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Saheb Soroushfar

Publications and source records attributed to Saheb Soroushfar.

At least 19 recordsLinked to original sources

Static Magnetic Brane Solutions in Quartic Quasi-Topological Gravity with Power-Law Maxwell Nonlinear Electrodynamics

In this paper, we derive static magnetic brane solutions in quasi-topological gravity, considering the presence of power-law Maxwell nonlinear electrodynamics. The resulting solutions are horizonless and curvature-free. However, there exists a conic singularity with a deficit angle, which depends solely on the parameters $q$, $n$, and $s$ (where $s$ is the nonlinear parameter). In addition, in order to obtain finite solutions at infinity, the parameter $s$ of the power-law Maxwell theory is constrained to the range $1/2 < s \leq 2$. It is also observed that, for $\rho$ approaching $r_+$, the solutions $f(\rho)$ are dependent on the values of parameters $q$ and $n$, and for larger values of $\rho$, the solutions depend on the coefficients of Lovelock and quasi-topological gravities, namely $\lambda$, $\mu$, and $c$. Finally, we employ the counterterm method to compute the conserved quantities of these spacetimes.

gr-qc

Quantum-corrected thermodynamics of Schwarzschild AdS black holes in conformal Killing gravity

We study Schwarzschild--AdS black holes in conformal Killing gravity with non-perturbative entropy corrections within the extended phase-space formalism. By deriving the quantum-corrected heat capacity, Helmholtz free energy, internal energy, and Gibbs free energy, we show that quantum corrections modify phase transition points and thermal stability mainly at small horizon radii, while classical behavior is recovered for large black holes. Critical behavior of van der Waals type appears exclusively for positive values of the conformal Killing parameter $a$. Applying the island prescription, we find that the entanglement entropy of Hawking radiation saturates after the Page time at $S_{\text{sat}} = 2(\pi r_H^2 + \eta e^{-\pi r_H^2})$, thereby restoring unitarity. Stronger quantum corrections increase the entropy threshold and delay information recovery. Furthermore, we examine the universal thermodynamic relation in the extremal limit under a minimal perturbation of the AdS curvature radius. We prove that the quantum correction parameter $\eta$ cancels out completely, yielding the robust universal combination $U = -r_{\text{ext}}^3 / l^3$. This demonstrates that the universal relation remains stable against non-perturbative quantum corrections to the entropy.

gr-qc

Holographic CFT Thermodynamics as a Bridge Between the Weak Gravity and Weak Cosmic Censorship Conjectures for EMPYM--AdS Black Holes

The weak cosmic censorship conjecture (\WCCC) and the weak gravity conjecture (\WGC) sit at the heart of how singularities and charged matter are constrained in any consistent theory of quantum gravity. We study both conjectures for Einstein--Maxwell--power--Yang--Mills--AdS (\EMPYM) black holes, a family in which a non-Abelian power-law Yang--Mills field, a Maxwell field, and a negative cosmological constant act together. Working in holographic conformal field theory (CFT) thermodynamics, we treat the central charge $C$ and the CFT volume $\Vol$ as independent variables and obtain an extended first law that carries variations of the Yang--Mills charge and of the nonlinearity exponent $\gamma$. A closed Euler relation follows, and we check it together with the full set of equations of state to machine precision. The perturbation is a charged massive scalar minimally coupled to the Maxwell sector. Its horizon energy and charge fluxes fix the superradiance threshold $\omega<\tilde{q}_s\tilde{\phi}_h$, and the mass--energy relation $\mu_s=\omega$ turns this into the bound $\tilde{q}_s/\mu_s>r_{\min}/\tilde{Q}$. Expanding the metric function $f(r)$ about its minimum for extremal and near-extremal configurations, we find that absorption keeps $f_{\min}$ non-positive, so the horizon survives. The Yang--Mills sector lowers the effective charge-to-mass threshold below the Reissner--Nordstr\"om value of unity, while a local stability analysis locates a Davies point in the heat capacity. Across the parameter range examined the \EMPYM\ family respects cosmic censorship under scalar perturbations, with the \WGC\ fixing only the direction of evolution toward or away from extremality.

hep-th

Thermodynamic analysis of a compact object in Rastall-Rainbow gravity

In this paper, we investigate the thermodynamic behavior of a horizonless compact object within the framework of Rastall-Rainbow (RR) gravity. Working with local shell thermodynamics for gravastar and an exterior fiducial temperature, we show that the RR modification bends temperature to produce two extrema and a stable mass remnant at zero temperature. We show that the gravastar's shell entropy is smaller than that of a comparable black hole, and that RR modifications introduce a logarithmic correction which contributes to specific heat positivity and a smoother free energy landscape of small gravastars. A Central finding of this work is that, from heat capacity and Helmholtz free energy analyses, we uncover small, middle, and large branches and demonstrate that unlike Rainbow modified black holes, the small RR gravastar is both locally and globally favored over hot curved space. At the parameter level, both Rastall and Rainbow play distinct roles. Increasing the Rastall parameter, by strengthening matter-curvature coupling, adjusts the redshift between the shell and the exterior, shifts the temperature maximum to higher values at larger masses, and narrows the unstable window. In contrast, increasing the Rainbow parameter enhances energy dependent UV suppression and bends the temperature in lower values at larger masses. Altogether, these results highlight a controlled route to thermodynamic stabilization and the emergence of a stable remnant in horizonless compact objects within RR gravity.

gr-qc

A Brief Review of Quantum Tunneling: Computational Approaches and Experimental Evidence

This paper presents a concise review of the quantum tunneling approach to Hawking radiation, covering its theoretical foundations, extensions, and experimental efforts. We begin by outlining the Hamilton-Jacobi and Parikh-Wilczek methods, which provide a semi-classical framework for deriving Hawking radiation from stationary black holes. The discussion is then extended to dynamical black holes, where evolving horizons require modified treatments incorporating trapping horizons, Kodama vectors, and dynamical surface gravity. We explored the possible tunneling paths for particles crossing the horizon in dynamical black holes and emphasized the crucial role of the imaginary part of the action in determining the Hawking temperature. In the second part, we review experimental investigations of Hawking radiation, including analogue black hole experiments, quantum simulations, and astrophysical searches for primordial black hole evaporation. While no direct detection of Hawking radiation has been achieved, recent advances in Bose-Einstein condensates, optical analogues, and superconducting qubits offer indirect support for the tunneling interpretation of black hole evaporation.

gr-qc

History of a Particle Bounded to the Cosmological LTB Black Hole Surrounded by the Quintom Field

In this paper, we derived the complete set of time-dependent geodesic equations for an LTB black hole surrounded by a Quintom field and investigated the evolution of effective potential and photon orbits across cosmic epochs. Our findings demonstrate that in an accelerated universe, the peak of an effective potential decreases in height and shifts toward smaller radii. Additionally, the probability of stable orbit formation decreases as cosmic expansion progresses. We classified the possible trajectories into four types: terminating bound orbits, stable orbits, scattering flyby orbits, and terminating escape orbits. The results indicate that stable bound orbits are more prevalent in the early universe, whereas at late time epochs, flyby orbits become dominant due to the expansion-driven weakening of gravitational potential. We further analyzed the impact of angular momentum on the evolution of orbits, showing that as it increases, the ISCO radius decreases while the peak of the effective potential shifts outward. This suggests that particles with higher angular momentum follow extended bound orbits, and more energetic photons are more likely to be captured by the black hole. Conversely, an increase in angular momentum reduces the probability of flyby orbits while increasing the likelihood of direct fall into the black hole. Our study provides new insights into how cosmic acceleration influences black hole geodesics, revealing that the progressive shrinking of ISCO and stable orbits eventually disappear as the universe approaches the Big Rip singularity. These findings contribute to a deeper understanding of the dynamical nature of cosmological black holes and may offer new perspectives for observational tests through gravitational lensing, accretion disk evolution, and quasi-periodic oscillations (QPOs) in evolving black hole spacetimes.

gr-qc

Non-perturbative correction to thermodynamics of conformally dressed 3D black hole

We extend the study of corrected thermodynamics for the 3D black holes conformally coupled to scalar field up to non-perturbative level. We calculate the exponential correction to entropy arises due to the microstate counting for quantum states on the boundary. This exponential correction in entropy attributes to the other thermodynamical quantities also. We study the stability and phase transition for this system of black hole under the influence of non-perturbative correction. We also discuss the quantum work associated with exponential corrected entropy. Finally, we justify the results from the view point of thermodynamic geometry.

gr-qc

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

Astrophysical and electromagnetic emissivity properties of black holes surrounded by a quintessence type exotic fluid in the Scalar-Vector-Tensor Modified Gravity

The astrophysical consequences of the presence of a quintessence scalar field on the evolution of the horizon and on the accretion disk surrounding a static black hole, in the Scalar-Vector-Tensor version of Modified Gravity (MOG), are investigated. The positions of the stable circular orbits of the massive test particles, moving around the central object, are obtained from the extremum of the effective potential. Detailed calculations are also presented to investigate the light deflection, shadow and Shapiro effect for such a black hole. The electromagnetic properties of the accretion disks that form around such black holes are considered in detail. The energy flux and efficiency parameter are estimated analytically and numerically. A comparison with the disk properties in Schwarzschild geometry is also performed. The quantum properties of the black hole are also considered, and the Hawking temperature and the mass loss rate due to the Hawking radiation are considered. The obtained results may lead to the possibility of direct astrophysical tests of black hole type objects in modified gravity theories.

gr-qc

Quantum Thermodynamics of an M2-M5 Brane System

We will investigate a system of M2-M5 branes as a black M2-M5 bound state. The behavior of this system will be investigated at short distances. At such scales, we will have to incorporate quantum gravitational corrections to the supergravity solutions. We will study the non-equilibrium quantum thermodynamics of this black M2-M5 bound state. The quantum work for this solution will be obtained using the Jarzynski equality. We will also study the corrections to the thermodynamic stability of this system from quantum gravitational corrections. We will use the concept of a novel quantum mass to analyze the quantum gravitational corrections to the information geometry of this system. This will be done using effective quantum metrics for this system.

hep-th

Thermodynamic geometry of static and rotating regular black holes in conformal massive gravity

A version of massive gravity, namely conformal massive gravity, is employed to study the behavior of thermodynamic geometry for both the static and the rotating regular black holes. Whereas in thermodynamic geometry singularity can be interpreted as the second phase transition, seeing such phenomena as heat capacity behavior for both cases is investigated in detail. In addition, other thermodynamic quantities like the entropy and the temperature are analyzed as well. Another important property of the black holes is the so-called stability, in which utilizing the first phase transition of the heat capacity is detailed, for both cases, say the static and the spinning black holes. It is also interestingly figured out that, the behavior of temperature of the uncharged black holes in the presence of hair parameter, $λ$, can mimic the charged ones. {The effects of scalar charge, $Q$, and hair parameters with both positive and negative signs and how it affects key parameters in the study of black holes are investigated as well.} To investigate the properties of the black holes both regular thermodynamics and thermodynamic geometry approaches are considered. Then one can observe that aiming to realize the physics of the black holes, many complicated phenomena can be analyzed dramatically easier by considering the latter approach.

gr-qc

Quantum Work and Information Geometry of a Quantum Myers-Perry Black Hole

In this paper, we will obtain quantum work for a quantum scale five dimensional Myers-Perry black hole. Unlike heat represented by Hawking radiation, the quantum work is represented by a unitary information preserving process, and becomes important for black holes only at small quantum scales. It will be observed that at such short distances, the quantum work will be corrected by non-perturbative quantum gravitational corrections. We will use the Jarzynski equality to obtain this quantum work modified by non-perturbative quantum gravitational corrections. These non-perturbative corrections will also modify the stability of a quantum Myers-Perry black hole. We will define a quantum corrected information geometry by incorporating the non-perturbative quantum corrections in the information geometry of a Myers-Perry black hole. We will use several different quantum corrected effective information metrics to analyze the stability of a quantum Myers-Perry black hole.

hep-th

Perturbed thermodynamics and thermodynamic geometry of a static black hole in $f (R)$ gravity

In this paper, we consider a static black hole in $f(R)$ gravity. We recapitulate the expression for corrected thermodynamic entropy of this black hole due to small fluctuations around equilibrium. Also, we study the geometrothermodynamics (GTD) of this black hole and investigate the adaptability of the curvature scalar of geothermodynamic methods with phase transition points of this black hole. Moreover, we study the effect of correction parameter on thermodynamic behaviour of this black hole. We observe that the singular point of the curvature scalar of Ruppeiner metric coincides completely with zero point of the heat capacity and the deviation occurs with increasing correction parameter.

gr-qc

Geodesic Motion in the Spacetime Of a SU(2)-Colored (A)dS Black Hole in Conformal Gravity

In this paper, we study the geodesic motion in the spacetime of a SU(2)-colored (A)dS black hole in conformal gravity, and also we investigate spacetime features, such as light spheres and horizons. Moreover, we derive the analytical solutions for the equation of motion of test particles and light rays using Weierstrass elliptic and Kleinian sigma functions. Depending on the particle energy levels and angular momentums, we classify the solutions of the geodesic equations. Furthermore, several examples of possible types of orbits illustrate the results

gr-qc

Inflation in String Field Theory

In this paper, we analyze the inflationary cosmology using string field theory. This is done by using the zero level contribution from string field theory, which is a non-local tachyonic action. We will use the non-local Friedmann equations for this model based on string field theory, and calculate the slow-roll parameters for this model. We will then explicitly obtain the scalar and tensorial power spectrum, their related indices, and the tensor-to-scalar ratio for this model. Finally, we use cosmological data from Planck 2013 to 2018 to constrain the free parameters in this model and find that string field theory is compatible with them.

hep-th

Particle Dynamics Around the Black String

In this paper, some dynamical properties of neutral and charged particles around a weakly magnetized five-dimensional static black string have been studied. The perturbation method was also used to calculate the Innermost Stable Circular Orbit (ISCO) of this metric in the presence of a magnetic field. The escape velocity of neutral and charged particles around the black string was derived. In the next step, the analytical solutions of the equations of motion were discussed and some possible orbits for particles in the black string space-time were plotted. Interestingly, it was found that adding an extra dimension has a slight influence on the effective potential and one term of the effective force. The magnitude of the new constant of motion $(J)$ affects both the shape of the potential and existence of the stable circular orbits. In conclusion, by comparing a black hole and a black string, it is realized that the value of a new constant of motion causes slight but interesting differences.

gr-qc

Phase transition of a charged AdS black hole with a global monopole through geometrical thermodynamics

In order to study the phase transition through thermodynamic geometry, we consider the charged AdS black hole with global monopole. We first introduce thermodynamics of charged AdS black hole with global monopole by discussing the dependence of Hawking temperature, specific heat and P-v curve on horizon radius and monopole parameter. By implementing various thermodynamic geometry methods, for instance, Weinhold, Ruppiner, Quevedo and HPEM formulations, we derive corresponding scalar curvatures for charged AdS black hole with a global monopole. Here, we observe that, in contrast to Weinhold and Ruppeiner methods, HPEM and Quevedo formulations provide more information about the phase transition of the charged AdS black hole with a global monopole.

gr-qc

Accretion disks around a static black hole in $f(R)$ gravity

We provide a description of a thin accretion disc for a static spherically symmetric black holes in $f(R)$ gravity. In this regard, we first study the horizons of black holes in $f(R)$ gravity. The equation of motion and effective potential are also computed which eventually leads to possible existence of innermost circular orbits of accretion disc. We derive the specific energy, specific angular momentum and angular velocity of the particles moving in circular orbits also. A comparative study of various parameters are also presented. The locations of the event horizon, cosmological horizon, innermost and outermost stable circular orbits are also pointed out.

gr-qc