arXiv subjects

Behnam Pourhassan

Publications and source records attributed to Behnam Pourhassan.

At least 55 records · Page 3Linked to original sources

arXiv2025

Observational analysis of bulk viscous modified Chaplygin gas in (2+1)-dimensional universe using MCMC

This paper investigates regarding cosmological implications of a bulk viscous modified Chaplygin gas (MCG) in (2+1)-dimensional Friedmann-Robertson-Walker spacetime, incorporating both theoretical analysis and observational constraints. We derive analytical solutions for both viscous and non-viscous cases, revealing distinct behavior in energy density evolution, Hubble parameter dynamics, and deceleration parameter transitions. A comprehensive perturbation analysis illustrates how bulk viscosity dampens the structure growth oscillations, addressing a key challenge faced by Chaplygin gas models in higher dimensions. Using Markov chain Monte Carlo (MCMC) techniques with Hubble parameter and Pantheon supernova datasets, we impose constraints on our model parameters, obtaining $H_0 = 67.90$ km s$^{-1}$ Mpc$^{-1}$, showing remarkable consistency with Planck $Λ$CDM estimations despite the dimensional reduction. Our findings suggest that lower-dimensional viscous cosmology captures essential features of cosmic evolution while providing valuable theoretical insights into the interplay between dissipative effects and exotic equations of state.

gr-qc↗

arXiv2025

Assessing WGC Compatibility in ModMax Black Holes via Photon Spheres Analysis and WCCC Validation

It seems that the regime of Hawking radiation and evaporation ultimately drives charged black holes toward super-extremality of the charge parameter and the dominance of extremal conditions. This progression, in turn, lays the groundwork for satisfying the necessary conditions for the Weak Gravity Conjecture (WGC). Preliminary studies indicate that black holes such as the Reissner-Nordstr$ö$m (RN) model, in their initial form, lack the capacity to sustain super-extremality of the charge parameter. If such conditions arise, these black holes transition into naked singularities-a scenario that is highly undesirable due to the loss of causality and the breakdown of space-time geometry. This raises whether the inability to sustain super-extremality is an inherent property of the model or a consequence of the approximations and precision limitations employed in its construction. To address this, we turned to the ModMax model, which represents an extension of the RN model. Our analysis revealed that the ModMax model not only accommodates super-extremality of the charge parameter but also, under certain conditions, emerges as a promising candidate for investigating the WGC. Furthermore, we independently observed how the inclusion of the de Sitter radius ($\ell$) in the AdS model and $f(R)$ gravitational corrections-both of which enhance and complicate the model-can have a direct impact on the range of super-extremal charge tolerance which, in turn, provides the realization of the conditions necessary for the WGC.

hep-th↗

arXiv2025

On the microstructure of higher-dimensional Reissner-Nordström black holes in quantum regime

Thermodynamic Riemannian geometry provides great insights into the microscopic structure of black holes (BHs). One such example is the Ruppeiner geometry which is the metric space comprising the second derivatives of entropy with respect to other extensive variables of the system. Reissner-Nordström black holes (RNBHs) are known to be endowed with a flat Ruppeiner geometry for all higher spacetime dimensions. However this holds true if one invokes classical gravity where the semi-classical Bekenstein-Hawking entropy best describes the thermodynamics of the system. If the much deeper quantum gravity and string theories entail modifications to BH entropy, this prompts the question whether the Ruppeiner flatness associated with higher dimensional RNBHs still persists. We investigate this problem by considering non-perturbative (exponential) and perturbative (logarithmic) modifications to BH entropy of a 5D RNBH. We find that while the case is so for larger (classical) geometries, the situation is radically altered for smaller (quantum) geometries. Namely, we show surprising emergence of multiple phase transitions that depend on the choice of extent of corrections to BH entropy and charge. Our consideration involves differentiated extremal and non-extremal geometric scales corresponding to the validity regime of corrections to entropy. More emphasis is laid on the exponential case as the contributions become highly non-trivial on small scales. An essential critical mass scale arises in this case that marks the onset of these phase transitions while the BH diminishes in size via Hawking evaporation. We contend that this critical value of mass perhaps best translates as the epoch of a classical to quantum BH phase transition.

gr-qc↗

arXiv2025

Reconciling the Weak Gravity and Weak Cosmic Censorship Conjectures in Einstein-Euler-Heisenberg-AdS Black Holes

The potential conflict between the Weak Gravity Conjecture (WGC) and the Weak Cosmic Censorship Conjecture (WCCC) poses a significant challenge in general relativity. The WCCC serves as a fundamental assumption ensuring the coherence of gravitational theory. This study investigates the reconciliation of the WGC and the WCCC by examining Einstein-Euler-Heisenberg-AdS black holes in four-dimensional spacetime. By imposing specific constraints on the metric parameters, we demonstrate that the WGC and the WCCC can coexist harmoniously. Detailed analyses of Einstein-Euler-Heisenberg-AdS black holes for $ Q > M $ validate the simultaneous fulfillment of the two conjectures, particularly in scenarios where $ q^2/m^2 \geq \left(Q^2 / M^2\right)_{\text{e}} $. The electromagnetic self-interaction parameter $ μ$ plays a crucial role in achieving this compatibility. Our findings establish that Einstein-Euler-Heisenberg-AdS black holes provide a robust framework for harmonizing the WGC and the WCCC. In particular, for exceedingly small values of ($μ$)-or, equivalently, when the condition ($μ\ll \ell$) is satisfied-the structure of our black hole transitions in a way that distinctly reveals its compatibility with the WGC. This study also explores the compatibility of the WGC and the WCCC with photon spheres. It examines parameter spaces that satisfy both conjectures, ensuring event horizons and photon spheres while maintaining black hole properties. Key results demonstrate that small $ μ$ values preserve WCCC adherence and validate WGC through photon sphere characteristics.

gr-qc↗

arXiv2025

Thermodynamic topology of Black Holes in $F(R)$-Euler-Heisenberg gravity's Rainbow

The topology of black hole thermodynamics is a fascinating area of study that explores the connections between thermodynamic properties and topological features of black holes. We successfully derive the field equations for $F(R)$-Euler-Heisenberg theory, providing a framework for studying the interplay between modified gravity and non-linear electromagnetic effects. We obtain an analytical solution for a static, spherically symmetric, energy-dependent black hole with constant scalar curvature. Also, our analysis of black holes in F(R)-Euler-Heisenberg gravity's Rainbow reveals significant insights into their topological properties. We identified the total topological charges by examining the normalized field lines along various free parameters. Our findings indicate that the parameters $( R_0 )$ and $( f_ε = g_ε )$ influence the topological charges. These results are comprehensively summarized in Table I. In examining the photon sphere within this model, the sign of the parameter $ R_0 $ plays a crucial role in determining whether the model adopts a dS or AdS configuration. An interesting characteristic of this model is that, in its AdS form, it avoids the formation of naked singularity regions, which sets it apart from many other models. Typically, varying parameter values in other models can result in the division of space into regions of black holes and naked singularities. However, this model consistently retains its black hole behavior by featuring an unstable photon sphere, regardless of parameter values within the acceptable range. In its dS form, the behavior of the model's photon sphere remains consistent with other dS models and does not exhibit unique differences.

gr-qc↗

arXiv2025

Information Theoretical Approach to Detecting Quantum Gravitational Corrections

One way to test quantum gravitational corrections is through black hole physics. In this paper, We investigate the scales at which quantum gravitational corrections can be detected in a black hole using information theory. This is done by calculating the Kullback-Leibler divergence for the probability distributions obtained from the Parikh-Wilczek formalism. We observe that the quantum gravitational corrections increase the Kullback-Leibler divergence as the mass of the black hole decreases, which is expected as quantum gravitational corrections can be neglected for larger black holes. However, we further observe that after a certain critical value, quantum gravitational corrections tend to decrease again as the mass of the black hole decreases. To understand the reason behind this behavior, we explicitly obtain Fisher information about such quantum gravitational corrections and find that it also increases as the mass decreases, but again, after a critical value, it decreases. This is because at such a scale, quantum fluctuations dominate the system and we lose information about the system. We obtain these results for higher-dimensional black holes and observe this behavior for Kullback-Leibler divergence and Fisher information depending on the dimensions of the black hole. These results can quantify the scale dependence and dimension dependence of the difficulty in detecting quantum gravitational corrections.

hep-th↗

arXiv2024

Holographic Boundary Conformal Field Theory within Horndeski Gravity

We investigate entanglement islands and the Page curve in the framework of Horndeski gravity on a Karch-Randall braneworld background. In particular, treating the holographic boundary conformal field theory analytically we find that the Horndeski parameters significantly alter the behavior of the Page curve compared to standard general relativity, a feature caused by the nontrivial geometry induced by the Horndeski scalar field. Interestingly enough, the geometry far from the AdS limit plays a more significant role compared to previous studies. This suggests that Horndeski gravity introduces important modifications to the distribution of quantum information in the holographic model. Finally, we claim that holographic consistency can be used reversely to impose constraints on Horndeski gravity itself, providing a new tool for probing the validity of modified gravity theories.

hep-th↗

arXiv2024

Quantum gravitational corrections to the geometry of charged AdS black holes

We study the quantum gravitational corrections to the geometry of a four-dimensionalcharged (Reissner-Nordström) Anti de Sitter black hole starting from an effective field theory approach to quantum gravity. We use the expression of the modified horizon radius to compute the quantum corrected Wald entropy, whose expression reproduces the logarithmic behaviour found by other methods. We perform a thermodynamics analysis and compute the quantum gravitational corrections to the temperature, pressure, specific heat and Helmholtz free energy. All these quantities are renormalisation group invariant. We find that a quantum charged AdS black hole can exist only for a bounded range of masses and that it can undergo a second order phase transition as it moves from a state with positive specific heat to a negative one.

hep-th↗

arXiv2024

Thermodynamic Topology and Phase Space Analysis of AdS Black Holes Through Non-Extensive Entropy Perspectives

This paper studies the thermodynamic topology through the bulk-boundary and restricted phase space (RPS) frameworks. In bulk-boundary framework, we observe two topological charges $(ω= +1, -1)$ concerning the non-extensive Barrow parameter and with ($δ=0$) in Bekenstein-Hawking entropy. For Renyi entropy, different topological charges are observed depending on the value of the $λ$ with a notable transition from three topological charges $(ω= +1, -1, +1)$ to a single topological charge $(ω= +1)$ as $λ$ increases. Also, by setting $λ$ to zero results in two topological charges $(ω= +1, -1)$. Sharma-Mittal entropy exhibits three distinct ranges of topological charges influenced by the $α$ and $β$ with different classifications viz $β$ exceeds $α$, we will have $(ω= +1, -1, +1)$, $β= α$, we have $(ω= +1, -1)$ and for $α$ exceeds $β$ we face $(ω= -1)$. Also, Kaniadakis entropy shows variations in topological charges viz we observe $(ω= +1, -1)$ for any acceptable value of $K$, except when $K = 0$, where a single topological charge $(ω= -1)$. In the case of Tsallis-Cirto entropy, for small parameter $Δ$ values, we have $(ω= +1)$ and when $Δ$ increases to 0.9, we will have $(ω= +1, -1)$. When we extend our analysis to the RPS framework, we find that the topological charge consistently remains $(ω= +1)$ independent of the specific values of the free parameters for Renyi, Sharma-Mittal, and Tsallis-Cirto. Additionally, for Barrow entropy in RPS, the number of topological charges rises when $δ$ increases from 0 to 0.8. Finally for Kaniadakis entropy, at small values of $K$, we observe $(ω= +1)$. However, as the non-extensive parameter $K$ increases, we encounter different topological charges and classifications with $(ω= +1, -1)$.

hep-th↗

arXiv2024

Thermodynamic Topology, Photon Spheres, and Evidence for Weak Gravity Conjecture in Charged Black Holes with Perfect Fluid within Rastall Theory

In this paper, we explore the Weak Gravity Conjecture (WGC) within the context of photon spheres in charged black holes, framed by Perfect Fluid in Rastall Theory. We aim to validate the WGC by identifying the extremality states of these black holes. We highlight the interplay between quantum dynamics and gravitational forces, opening new avenues in high-energy physics and quantum gravity. Our analysis reveals significant system changes with varying perfect fluid intensity $(α)$ and Rastall parameters ( $k$ and $λ$ ). For dust field $(ω=0)$, the WGC is met in extremality $(T=0)$ with $(Q / M)_{\text {ext }}>1$, indicating a black hole due to the presence of photon spheres (PS) with a total charge-1. However, further increases in $k$ and $λ$ or decreases $(α)$ lead to $P S=0$ that determines a singularity, not a black hole. We observed that the radiation field $(ω=1 / 3)$, quintessence field ( $ω=-2 / 3$ ), and phantom fields field ( $ω=-4 / 3$ ) also confirmed the WGC and maintaining a total charge of $P S=-1$ in some regions of the free parameters. Our numerical solutions identify points satisfying the WGC, establishing a bridge between quantum and cosmic realms. The results are summarized in Table (I). We also examine Duans topological current $ϕ$-mapping theory by analyzing generalized Helmholtz free energy methods to study the topological classes of our black hole. We reveal that for given values of the free parameters, the total topological numbers $(W=0)$ exist for the generalized Helmholtz free energy method for $ω=0,1 / 3,-2 / 3,-4 / 3$.

hep-th↗

arXiv2024

Holographic Thermodynamics of an Enhanced Charged AdS Black Hole in String Theory's Playground

In this paper, we consider an $α^{\prime}$ corrected Reissner-Nordström AdS black hole to study thermodynamics. We study the $P-V$ criticality and thermodynamical stability of the black hole. We obtained a first-order phase transition, which may be interpreted as the large/small black hole phase transition. Therefore, we obtained a van der Waals behaviour and obtained critical points. Finally, we calculate quantum work used to resolve the information loss paradox.

hep-th↗

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

Unveiling the Fifth State of Matter: Insights into Ultra-Hot Plasma and its Applications

In this work, we investigate the dissociation energy of the North (N) and South (S) poles of a quantum magnetic particle, incorporated within both classical and quantum mechanical perspectives. A simple model of a harmonic oscillator is employed to estimate the dissociation energy of the N-S poles, as well as the corresponding breakdown temperature and internal pressure. The results indicate that the separation of magnetic poles occurs in two states: (a) in an ultra-hot plasma medium with extremely high temperatures, such as in the core of a hot star, and (b) at extremely high pressures, such as between internal plates in complex superlattices of layered solids. The breakdown temperature is found to be of the order of $10^7$ to $10^8$ Kelvin, which is only achievable in an ultra-hot plasma environment, known as the fifth phase of matter. Based on this model, the possibility of dissociation of bonds between N and S magnetic poles for solid superlattices under very high pressures between crystal plates is also calculated. The results suggest that the presence of isolated magnetic monopoles in superlattices of solids under ultra-high-pressure conditions is possible. Consequently, the model proposes that the conductivity of magnetic monopole carriers can be applied to the manipulation of nanomaterials for the production of advanced devices, such as new generations of superconductors, new spin devices, and magnetic-electronics, advanced materials with magnetic monopoles, as well as super-dielectrics.

physics.plasm-ph↗

arXiv2024

de Sitter versus anti-de Sitter in Horndeski-like gravity

We present general solutions of Horndeski-like gravity that can interpolate between the de Sitter and anti-de Sitter regimes. In particular, we develop the first-order formalism with two scalar fields, and considering a black hole ansatz with flat slicing we investigate three different cases, namely exponential, vacuum, and smooth superpotential solutions, with no Minkowski extrema. Furthermore, with these solutions we show that a Renormalization Group flow is established, and we obtain a turnaround in the warp factor, where the transition is bounded by the area low. We discuss the ideal regimes to trap gravity, which are constructed using the holographic function, which provides stable and unstable regimes to localize gravity. Finally, we show that no ghost appear and that the matter sector that violates the $c$-theorem is physical.

hep-th↗

arXiv2024

Thermal fluctuations of (non)linearly charged BTZ black hole in massive gravity

We consider a charged BTZ black hole in asymptotically AdS space-time of massive gravity to study the effect of the thermal fluctuations on the black hole thermodynamics. We consider the Einstein-Born-Infeld solution and investigate critical points and stability. We also compare the results with the case of Einstein-Maxwell solutions. Besides, we find that thermal fluctuations, which appear as a logarithmic term in the entropy, affect the stability of the black hole and change the phase transition point. Moreover, we study the geometrical thermodynamics and find that the behaviour of the linear Maxwell solution is the same as the nonlinear one.

gr-qc↗

arXiv2023

Exploring Non-perturbative Corrections in Thermodynamics of Static Dirty Black Holes

This study presents an investigation into the thermodynamic properties of a dirty black hole immersed in a uniform electric field within the framework of the Einstein-Nonlinear Electrodynamics (ENE)-dilaton theory. The analysis delves into various thermodynamic aspects, including heat capacity, Helmholtz free energy, and internal energy, providing insights into the behavior of the black hole under the influence of the electric field. Furthermore, the article explores the intricate interplay between quantum effects and thermodynamic behavior through the examination of quantum-corrected entropy. The study aims to shed light on the non-perturbative corrections that arise in this complex system, offering a comprehensive understanding of the modified thermodynamics of dirty black holes within the specified theoretical framework.

hep-th↗

arXiv2023

Thermodynamic schemes of charged BTZ-like black holes in arbitrary dimensions

We investigate thermodynamic schemes of charged BTZ-like black holes in arbitrary dimensions, namely higher-dimensional charged black holes in which the electromagnetic sector exhibits the same properties with that of the usual three-dimensional BTZ solution. We first present the Euclidean on-shell action in arbitrary dimensions, inserting a radial cutoff. We then extract the corresponding thermodynamic quantities from the semi-classical partition function in different ensembles and find that there exist two possible thermodynamic schemes, with different outcomes. Regarding the traditional scheme (scheme I), where the length cutoff is identified with the AdS radius, we show that charged BTZ-like black holes are super-entropic, namely they violate the reverse isoperimetric inequality conjecture, and their super-entropicity is strongly connected to a fundamental thermodynamic instability. This class of solutions is the first demonstration of super-entropic black holes which possess second-order critical points and, since thermodynamic instabilities always arise, it is not possible to physically interpret the corresponding van der Waals critical phenomenon in this scheme. In the second scheme (II) where the length cutoff is considered as an independent variable, namely the system respects the conjectured reverse isoperimetric inequality, we show that the solutions are thermodynamically stable in an ensemble where the length cutoff is kept fixed, and hence one can provide an explanation for the van der Waals critical phenomenon. Furthermore, in order to verify the consistency of the second scheme, we study the Joule-Thomson expansion and we extract the Joule-Thomson coefficient, the inversion temperature, the inversion curves, and the isenthalpic curves. The results indicate that this class of AdS black holes can be considered as interacting statistical systems. Additionally, ...

hep-th↗

arXiv2023

Superradiant (In)stability, Greybody Radiation, and Quasinormal Modes of Rotating Black Holes in non-linear Maxwell f (R) Gravity

The research of superradiant instability in the realm of quantum gravity is a well-known topic, with many physicists and astronomers studying the potential impact it can have on gravitational waves, the structure of the universe, and spacetime itself. In this work, we investigate the superradiant (in)stability of a rotating black hole obtained from the nonlinear Maxwell $f(R)$ gravity theory. In this study, the evaluation of stability/instability is going to be based on non-existence and existence of magnetic field, when the magnetic field constant becomes $c_{4}=0$ and $c_{4}\neq 0$, respectively. The analyzes of greybody factor (GF) and quasinormal modes (QNMs) are investigated in the stationary black hole spacetime both in the absence and presence of the magnetic field parameter. To this end, we first consider the Klein-Gordon equation for the complex scalar field in the geometry of that rotating black hole. In the sequel, the obtained radial equation is reduced to a one-dimensional Schrödinger-like wave equation with an effective potential energy. The effects of the nonlinear Maxwell $f(R)$ gravity theory parameters ($q$, $c$, and $c_{4}$) on the effective potential, GFs, and QNMs are thoroughly investigated. The obtained results show that even though the factors $q$, $c$, and $c_{4}$ all affect the effective potential, this phenomena, surprisingly, is not valid for the GFs and QNMs. With the proper graphics and tables, all outputs are depicted, tabulated, and interpreted.

hep-th↗