arXiv subjects

Behzad Eslam Panah

Publications and source records attributed to Behzad Eslam Panah.

At least 19 recordsLinked to original sources

arXiv2026

Optical and Thermodynamic Signatures of Lorentz Symmetry Breaking in Bumblebee AdS Black Holes

We investigate the impact of spontaneous Lorentz symmetry breaking on scalar wave propagation, null geodesics, and thermodynamic behavior of four-dimensional asymptotically AdS black holes in bumblebee gravity. The static, spherically symmetric solutions are characterized by a dimensionless parameter $\ell > -1$ arising from the vacuum expectation value of the bumblebee vector field, which globally rescales the radial geometry. Massless scalar fields are analyzed via the radial Klein--Gordon equation cast into a generalized Helmholtz form, yielding an effective frequency-dependent refractive index that identifies oscillatory and evanescent regions, classical turning points, and confinement induced by curvature and Lorentz violation. In the high-frequency limit, wave propagation coincides with null geodesics, with $\ell$ controlling radial scaling and governing the geometric-optics limit. The AdS boundary reflects waves, while the horizon acts as a one-way absorber. Thermodynamic analysis in non-extended and extended phase spaces confirms the first law and Smarr relation, with $\ell$ influencing heat capacity, free energy, and stability. \textcolor{black}{Modeling these black holes as heat engines, we construct explicit cycles and show that efficiency increases with $\ell$, leading to an upper bound imposed by $η\leq 1$. Our results provide a framework connecting Lorentz violation, wave propagation, geometric optics, and AdS black hole thermodynamics in bumblebee gravity.

gr-qc↗

arXiv2026

Thermodynamics, Phase Transitions, and Geodesic Structure of F(R)-Phantom Banados-Teitelboim-Zanelli (BTZ) Black Holes

This paper investigates phantom BTZ black holes within the high-curvature gravity theory framework, specifically using a special case of power-Maxwell theory, which functions as a nonlinear electrodynamics source called F(R)-conformally invariant Maxwell gravity. We examine how the phantom or anti-Maxwell field affects the structure of these black holes and how the theory's parameters influence their horizon structure. Additionally, we derive the conserved and thermodynamic potentials associated with these black holes, thereby establishing their conformance to the foundational first law of thermodynamics. Next, the stability characteristics of BTZ black holes endowed with phantom and Maxwell fields are explored under canonical and grand canonical ensemble conditions by inspecting their heat capacity and Gibbs free energy profiles. This assessment reveals how the phantom field and scalar curvature affect these stability regions. We then perform a rigorous analytical verification of the Ehrenfest equations to determine whether the critical behavior of the phantom BTZ black hole corresponds to a second-order phase transition. Our results demonstrate adherence to both Ehrenfest relations, thereby confirming the occurrence of a second-order phase transition within the black hole system concurrent with the critical point. Furthermore, we explore the geodesic structure of the obtained solutions to analyze the motion of massive and massless test particles in the $F(R)$-phantom BTZ spacetime. The analysis demonstrates that stable timelike circular orbits exist only in the phantom regime for negative curvature backgrounds, while the phantom configuration also allows for stable circular photon orbits. These results underscore the significant influence of the phantom field and the F(R) correction on the spacetime geometry and orbital dynamics.

gr-qc↗

arXiv2026

Born-Infeld AdS Black Holes Surrounded by Perfect Fluid Dark Matter

We obtain exact charged AdS black hole solutions in Einstein Lambda gravity including the effects of Born Infeld nonlinear electrodynamics and Perfect Fluid Dark Matter. The influence of the PFDM and BI parameters on the event horizon is analyzed. We compute the conserved and thermodynamic quantities and verify that they satisfy the first law of thermodynamics. Thermal stability is studied in the canonical ensemble using the heat capacity and Helmholtz free energy showing how PFDM and BI parameters affect local and global stability regions. We further investigate the thermodynamics in the extended phase space by treating the cosmological constant as thermodynamic pressure obtaining consistent conserved quantities and confirming the first law. The Ehrenfest equations are analytically verified demonstrating that the critical behavior corresponds to a second order phase transition. Heat engines associated with these black holes are also constructed to examine how PFDM and BI parameters influence their efficiency. Finally we analyze the geodesic structure through timelike and null trajectories using the effective potential determining conditions for stable and unstable circular orbits the innermost stable circular orbit and the photon sphere. PFDM significantly modifies the orbital structure while BI corrections are weaker.

gr-qc↗

arXiv2025

Super-entropic black holes in gravity's rainbow and determining constraints on rainbow functions

This paper is motivated by the application of the inverse isoperimetric inequality to establish constraints on the parameters of gravity's rainbow. We investigate the thermodynamic (in)stability conditions for $d-$dimensional energy-dependent black holes, which are recognized as $d-$ dimensional black holes within the framework of gravity's rainbow. To achieve this, we calculate thermodynamic quantities such as Hawking temperature, entropy, total mass, and heat capacity in both extended and non-extended phase spaces for these black holes. We assess the physical and stable regions by utilizing these thermodynamic quantities alongside the inverse isoperimetric inequality, aiming to determine constraints on the rainbow functions. Finally, we show that by considering a constraint on the rainbow function, these black holes satisfy the super-entropic condition.

gr-qc↗

arXiv2024

Quasinormal modes and emission rate of ModMax (A)dS black holes

By considering a new model of nonlinear electrodynamics, known as the modified Maxwell (ModMax), and taking into account the topological and the cosmological constants in Einstein's gravity, we extract black hole solutions called Topological ModMax (A)dS black holes. The next step is to study the thermodynamic properties, quasinormal modes, and emission rates of these black holes in order to examine the impact of ModMax's parameter and the cosmological constant on these systems. To achieve this, we obtain the quasinormal spectra for massless scalar, electromagnetic, and Dirac perturbations. Additionally, we calculate null geodesics and determine the radius of the critical orbit. We then apply this information to derive the angular velocity and the Lyapunov exponent, which represent the real and imaginary terms of the quasinormal modes in the eikonal limit, respectively. Furthermore, we investigate the energy emission rate based on the discussion of null geodesics and the shadow radius.

gr-qc↗

arXiv2024

Thermodynamics and thermal stability of BTZ-ModMax black holes

Motivated by a new interesting nonlinear electrodynamics (NLED) model which is known as Modification Maxwell (ModMax) theory, we obtain an exact analytic BTZ black hole solution in the presence of a new NLED model and the cosmological constant. Then, by considering the obtained solution, we obtain Hawking temperature, entropy, electric charge, mass, and electric potential. We extract the first law of thermodynamics for the BTZ-ModMax black hole. We study thermal stability by evaluating the heat capacity (local stability) and Helmholtz free energy (global stability). By comparing the local and global stabilities, we find the common areas that satisfy the local and global stabilities, simultaneously.

gr-qc↗

arXiv2024

Analytic Electrically Charged Black Holes in $F(R)$-ModMax Theory

Motivated by a new model of nonlinear electrodynamics known as Modified Maxwell (ModMax) theory, an exact analytical solution for black holes is obtained by coupling ModMax nonlinear electrodynamics and $F(R)$ gravity. Then, the effects of the system's parameters ($F(R)$-ModMax gravity parameters) on the event horizons are analyzed. The obtained black holes thermodynamic properties in the $F(R)$-ModMax theory are investigated by extracting their thermodynamic quantities such as Hawking temperature, electric charge, electric potential, entropy, and also total mass. The first law of thermodynamics for the system under study is evaluated. Next, by considering these black holes, the impact of various parameters on both the local stability and global stability are investigated by examining the heat capacity and the Helmholtz free energy, respectively. Finally, the thermodynamic geometry of the black hole in $F(R)$-ModMax gravity is investigated by applying the thermodynamic metric (the HPEM metric).

gr-qc↗

arXiv2022

Neutron Stars in Mimetic Gravity

In this paper, a modified version of the hydrostatic equilibrium equation based on the mimetic gravity in the presence of perfect fluid is revisited. By using the different known equation of states, the structural properties of neutron stars are investigated in general relativity and mimetic gravity. Comparing the obtained results, we show that, unlike general relativity, we can find the appropriate equation of states that support observational data in the context of mimetic gravity. We also find that the results of relativistic mean-field-based models of the equation of states are in better agreement with observational data than non-relativistic models.

gr-qc↗

arXiv2021

Can the power Maxwell nonlinear electrodynamics theory remove the singularity of electric field of point-like charges at their locations?

YES! We introduce a variable power Maxwell nonlinear electrodynamics theory which can remove the singularity of electric field of point-like charges at their locations. One of the main problems of Maxwell's electromagnetic field theory is related to the existence of singularity for electric field of point-like charges at their locations. In other words, the electric field of a point-like charge diverges at the charge location which leads to an infinite self-energy. In order to remove this singularity a few nonlinear electrodynamics (NED) theories have been introduced. Born-Infeld (BI) NED theory is one of the most famous of them. However the power Maxwell (PM) NED cannot remove this singularity. In this paper, we show that the PM NED theory can remove this singularity, when the power of PM NED is less than $s<\frac{1}{2}$.

physics.class-ph↗

arXiv2019

Alternative approach to thermodynamic phase transitions

One of the major open problems in theoretical physics is a consistent quantum gravity theory.Recent developments in thermodynamic phase transitions ofblack holes and their van der Waals-like behavior may provide an interesting quantum interpretation of classical gravity. Studyingdifferent methods of investigating phase transitions can extend our insight into the nature of quantumgravity. In this paper, we present an alternative theoretical approach for finding thermodynamicphase transitions in the extended phase space. Unlike the standard methods based on the usualequation of state involving temperature, our approach usesa new quasi-equation constructed fromthe slope of temperature versus entropy. This approach addresses some of the shortcomings ofthe other methods, and provides a simple and powerful way of studying the critical behavior of athermodynamical system. Among the applications of this approach, we emphasize the analyticaldemonstration of possible phase transition points, and theidentification of the non-physical rangeof horizon radii for black holes.

gr-qc↗

arXiv2018

Thermal fluctuations of charged black holes in gravity's rainbow

Quantum fluctuation effects have an irrefutable role in high energy physics. Such fluctuation can be often regarded as a correction of infrared (IR) limit. In this paper, the effects of the first-order correction of entropy, caused by thermal fluctuation, on the thermodynamics of charged black holes in gravity's rainbow will be discussed. It will be shown that such correction has profound contributions to high energy limit of thermodynamical quantities, stability conditions of the black holes and interestingly has no effect on thermodynamical phase transitions. The coupling between gravity's rainbow and the first-order correction will be addressed. In addition, the measurement of entropy as a function of fluctuation of temperature will be done and it will be shown that de Sitter (dS) case enforces an upper limit on the values of temperature and produces cyclic like diagrams. While for the anti-de Sitter (AdS) case, a lower limit on the entropy is provided and although for special cases a cyclic like behavior could be observed, no upper or lower limit exists for the temperature. In addition, a comparison between non-correction and correction included cases on the thermodynamical properties of solutions will also be discussed and the effects of the first-order correction will be highlighted. It will be shown that the first-order correction provides the solutions with larger classes of thermal stability conditions which may result into existence of a larger number of thermodynamical structures for the black holes.

gr-qc↗

arXiv2018

Magnetic solutions in Einstein-massive gravity with linear and nonlinear fields

The solutions of $U(1)$ gauge-gravity coupling is one of the interesting models for analyzing the semi-classical nature of spacetime. In this regard, different well-known singular and nonsingular solutions have been taken into account. The paper at hand investigates the geometrical properties of the magnetic solutions by considering Maxwell and power Maxwell invariant (PMI) nonlinear electromagnetic fields in the context of massive gravity. These solutions are free of curvature singularity, but have a conic one which leads to presence of deficit/surplus angle. The emphasize is on modifications that these generalizations impose on deficit angle which determines the total geometrical structure of the solutions, hence, physical/gravitational properties. It will be shown that depending on the background spacetime (being anti de Sitter (AdS) or de Sitter (dS)), these generalizations present different effects and modify the total structure of the solutions differently.

gr-qc↗

arXiv2018

BTZ dilatonic black holes coupled to Maxwell and Born-Infeld electrodynamics

Motivated by string theory corrections of dilatonic gravity and Born-Infeld nonlinear electromagnetic field, we consider the BTZ black holes with these two generalizations. It will be shown that the generalization to dilatonic gravity introduces novel properties into thermodynamics of the black holes which were absent in the purely gravity case. Furthermore, the possibility of tuning out part of the dilatonic effects is explored in the Born-Infeld generalization.

physics.gen-ph↗

arXiv2017

Nonsingular universe in massive gravity's rainbow

One of the fundamental open questions in cosmology is whether we can regard the universe evolution without singularity like a Big Bang or a Big Rip. This challenging subject stimulates one to regard a nonsingular universe in the far past with an arbitrarily large vacuum energy. Considering the high energy regime in the cosmic history, it is believed that Einstein gravity should be corrected to an effective energy dependent theory which could be acquired by gravity's rainbow. On the other hand, employing massive gravity provided us with solutions to some of the long standing fundamental problems of cosmology such as cosmological constant problem and self acceleration of the universe. Considering these aspects of gravity's rainbow and massive gravity, in this paper, we initiate studying FRW cosmology in the massive gravity's rainbow formalism. At first, we show that although massive gravity modifies the FRW cosmology, but it does not itself remove the big bang singularity. Then, we generalize the massive gravity to the case of energy dependent spacetime and find that massive gravity's rainbow can remove the early universe singularity. We bring together all the essential conditions for having a nonsingular universe and the effects of both gravity's rainbow and massive gravity generalizations on such criteria are determined.

gr-qc↗

arXiv2017

Three dimensional dilatonic gravity's rainbow: exact solutions

Deep relations of dark energy scenario and string theory results into dilaton gravity, on one hand, and the connection between quantum gravity with gravity's rainbow, on the other hand, motivate us to consider three dimensional dilatonic black hole solutions in gravity's rainbow. We obtain two classes of the solutions which are polynomial and logarithmic forms. We also calculate conserved and thermodynamic quantities, and examine the first law of thermodynamics for both classes. In addition, we study thermal stability and show that one of the classes is thermally stable while the other one is unstable.

hep-th↗

arXiv2017

Nonsingular Universes in Gauss-Bonnet Gravity's Rainbow

In this paper, we will study the rainbow deformation of the FRW cosmology in both Einstein gravity and Gauss-Bonnet gravity. We will demonstrate that the singularity in the FRW cosmology can be removed because of the rainbow deformation of the FRW metric. We will obtain the general constraints required for the FRW cosmology to be free from singularities. It will be observed that the inclusion of Gauss-Bonnet gravity can significantly change the constraints required to obtain a nonsingular universes. We will use a rainbow functions motivated from the hard spectra of gamma-ray bursts to deform the FRW cosmology, and it will be explicitly demonstrated that such a deformation removes the singularity in the FRW cosmology.

gr-qc↗

arXiv2017

New perspective for black hole thermodynamics in Gauss-Bonnet-Born-Infeld massive gravity

Following earlier study regarding Einstein-Gauss-Bonnet-massive black holes in the presence of Born-Infeld nonlinear electromagnetic field [S. H. Hendi, B. Eslam Panah and S. Panahiyan, arXiv:1510.00108], we study thermodynamical structure and critical behavior of these black holes through various methods in this paper. Geometrical thermodynamics is employed to give a picture regarding phase transition of these black holes. Next, a new method is used to derive critical pressure and horizon radius of these black holes. In addition, Maxwell equal area law is employed to study the Van der Waals like behavior of these black holes. Moreover, the critical exponents are calculated and by using Ehrenfest equations, the type of the phase transitions are determined.

gr-qc↗

arXiv2016

Critical behavior of charged black holes in Gauss-Bonnet gravity`s rainbow

Following an earlier study regarding Gauss-Bonnet-Maxwell black holes in the presence of gravity's rainbow [S. H. Hendi and M. Faizal, Phys. Rev. D 92, 044027 (2015)], in this paper, we will consider all constants as energy dependent ones. The geometrical and thermodynamical properties of this generalization are studied and the validation of the first law of thermodynamics is examined. Next, through the use of proportionality between cosmological constant and thermodynamical pressure, van der Waals-like behavior of these black holes in extended phase space is investigated. An interesting critical behavior for sets of rainbow functions in this case is reported. Also, the critical behavior of uncharged and charged solutions is analyzed and it is shown that the generalization to a charged case puts an energy dependent restriction on values of different parameters.

gr-qc↗