arXiv subjects

B. Eslam Panah

Publications and source records attributed to B. Eslam Panah.

At least 19 recordsLinked to original sources

arXiv2026

Quasinormal modes of a quantum inspired black hole in four dimensions with cosmological constant

We study the scalar and Dirac perturbations of quantum-corrected black holes with cosmological constant. Using two different methods (WKB and double-null characteristic integration) we compute the quasinormal modes (QNMs) of de Sitter and Anti-de Sitter solutions considering linear field perturbations in the background geometry. In the limit of general relativity black holes our methods demonstrate good convergence with the available results in literature. In the presence of an extra quantum parameter we verify that all perturbations are stable evolving in towers of quasinormal oscillations. We scrutinize the spectra of both dS and AdS solutions studying the influence of that extra parameter in the frequencies.

gr-qc↗

arXiv2026

Charged Black Holes in Einstein--$U(1)$ Gravity with Letelier--Alencar Cloud of Strings: Thermodynamics and QPO-Based Observational Constraints

In this study, black hole solutions are derived within the framework of Einstein gravity, coupled to a $U(1)$ gauge field in the presence of both the Letelier--Alencar \textit{cloud of strings} and the cosmological constant. Subsequently, the influence of the \textit{cloud of strings} parameters and the electric charge on the structure of the event horizon is investigated. Conserved and thermodynamic quantities associated with these solutions are computed, and their consistency with the first law of black hole thermodynamics is verified. To assess the thermodynamic behavior of the system, the heat capacity and Gibbs potential are derived, thereby enabling an analysis of local and global stability under variations of the relevant parameters. Finally, the parameters of the proposed black hole solution are constrained via a Bayesian Markov Chain Monte Carlo (MCMC) analysis, utilizing observational quasi-periodic oscillation (QPO) data derived from stellar-mass, intermediate-mass, and supermassive black holes.

gr-qc↗

arXiv2026

Accelerating electrically charged ModMax black hole solutions in $F(R)$ gravity

Using the $C-$metric in the context of $F(R)$ gravity coupled with the ModMax nonlinear electromagnetic field (the $F(R)-$ModMax theory), we derive an exact black hole solution in a four-dimensional spacetime. We then examine how various parameters influence the behavior of accelerating ModMax black holes. Treating this black hole as a thermodynamic system, we calculate the Hawking temperature and entropy for the accelerating ModMax black holes within the framework of $F(R)$ gravity. Subsequently, we explore the impact of the parameters in $F(R)-$ModMax theory on the Hawking temperature and entropy. We also assess local stability by analyzing the heat capacity. Additionally, we investigate both the angular shadow and the shadow radius of an accelerating black hole in the context of $F(R)-$ModMax gravity.

gr-qc↗

arXiv2025

Topological Mod(A)Max AdS black holes

In this work, we construct new classes of topological black hole solutions in anti-de Sitter (AdS) spacetime using a novel model of nonlinear electrodynamics called Modification Maxwell (ModMax) and Modification phantom or Modification anti-Maxwell (ModAMax). We then evaluate the thermodynamic quantities and verify the first law of thermodynamics. Our study examines how the parameters of the ModMax and ModAMax fields, as well as the topological constant, affect the black hole solutions, thermodynamic quantities, and local and global thermal stabilities. Furthermore, within the framework of extended phase space thermodynamics, we analyze the Joule-Thomson expansion process and determine the inversion curves. This analysis reveals that the ModMax and ModAMax parameters significantly alter the cooling and heating behavior of these AdS black holes, depending on their topology. Finally, by treating these topological Mod(A)Max AdS black holes as heat engines, we assess their efficiencies, demonstrating that the parameters of nonlinear electrodynamics and horizon topology play crucial roles in enhancing or suppressing the system's thermodynamic performance.

gr-qc↗

arXiv2025

Some perspective of thermodynamical and optical properties of black holes in Maxwell-dilaton-dRGT-like massive gravity

Motivated by integrating the dilaton field (as a UV correction) with dRGT-like massive gravity (as an IR correction) into Einstein gravity, we investigate the thermodynamic and optical properties of black holes within this gravitational framework. We begin by reviewing the black hole solutions in Maxwell-dilaton-dRGT-like massive gravity, followed by an analysis of how various parameters influence on the asymptotical behavior of the spacetime and the event horizon of these black holes. In the subsequent section, we examine the conserved and thermodynamic quantities associated with these black holes, paying particular attention to the effects of parameters like $β$, $α$, and the massive parameters ($η_{1}$ and $η_{2}$) on their local stability by simultaneously evaluating the heat capacity and temperature. We also adopt an alternative method to study phase transitions using geometrothermodynamics. Furthermore, we explore how the parameters of Maxwell-dilaton-dRGT-like massive gravity impacts the optical characteristics and radiative behavior of black holes. In particular, we analyze the effects of the dilaton coupling constant ($α$), charge ($q$), the massive gravity parameter ($η_1$), and the graviton mass ($m_g$) on the radius of the photon sphere and the resulting black hole shadow. Moreover, the theoretical shadow radius is compared to the observational data from $Sgr A^*$. Additionally, we investigate the energy emission rate of these black holes, revealing that these parameters substantially influence the emission peak.

gr-qc↗

arXiv2025

Constraining the Neutron-Star Equation of State via Short Gamma-Ray Burst X-ray Afterglows

Recent observations from NICER in X-rays and LIGO/Virgo in gravitational waves have provided critical constraints on the mass, radius, and tidal deformability of neutron stars, imposing stringent limits on the equation of state (EOS) and the behavior of ultra-dense matter. However, several key parameters influencing the EOS, such as the maximum mass of neutron stars, spin-down rates, and the potential role of exotic matter in their cores, remain subject of ongoing debate. Here we present a new approach to constraining the EOS by analyzing the X-ray afterglows of some short gamma-ray bursts, focusing on "the internal plateau" phase and its abrupt decay, which reflect the spin-down and possible collapse of a supra-massive neutron star into a black hole. By linking critical neutron star masses with black hole formation criteria and the observational data from Swift's BAT and XRT instruments with compact object models, we explore three representative EOSs that range from "soft" to "stiff". Our result supports a maximum mass for neutron stars of approximately 2.39 solar masses at the threshold of black hole formation. This conclusion holds under assumptions of magnetar-powered X-ray plateaus, constant radiative efficiency, isotropic emission, and full Kerr black hole energy extraction; deviations could influence the inferred results. Our results demonstrate the critical role of neutron star/black hole physics in probing dense nuclear matter and provide a novel framework for exploring extreme astrophysical environments.

astro-ph.HE↗

arXiv2025

Black hole solutions in theory of ModMax-dRGT-like massive gravity

This paper explores the properties of black holes using a new model of nonlinear electrodynamics called modified Maxwell (ModMax), in conjunction with nonlinear massive gravity known as dRGT-like massive gravity. We start by deriving the exact black hole solutions within the framework of ModMax-dRGT-like massive gravity and analyze how the parameters of both ModMax and dRGT-like massive gravity influence the characteristics of these black holes. Additionally, we calculate the thermodynamic quantities for these black holes in the non-extended phase space and investigate how the parameters of ModMax and dRGT-like massive gravity affect these quantities. We confirm that these quantities satisfy the first law of thermodynamics. We also examine local stability by analyzing heat capacity and assess how ModMax and the massive parameters influence phase transitions and physical limitation points. Next, we expand our analysis to the extended phase space, demonstrating that these thermodynamic quantities satisfy both the first law of thermodynamics and the Smarr relation in this context. Finally, we examine the isoperimetric ratio of black holes in ModMax-dRGT-like massive gravity.

gr-qc↗

arXiv2025

Super-entropy bumblebee AdS black holes

Motivated by the effect of the bumblebee field on thermodynamic instability in (non)extended phase space, we study the thermodynamic instability for the bumblebee AdS black holes. For this purpose, first, we evaluate the effect of the bumblebee field (or Lorentz-violating parameter) on the event horizon for AdS black holes. Then, in non-extended phase space, we study the effect of the bumblebee field on the heat capacity and the Helmholtz free energy to investigate the local and global thermal stability areas, respectively. Next, we extend our study on the extended phase space by seeking on stable area by using the heat capacity at constant pressure ($C_{P}$). Finally, we evaluate the super-entropy black hole condition and indicate that the bumblebee AdS black holes are super-entropy black holes when $l>0$, which is consistent with the condition $C_{P}<0$.

gr-qc↗

arXiv2024

Thermodynamic topology of topological black hole in $F(R)$-ModMax gravity's rainbow

In order to include the effect of high energy and topological parameters on black holes in $F(R)$ gravity, we consider two corrections to this gravity: energy-dependent spacetime with different topological constants, and a nonlinear electrodynamics field. In other words, we combine $F(R)$ gravity's rainbow with ModMax nonlinear electrodynamics theory to see the effects of high energy and topological parameters on the physics of black holes. For this purpose, we first extract topological black hole solutions in $F(R)$% -ModMax gravity's rainbow. Then, by considering black holes as thermodynamic systems, we obtain thermodynamic quantities and check the first law of thermodynamics. The effect of the topological parameter on the Hawking temperature and the total mass of black holes is obvious. We also discuss the thermodynamic topology of topological black holes in $F(R)$-ModMax gravity's rainbow using the off-shell free energy method. In this formalism, black holes are assumed to be equivalent to defects in their thermodynamic spaces. For our analysis, we consider two different types of thermodynamic ensembles. These are: fixed $q$ ensemble and fixed $ϕ$ ensemble. We take into account all the different types of curvature hypersurfaces that can be constructed in these black holes. The local and global topology of these black holes are studied by computing the topological charges at the defects in their thermodynamic spaces. Finally, in accordance with their topological charges, we classify the black holes into three topological classes with total winding numbers corresponding to $-1, 0$, and $1$. We observe that the topological classes of these black holes are dependent on the value of the rainbow function, the sign of the scalar curvature, and the choice of ensembles.

hep-th↗

arXiv2024

Thermodynamic topology of topological charged dilatonic black holes

The aim of this paper is to explore the thermodynamic topology of topological charged dilatonic black holes. To achieve this, our study will begin by examining the characteristics of topological charged black holes in dilaton gravity. Specifically, we will concentrate on the impact of the topological constant on the event horizon of these black holes. Subsequently, we will analyze these black holes, considering their thermodynamic and conserved quantities, in order to assess the validity of the first law of thermodynamics. We explore the thermodynamic topology of these black holes by treating them as thermodynamic defects. For our study, we examine two types of thermodynamic ensembles: the fixed $q$ ensemble and the fixed $ϕ$ ensemble. To study the impact of the topological constant ($% k$) on thermodynamic topology, we consider all possible types of curvature hypersurfaces that can form in these black holes. By calculating the topological charges at the defects within their thermodynamic spaces, we analyze both the local and global topology of these black holes. We also investigate how the parameters of dilaton gravity affect the thermodynamic topology of black holes and highlight the differences compared to charged black holes in the General Relativity.

hep-th↗

arXiv2024

Phantom BTZ black holes

Motivated by the impact of the phantom field (or anti-Maxwell field) on the structure of three-dimensional black holes in the presence of the cosmological constant, we present the first extraction of solutions for the phantom BTZ (A)dS black hole. In this study, we analyze the effect of the phantom field on the horizon structure. Furthermore, we compare the BTZ black holes in the presence of both the phantom and Maxwell fields. Additionally, we calculate the conserved and thermodynamic quantities of the phantom BTZ black holes, demonstrating their compliance with the first law of thermodynamics. Subsequently, we assess the effects of the electrical charge and the cosmological constant on the local stability in the canonical ensemble by considering these fields with respect to the heat capacity. We then investigate the global stability area of the BTZ black holes with phantom and Maxwell fields within the grand canonical ensemble using Gibbs free energy. In this analysis, we evaluate the influence of the electrical charge and the cosmological constant on this area.

gr-qc↗

arXiv2024

Three-dimensional AdS black holes in massive-power-Maxwell theor

Recently, it was shown that the power-Maxwell (PM) theory could remove the singularity of the electric field \cite{PM2}. Motivated by a great interest in three-dimensional black holes and a surge of success in studying massive gravity from both the cosmological and astrophysical points of view, we investigate three-dimensional black hole solutions in de Rham, Gabadadze, and Tolley (dRGT) massive theory of gravity in the presence of PM electrodynamics. First, we extract exact three-dimensional solutions in this theory of gravity. Then we study the geometrical properties of these solutions. Calculating conserved and thermodynamic quantities, we check the validity of the first law of thermodynamics for these black holes. We also examine the stability of these black holes in the context of the canonical ensemble. We continue calculating this kind of black hole's optical features, such as the photon orbit radius, the energy emission rate, and the deflection angle. Considering these optical quantities, finally, we analyze the effective role of the parameters of models on them.

physics.gen-ph↗

arXiv2024

Accelerating AdS black holes in gravity's rainbow

Motivated by the effect of the energy of moving particles in $C-$metric, we first obtain exact accelerating black hole solutions in gravity's rainbow. Then, we study the effects of gravity's rainbow and $C-$metric parameters on the Ricci and Kretschmann scalars, and also the asymptotical behavior of this solution. Next, we indicate how different parameters of the obtained accelerating black holes in gravity's rainbow affect thermodynamics quantities (such as the Hawking temperature, and entropy) and the local stability (by evaluating the heat capacity). In the following, we extract the geodesic equations to determine the effects of various parameters on photon trajectory in the vicinity of this black hole, as well as obtain the radius of the photon sphere and the corresponding critical impact parameter to gain insight into AdS black hole physics by adding the gravity's rainbow to $C-$metric.

gr-qc↗

arXiv2024

Quark stars in massive gravity might be candidates for the mass gap objects

We have investigated the structural properties of strange quark stars (SQSs) in a modified theory of gravity known as massive gravity. In order to obtain the equation of state (EOS) of strange quark matter, we have employed a modified version of the Nambu-Jona-Lasinio model (MNJL) which includes a combination of NJL Lagrangian and its Fierz transformation by using weighting factors ($1-α$) and $α$. Additionally, we have also calculated dimensionless tidal deformability ($Λ$) in massive gravity. To constrain the allowed values of the parameters appearing in massive gravity, we have imposed the condition $Λ_{1.4 {M}_{\odot }}\lesssim580 $. Notably, in the MNJL model, the value of $α$ varies between zero and one. As $α$ increases, the EOS becomes stiffer, and the value of $Λ$ increases accordingy. We have demonstrated that by softening the EOS with increasing the bag constant, one can obtain objects in massive gravity that not only satisfy the constraint $Λ_{1.4 {M}% _{\odot }}\lesssim580$, but they also fall within the unknown mass gap region ($2.5{M}_{\odot}-5{M}_{\odot }$). To establish that the obtained objects in this region are not black holes, we have calculated Schwarzschild radius, compactness, and $Λ_{M_{TOV}}$ in massive gravity.

gr-qc↗

arXiv2024

Thermodynamics and Optical Properties of Phantom AdS Black Holes in Massive Gravity

Motivated by high interest in Lorentz invariant massive gravity models known as dRGT massive gravity, we present an exact phantom black hole solution in this theory of gravity and discuss the thermodynamic structure of the black hole in the canonical ensemble. Calculating the conserved and thermodynamic quantities, we check the validity of the first law of thermodynamics and the Smarr relation in the extended phase space. In addition, we investigate both the local and global stability of these black holes and show how massive parameters affect the regions of stability. We extend our study to investigate the optical features of the black holes such as the shadow geometrical shape, energy emission rate, and deflection angle. Also, we discuss how these optical quantities are affected by massive coefficients. Finally, we consider a massive scalar perturbation minimally coupled to the background geometry of the black hole and examine the quasinormal modes (QNMs) by employing the WKB approximation.

gr-qc↗

arXiv2023

Effect of rainbow function on the structural properties of dark energy star

Confirming the existence of compact objects with a mass greater than $2.5M_{\odot}$ by observational results such as GW190814 makes that is possible to provide theories to justify these observational results using modified gravity. This motivates us to use gravity's rainbow, which is the appropriate case for dense objects, to investigate the dark energy star structure as a suggested alternative case to the mass gap between neutron stars and black holes in the perspective of quantum gravity. Hence, in the present work, we derive the modified hydrostatic equilibrium equation for an anisotropic fluid, represented by the extended Chaplygin equation of state in gravity's rainbow. Then, for two isotropic and anisotropic cases, using the numerical solution, we obtain energy-dependent maximum mass and its corresponding radius, and the other properties of the dark energy star including the pressure, energy density, stability, etc. In the following, using the observational data, we compare the obtained results in two frameworks of general relativity and gravity's rainbow.

gr-qc↗

arXiv2023

Structure of $3D$ gravastars in the context of massive gravity

In this paper, we investigate a new model of $(2+1)-$dimensional ($3D$) gravitational vacuum stars (gravastars) with an isotropic matter distribution anti-de Sitter (AdS) spacetime in the context of massive gravity. For this purpose, we explore free singularity models with a specific equation of state. Using Mazur-Mottola's approach, we predict $3D$ gravastars as alternatives to BTZ black holes in massive gravity. We find analytical solutions to the interior of gravastars free of singularities and event horizons. For a thin shell containing an ultra-relativistic stiff fluid, we discuss length, energy, and entropy. In conclusion, the parameter of massive gravity plays a significant role in predicting the proper length, energy contents and entropyand parameters of gravastars.

gr-qc↗

arXiv2023

Effect of massive graviton on dark energy star structure

The presence of massive gravitons in the field of massive gravity is considered as an important factor in investigating the structure of compact objects. Hence, we are encouraged to study the dark energy star structure in the Vegh's massive gravity. We consider that the equation of state governing the inner spacetime of the star is the extended Chaplygin gas, and then using this equation of state, we numerically solve the Tolman-Oppenheimer-Volkoff (TOV) equation in massive gravity. In the following, assuming different values of free parameters defined in massive gravity, we calculate the properties of dark energy star such as radial pressure, transverse pressure, anisotropy parameter, and other characteristics. Then, after obtaining the maximum mass and its corresponding radius, we compute redshift and compactness. The obtained results show that for this model of dark energy star, the maximum mass and its corresponding radius depend on the massive gravity's free parameters and anisotropy parameter. These results are consistent with the observational data, and cover the lower mass gap. We also demonstrate that all energy conditions are satisfied for this model, and in the presence of anisotropy, the dark energy star is potentially unstable.

gr-qc↗