black hole solution for the Einstein gravity in the presence of Ayón--Beato--García non-linear electrodynamics and a cloud of strings. The resulting black hole solution is singular, and the solution becomes non-singular when gravity is coupled with Ayón--Beato--García non-linear electrodynamics only. This solution interpolates between Ayón--Beato--García black hole, Letelier black hole and Schwarzschild black hole { in the absence of cloud of strings parameter, magnetic monopole charge and both of them, respectively}. We also discuss the thermal properties of this black hole and find that the solution follows the modified first law of black hole thermodynamics. Furthermore, we estimate the solution's black hole shadow and quasinormal modes.

gr-qc↗

arXiv2024

Thermodynamics of a newly constructed black hole coupled with nonlinear electrodynamics and cloud of strings

This paper finds an exact singular black hole solution in the presence of nonlinear electrodynamics as the source of matter field surrounded by a cloud of strings in $4D$ $AdS$ spacetime. Here, the presence of the cloud of string, the usual Bardeen solution, becomes singular. The obtained black hole solution interpolates with the $AdS$ Letelier black hole in the absence of both the deviation parameter and magnetic charge and interpolates with the $AdS$ Bardeen black hole in the absence of the deviation parameter and a cloud of strings parameter. We analyse the horizon structure and thermodynamics properties, including the stability of the resulting black hole, numerically and graphically. Thermodynamical quantities associated with the black hole get modified due to the nonlinear electrodynamics and cloud of strings. Moreover, we study the effect of a cloud of strings parameter, magnetic charge and deviation parameter on critical points and phase transition of the obtained black hole where the cosmological constant is treated as the thermodynamics pressure. The critical radius increases with increasing deviation parameter values and magnetic charge values. In contrast, the critical pressure and temperature decrease with increasing deviation parameters and magnetic charge values.

gr-qc↗

arXiv2024

Non-perturbative correction on the black hole geometry

In this paper, we use the holographic principle to obtain a modified metric of black holes that reproduces the exponentially corrected entropy. The exponential correction of the black hole entropy comes from non-perturbative corrections. It interprets as a quantum effect which affects black hole thermodynamics especially in the infinitesimal scales. Hence, it may affect black hole stability at the final stage. Then, we study modified thermodynamics due to the non-perturbative corrections and calculate thermodynamics quantities of several non-rotating black holes.

gr-qc↗

arXiv2024

(Anti-)BRST Symmetries in FLRW Model: Supervariable Approach

Friedmann-Lemaitre-Robertson-Walker (FLRW) model, representing the isotropic and homogeneous Universe, has an inherent diffeomorphism (or reparametrization) invariance. For a given local time-reparametrization symmetry transformation of (0+1)-dimensional (1D) diffeomorphism invariant FLRW model, we derive the off-shell nilpotent and absolutely anticommuting (anti-)BRST symmetry transformations in a consistent manner. The supervariable approach to BRST formalism is used as a guiding tool in finding the proper (anti-)BRST transformations. An application of (super-)diffeomorphism invariance, in the context of superspace formalism, yields horizontality conditions. Moreover, the celebrated CF-type condition which is universal for 1D diffeomorphism invariant theories, emerges as an off-shoot of the horizontality condition and provides the absolute anticommutativity of the (anti-)BRST transformations. In addition, this CF-type condition leads to the derivation of coupled (but equivalent) (anti-)BRST invariant quantum Lagrangians for FLRW model. We also capture the geometrical interpretation of the (anti-)BRST transformations and their properties in terms of the Grassmannian translational generators and supervariables.

hep-th↗

arXiv2023

Exact Solution of Bardeen Black Hole in Einstein-Gauss-Bonnet gravity

We have obtained a new exact regular black hole solution for the EGB gravity coupled with nonlinear electrodynamics in AdS space. The numerical analysis of horizon structure suggests two horizons exist: Cauchy and event. We also study the thermal properties of this black hole, which satisfy the modified first law of thermodynamics. Moreover, we analyse the local and global stability of the black hole. The $P-V$ criticality and phase transition are also discussed. The critical exponents for the present model exactly match the mean field theory.

gr-qc↗

arXiv2023

Parameter estimation of the Bardeen-Kerr black hole in cloud of strings using shadow analysis

We consider the rotating generalization of the Bardeen black hole solution in the presence of cloud of strings (CoS). The parameter space for which the black hole horizon exists is determined. We also study the static limit surface and the ergo-region in the presence of the CoS parameter. We consider photon orbits and obtain the deformation of black hole shadows due to rotation for various values of CoS parameter. The shadow deformation is used to determine the black hole spin for different values of the black hole parameters.

gr-qc↗

arXiv2023

Charged $AdS$ Black Holes in $4D$ Einstein--Gauss--Bonnet Massive Gravity

We investigate Einstein--Gauss--Bonnet--Maxwell massive gravity in $4D$ AdS background and find an exact black hole solution. The horizon structure of the black holes studied. Treating the cosmological constant as pressure and Gauss-Bonnet coupling parameters, and massive gravity parameters as variables, we drive the first law of black hole thermodynamics. To study the global stability of the black holes we compute the Gibbs free energy. The local stability of the black hole is also studied through specific heat. We analyze the effects of graviton mass and Gauss-Bonnet coupling parameters on the phase transition of the black holes. Finally, the effects of graviton mass and massive gravity parameters on the Joule-Thomson expansion of the black hole are studied.

gr-qc↗

arXiv2023

More Exact Thermodynamics of Nonlinear Charged AdS Black Holes in 4D Critical Gravity

In this paper, we investigate nonlinearly charged AdS black holes in four-dimensional critical gravity and study more exact black hole thermodynamics under the effect of small statistical fluctuations. We compute the correction to the thermodynamics of nonlinearly charged AdS black hole up to the leading order. We discuss the stability of black holes under the circumstances of fluctuation and find that fluctuation causes instability in the black holes. Moreover, both the isothermal and adiabatic compressibilities are also derived. Finally, we estimate the role of small fluctuations on the equation of states and study the $P-v$ diagram of nonlinearly charged AdS black hole.

gr-qc↗

arXiv2023

Quasinormal Modes and Phase Structure of Regular $AdS$ Einstein-Gauss-Bonnet Black Holes

In this paper, we present an exact regular black hole solution in Einstein-Gauss-Bonnet coupled with nonlinear matter fields. It is a generalization of a regular Einstein-Gauss-Bonnet black hole in $5D$ $AdS$ spacetime. The causal structure of the obtained solution identifies with Boulware-Deser black hole solution, except for the curvature singularity at the center. It incorporates the Boulware-Deser black holes in the absence of deviation parameters. We also study the thermodynamic properties of the solution that satisfies a modified first law of thermodynamics. Furthermore, we discuss the stability of the obtained black hole solution and, in this regard, a double phase transition occurs. Within context, we find that phase transition exists at the point where the heat capacity diverges and, incidentally, the temperature attains the maximum value. We discuss the fluid nature of the black hole also exhibiting critical points. The quasinormal modes of the black hole solution and their dependencies on Gauss-Bonnet coupling and deviation parameters are also analysed in terms of null geodesics.

gr-qc↗

arXiv2023

Shadows and quasinormal modes of the Bardeen black hole in cloud of strings

We investigate the black hole (BH) solution of the Einstein's gravity coupled with non-linear electrodynamics (NED) source in the background of a cloud of strings. We analyze the horizon structure of the obtained BH solution. The optical features of the BH are explored. The photon radius and shadows of the BH are obtained as a function of black hole parameters. We observe that the size of the shadow image is bigger than its horizon radius and photon sphere. We also study the Quasinormal modes (QNM) using WKB formula for this black hole. The dependence of shadow radius and QN modes on black hole parameters reflects that they are mimicker to each other.

gr-qc↗

arXiv2022

Quasinormal modes, shadow and thermodynamics of black holes coupled with nonlinear electrodynamics and cloud of strings

We construct an exact black hole solution for the Einstein gravity coupled with the nonlinear electrodynamics (which corresponds to the Maxwell electrodynamics in the weak field limit) in the presence of a cloud of strings as the source. We study the thermodynamical properties of the black hole solutions and derive the corrected first-law of thermodynamics. The presence of a cloud of strings does not affect the stability of the present black hole. However, a second-order phase transition exists for this system at a critical horizon radius. Furthermore, we study the quasinormal modes and their shadow radius. In addition, we find that, upon variation, the parameters of the theory show different aspects of the optical characteristics of the black hole solutions.

gr-qc↗

arXiv2022

Corrected thermodynamics of $(2+1)D$ black hole conformally coupled to a massless scalar

We study the corrected entropy due to thermal fluctuation and their effect on the thermodynamics of a conformally dressed black hole in three dimensions. We find that the thermal fluctuation affects the entropy significantly for small black holes. Various corrected thermodynamical variables are also calculated for this black hole. We observe that thermal fluctuation on the thermodynamics of a small conformal black hole has a significant effect. We also analyse the stability of black hole under the effect of thermal fluctuation. Due to thermal fluctuation, instability occurs in the system of small conformal black holes. Isothermal compressibility is also studied for this black hole which diverges for the equilibrium state of the system.

gr-qc↗

arXiv2022

Thermodynamic properties, thermal image and phase transition of Einstein-Gauss-Bonnet black hole coupled with nonlinear electrodynamics

We obtain an exact solution of $AdS$ black hole solution in Einstein-Gauss-Bonnet (EGB) gravity coupled with nonlinear electrodynamics. It interpolates with the $AdS$ regular black hole and $AdS$ EGB black hole in the absence of the Gauss-Bonnet coupling constant and both magnetic monopole charge and deviation parameter, respectively. Based on horizon thermodynamics, we study the thermodynamic properties of the obtained solution (e.g. mass, temperature, entropy, heat capacity and free energy). The Hawking temperature of the nonsingular black hole gets the maximum value at the point where specific heat diverges and the second-order phase transition occurs at the same point. We find that the smaller nonsingular black holes are stable due to positive heat capacity and negative free energy. We explicitly trace the relations between the black hole shadow and the critical behavior of charged EGB $AdS$ regular black hole in the extended phase space.

gr-qc↗

arXiv2022

How are the degrees of freedom responsible for entropy in BTZ spacetime?

The entanglement entropy approach to study the dependence of entropy upon the location of degrees of freedom (dof) (near/far) from the horizon is discussed in this article. We try to understand the physical deviation of the area law for the excited states by incorporating the logarithmic and power law corrections. We show that the dof near the horizon gives contribution to the total entropy of the system in the ground state and away from the event horizon gives contribution to the excited state.

hep-th↗