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Mohammad Ali S. Afshar

Publications and source records attributed to Mohammad Ali S. Afshar.

At least 37 records · Page 2Linked to original sources

Kramer's Escape Rate and Phase Transition Dynamics in AdS Black Holes

Traditional static methods in phase transition studies, provide good insights into the thermodynamics of black holes. However, they practically lose sight of the dynamic aspects and temporal sequence of events. The Kramer's escape rate, central to our research, offers a somewhat dynamic approach to phase transition. We examine the free energy landscapes for black holes under the influence of 'dark' and 'stringy dark' structures, assessing how additional parameters affect the escape rates and dynamics of the transition during the first-order phase transition from small to large black holes. In our analysis, we consider the escape rate as a function of the black hole radius and study its variations. We will observe that, on one hand, the escape rate well represents our assumption based on the movement from zero, increasing to a maximum point, and then decreasing back to zero as reactive structures become active during the phase transition interval. However, the critical point in this method is the encounter with a specific and distinct point. This is where the diagram of the direct process (escape rate from small to large black holes) intersects with the reverse process (large to small black holes), becoming equally probable (contact point). The point, which seems improbable at the onset of the phase transition or very negligible, gains more significance as the process progresses. This increase indicates the dominance of a region where the escape rate from larger black holes to smaller ones prevails. The predominance of the reverse process, which increases as we approach the end of the process and is necessarily accompanied by a variation in radius, may be considered as a natural reaction of the black hole against the 'phase change' action. A reaction which attempting to prevent any uncontrolled radial growth that could jeopardize the stability of the black hole.

gr-qc↗

WGC as WCCC protector: The Synergistic Effects of various Parameters in Identifying WGC candidate Models

The integration of non-commutative geometry and Gauss-Bonnet corrections in an action and the study of their black hole responses can provide highly intriguing insights. Our primary motivation for this study is to understand the interplay of these two parameters on the geodesics of spacetime, including photon spheres and time-like orbits. In this study, we found that this integration, in its initial form, can limit the value of the Gauss-Bonnet parameter ($α$), creating a critical threshold beyond which changes in the non-commutative parameter ($Ξ$) become ineffective, and the structure can only manifest as a naked singularity. Furthermore, we found that using a more complex model, which includes additional factors such as a cloud of strings and linear charge, as a sample for studying spacetime geodesics, yield different and varied results. In this scenario, negative $α$ values can also play a role, notably preserving the black hole form even with a super-extremal charge ($q > m$). For $α> 0.1$, the black hole mass parameter becomes significantly influential, with a critical mass below which the impact of other parameter changes is nullified. Interestingly, considering a more massive black hole, this high-mass state also maintains its black hole form within the super-extremal charge range. The existence of these two models led us to our main goal. By examining the temperature for these two cases, we find that both situations are suitable for studying the WGC. Finally, based on the behavior of these two models, we will explain how the WGC acts as a logical solution and a protector for the WCCC.

physics.gen-ph↗

Topological Insights into Black Hole Thermodynamics: Non-Extensive Entropy in CFT framework

In this paper, We conducted an in-depth investigation into the thermodynamic topology of Einstein-Gauss-Bonnet black holes within the framework of Conformal Field Theory (CFT), considering the implications of non-extensive entropy formulations. Our study reveals that the parameter $λ$ (Rényi entropy) plays a crucial role in the phase behavior of black holes. Specifically, when $λ$ is below the critical value (C), it has a negligible impact on the phase behavior. However, when $λ$ exceeds the critical value, it significantly alters the phase transition outcomes. Determining the most physically representative values of $λ$ will require experimental validation, but this parameter flexibility allows researchers to better explain black hole phase transitions under varying physical conditions. Furthermore, the parameters $α$ and $β$ affect the phase structure and topological charge for the Sharma-Mittal entropy. Only in the case of $C>C_c$ and in the condition of $α\approxβ$ will we have a first-order phase transition with topological charge + 1. Additionally, for the loop quantum gravity non-extensive entropy as the parameter $q$ approaches 1, the classification of topological charges changes. We observe configurations with one and three topological charges with respect to critical value $C$, resulting in a total topological charge $W = +1$, and configurations with two topological charges $(ω= +1, -1)$, leading to a total topological charge $W = 0$. These findings provide new insights into the complex phase behavior and topological characteristics of black holes in the context of CFT and non-extensive entropy formulations.

gr-qc↗

Effective Potential and Topological Photon Spheres: A Novel Approach to Black Hole Parameter Classification

In this paper, we base our analysis on the assumption that the existence of a photon sphere is an intrinsic feature of any ultra-compact gravitational structure with spherical symmetry. Utilizing the concept of a topological photon sphere, we categorize the behaviors of various gravitational models based on the structure of their photon spheres. This innovative approach enables us to define boundaries for black hole parameters, subsequently allowing us to classify the model as either a black hole or a naked singularity. Indeed, we will demonstrate that the presence of this interplay between the gravitational structure and the existence of a photon sphere is a unique advantage that can be utilized from both perspectives. Our observations indicate that a gravitational model typically exhibits the behavior of a horizonless structure (or a naked singularity) when a minimum effective potential (a stable photon sphere) appears within the studied spacetime region. Additionally, in this study, we tried to investigate the effect of this structure on the behavior of the photon sphere by choosing models that are affected by the Perfect Fluid Dark Matter (PFDM). Finally, by analyzing a model with multiple event horizons, we show that the proposed method remains applicable even in such scenarios.

gr-qc↗

Mutual Influence of Photon Sphere and Non-Commutative Parameter in Various Non-Commutative Black Holes: Part I- Towards evidence for WGC

Non-commutative black holes(NCBH), due to the non-commutativity of spacetime coordinates, lead to a modification of the spacetime metric. By replacing the Dirac delta function with a Gaussian distribution, the mass is effectively smeared, eliminating point-like singularities. Our objective is to investigate the impact of this change on spacetime geodesics, including photon spheres and time-like orbits. We will demonstrate how the photon sphere can serve as a tool to classify spacetime, illustrating the influence of the NC parameter and constraining its values in various modes of these black holes. Additionally, using this classification, we will show how the addition of the nonlinear Einstein-Born-Infeld(BI) field to the model enhances its physical alignment with reality compared to the charged model. In the dS BI model, we will show how the study of the effective potential and photon sphere can provide insights into the initial structural status of the model, thereby establishing this potential as an effective tool for examining the initial conditions of black holes. Finally, by examining super-extremality conditions, we will show that the AdS BI model, with the necessary conditions, can be a suitable candidate for studying and observing the effects of the Weak Gravity Conjecture (WGC).

gr-qc↗

Weak Cosmic Censorship and Weak Gravity Conjectures in CFT Thermodynamics

In this paper, we explore the intriguing interplay between fundamental theoretical physics concepts within the context of charged black holes. Specifically, we focus on the consistency of the weak gravity conjecture (WGC) and weak cosmic censorship conjecture (WCCC) in the thermodynamics of conformal field theory (CFT), and restricted phase space thermodynamics (RPST) for AdS Reissner-Nordstrom black holes with a perfect fluid dark matter (RN-PFDM). The WGC ensures that gravity remains the weakest force in the system. Meanwhile, the WCCC addresses the cosmic censorship problem by preventing the violation of fundamental physical laws near the black hole singularity. First, we analyze the RN black hole's free energy in both spaces, revealing a distinctive swallowtail pattern indicative of a first-order phase transition when certain free parameter conditions are met. We explore the WGC across different phase spaces, emphasizing the need for certain conditions in extended phase space thermodynamics (EPST), RPST, and CFT. We demonstrate that PFDM parameter \( γ\) and the radius of AdS \( l \) have a vital role in proving the satisfaction of the WGC. Also, these values have a linear relation with the range compatibility of WGC. The range of compatibility for WGC in RPST and EPST is the same while for CFT, this range is larger than EPST, and RPST. It means somehow the WGC and CFT are more consistent. The WCCC was examined at the critical juncture, confirming its validity in critical points. We conclude that the WGC is supported at the critical point of black holes, and the WCCC is also maintained, demonstrating the robustness of these conjectures within the critical ranges of black hole parameters

hep-th↗

Analyzing WGC and WCCC through Charged Scalar Fields Fluxes with Charged AdS Black Holes Surrounded by Perfect Fluid Dark Matter in the CFT Thermodynamics

In this paper, we conduct a comprehensive investigation into the weak cosmic censorship conjecture (WCCC) for Reissner-Nordström (R-N) AdS black holes that are influenced by Perfect Fluid Dark Matter (PFDM). Our study is framed within the context of Conformal Field Theory (CFT) thermodynamics. We delve into the principles of energy flux and mass-energy equivalence to explore the interplay between the weak gravity conjecture (WGC) and the WCCC. Our analysis begins by examining the interaction between incoming and outgoing energy fluxes, which induces changes in the black hole's properties. By applying the first law of thermodynamics, we assess the validity of the second law in these dynamic scenarios. We also consider equilibrium conditions that involve both absorption and superradiance processes. Utilizing the framework of black hole thermodynamics within CFT, we demonstrate that the WCCC is upheld if the black hole is in or near an extremal state, particularly when it is subjected to radiation and particle absorption. This finding is significant as it reinforces the robustness of the WCCC under these specific conditions. Furthermore, we uncover additional insights by employing mass-energy equivalence principles and conducting second-order approximations near the extremality state. Specifically, we find that when a black hole radiates and its central charge surpasses the scaled electric charge, the emitted superradiant particles adhere to the WGC. This adherence results in the black hole moving away from its extremal state, thereby maintaining the WCCC.

hep-th↗

Weak Gravity Conjecture Validation with Photon Spheres of Quantum Corrected AdS-Reissner-Nordstrom Black Holes in Kiselev Spacetime

In this study, we investigate the Weak Gravity Conjecture (WGC) in the context of quantum-corrected AdS-Reissner-Nordstrom (AdS-RN) black holes within Kiselev spacetime. Our focus is on photon spheres, which serve as markers for stable and unstable photon spheres. We confirm the validity of the WGC by demonstrating that quantum corrections do not alter the essential charge-to-mass ratio, thereby supporting the conjecture's universality. Our analysis reveals that black holes with a charge greater than their mass ($Q > M$) possess photon spheres or exhibit a total topological charge of the photon sphere (PS = -1), which upholds the WGC. This finding is significant as it reinforces the conjecture's applicability even in the presence of quantum corrections. Furthermore, we examine various parameter configurations to understand their impact on the WGC. Specifically, we find that configurations with $ω= -\frac{1}{3}$ and $ω= -1$ maintain the conjecture, indicating that these values do not disrupt the charge-to-mass ratio required by the WGC. However, for $ω= -\frac{4}{3}$, the conjecture does not hold, suggesting that this particular parameter value leads to deviations from the expected behavior. These results open new directions for research in quantum gravity, as they highlight the importance of specific parameter values in maintaining the WGC. The findings suggest that while the WGC is robust under certain conditions, there are scenarios where it may be challenged, prompting further investigation into the underlying principles of quantum gravity

gr-qc↗

The interplay of WGC and WCCC via charged scalar field fluxes in the RPST framework

In this paper, we investigate the weak cosmic censorship conjecture (WCCC) for the Reissner-Nordstrom (R-N) AdS black hole in a restricted phase space thermodynamics (RPST). Also here, we consider energy flux and equivalence mass-energy principle and examine the weak gravity conjecture (WGC) and the weak cosmic censorship conjecture. The incoming and outgoing energy flux leads to changes in the black hole. In that case, by applying the first law, we examined whether the second law of thermodynamics is valid. And also one can say that, in the case where absorption and superradiance are in the saturated to an equilibrium. Also, by using the thermodynamics of black holes in the restricted phase space, we show that if the black hole is in an extreme or close to an extreme state with radiation and particle absorption, the weak cosmic censorship conjecture is established. In addition, with the help of equivalence mass and energy principle and second-order approximation, in the near extremity, we find that when the black hole radiates and its central charge is greater than the scaled electric charge, the superradiance particles obey the weak gravity conjecture, and this causes the black hole to move further away from its extreme state. But when the particles that obey the weak gravity conjecture are attracted to the black hole when the black hole is very small. Then, in this case, we note that the black hole becomes closer to its extreme state.

hep-th↗

Exploring the Parameter Space of Inflation Model on the Brane and its Compatibility with the Swampland Conjectures

In recent years, inflationary models have been studied from different perspectives using different conditions. Now, in this paper, we want to investigate the inverse monomial Inflation $(IMI)$ on the brane. We limit our results to the potentials of the form $\frac{M^{4+σ}}{ϕ^σ}$. We calculate some cosmological parameters and then we investigate the satisfaction of the model with some conjectures of the swampland program. We will check the model's compatibility with the refined dS swampland conjecture(RDSSC), further refining the de Sitter swampland conjecture (FRSDC), scalar weak gravity (SWGC), and strong scalar weak gravity conjecture (SSWGC). Despite the incompatibility with (DSSC), We find a specific region of compatibility with other ones which means it satisfied the (FRDSSC) for example with (a=0.982873, b=0.017127, q=2.2). Also, the model is compatible with the (SWGC) with the ($ϕ\leq σ+2$) condition and consistent with the (SSWGC) with the ($ϕ\leq \sqrt{(σ+2)(σ+1)}$) condition. Since inverse monomial Inflation(IMI) on the brane could satisfy some swampland conjecture simultaneously, it has the potential to be a "real" inflation model of the universe.

gr-qc↗

Thermodynamic Topology of Quantum Corrected AdS-Reissner-Nordstrom Black Holes in Kiselev Spacetime

In this paper, we delve into the intricate thermodynamic topology of quantum-corrected Anti-de Sitter-Reissner-Nordstrm (AdS-RN) black hole within the framework of Kiselev spacetime. By employing the generalized off-shell Helmholtz free energy approach, we meticulously compute the thermodynamic topology of these selected black holes. Furthermore, we establish their topological classifications. Our findings reveal that quantum correction terms influence the topological charges of black holes in Kiselev spacetime, leading to novel insights into topological classifications. Our research findings elucidate that, in contrast to the scenario in which $ω=0$ and $a=0.7$ with total topological charge $W=0$ and $ω=-4/3$ with total topological charge $W=-1$, in other cases, the total topological charge for the black hole under consideration predominantly stabilizes at +1. This stabilization occurs with the significant influence of the parameters a, c, and $ω$ on the number of topological charges. Specifically, when $ω$ assumes the values of $ω=-1/3$, $ω=-2/3$ , $ω=-1$, the total topological charge consistently be to W = +1.

gr-qc↗

Exploring the Phase Transition in Charged Gauss-Bonnet Black Holes: A Holographic Thermodynamics Perspectives

In this paper, we delve into the study of thermodynamics and phase transition of charged Gauss-Bonnet black holes within the context of anti-de Sitter (AdS) space, with particular emphasis on the central charge's role within the dual conformal field theory (CFT). We employ a holographic methodology that interprets the cosmological constant and the Newton constant as thermodynamic variables, leading to the derivation of a modified first law of thermodynamics that incorporates the thermodynamic volume and pressure. Our findings reveal that the central charge of the CFT is intrinsically linked to the variation of these constants, and its stability can be ensured by simultaneous adjustment of these constants. We further explore the phase structures of the black holes, utilizing the free energy. Our research uncovers the existence of a critical value of the central charge, beyond which the phase diagram displays a first-order phase transition between small and large black holes. We also delve into the implications of our findings on the complexity of the CFT. Our conclusions underscore the significant role of the central charge in the holographic thermodynamics and phase transition of charged Gauss-Bonnet black holes. Furthermore, we conclude that while the central charge considered provides suitable and satisfactory solutions for this black hole in 4 and 5 dimensions, it becomes necessary to introduce a unique central charge for this structure of modified gravity. In essence, the central charge in holographic thermodynamics is not a universal value and requires modification in accordance with different modified gravities. Consequently, the physics of the problem will significantly deviate from the one discussed in this article, indicating a rich and complex landscape for future work.

gr-qc↗

Phase Transition Dynamics of Black Holes Influenced by Kaniadakis and Barrow Statistics

In this study, we investigate the dynamics and frame-by-frame phase transition of the first order in black hole thermodynamics. For our analysis, we will utilize the Kramers escape rate. Our focus is on charged anti-de Sitter (AdS) black holes influenced by Kaniadakis and Barrow statistics. The selection of these black holes aims to examine the effects of entropy variation on the dynamics of phase transition and to demonstrate that the Kramers escape rate, as an efficient tool, can effectively represent the dynamic transition from a small to a large black hole within the domain of first-order phase transitions. It is noteworthy that while the transition from small to large black holes should ostensibly dominate the entire process, our results indicate that the escape rate undergoes changes as it passes through the midpoint of the phase transition, leading to a reverse escape phenomenon. The findings suggest that the dynamic phase transition in charged AdS black holes affected by entropy change bears a significant resemblance to the outcomes of models influenced by Bekenstein-Hawking entropy\cite{23}. This similarity in results could serve as an additional motivation to further explore the potential capabilities of Kaniadakis and Barrow statistics in related cosmological fields. These capabilities could enhance our understanding of other cosmological properties

gr-qc↗

Bulk-boundary and RPS Thermodynamics from Topology perspective

In this article, we investigate the bulk-boundary and restricted phase space (RPS) thermodynamics of Rissner-Nordström (R-N) AdS and 6-dimensional charged Gauss-Bonnet AdS black holes. Also, we examine the topological characteristics of the considered black holes and compare them with the extended thermodynamics results. In fact, we have found that the topological behavior of the bulk-boundary thermodynamics is the same as that of the extended thermodynamics, whereas the RPS thermodynamics exhibits a distinct behavior. We also demonstrate that within the RPS formalism, there is only one critical point with a topological charge of +1 $(Q_t=+1)$. Additionally, for RPS formalism, the inclusion of higher derivative curvature terms in the form of Gauss-Bonnet gravity does not alter the topological classification of critical points in charged AdS black holes.

gr-qc↗

The Role of Topological Photon Spheres in Constraining the Parameters of Black Holes

In this paper, we investigate the topological photon sphere from two distinct perspectives. In the first view, we examine the existence and characteristics of topological photon(anti-photon)spheres for black holes with different structures, such as Einstein-Young-Mills non-minimal, AdS black holes surrounded by Chaplygin-like dark fluid, and Bardeen-like black holes in Einstein-Gauss-Bonnet gravity. Furthermore, we delve into the deeper perspective of the necessity of photon spheres for super-compact gravitational structures such as black holes. By leveraging this necessity, we propose a classification of the parameter space of black hole models based on the existence and positioning of photon spheres. This approach enables the determination of parameter ranges that delineate whether a solution represents a black hole or a naked singularity. In essence, the paper illustrates the utility of the photon sphere as a notable test for establishing the permissible and non-permissible parameter ranges within specific theories of black hole solutions.

gr-qc↗

Investigation of hidden symmetry in $AdS_{5}$ black hole with Heun equation

Investigating the existence of algebra and finding hidden symmetries in physical systems is one of the most important aspects for understanding their behavior and predicting their future. Expanding this unique method of study to cosmic structures and combining past knowledge with new data can be very interesting and lead to discovering new ways to analyze these systems. However, studying black hole symmetries always presents many complications and sometimes requires computational approximations. For example, checking the existence of Killing vectors and then calculating them is not always an easy task. It becomes much more difficult as the structure and geometry of the system become more complex. In this work, we will show that if the wave equations with a black hole background can be converted in the form of general Heun equation, based on its structure and coefficients, the algebra of the system can be easily studied, and computational and geometrical complications can be omitted. For this purpose, we selected two $AdS_5$ black holes: Reissner-Nordstrom (R-N) and Kerr, and analyzed the Klein-Gordon equation with the background of these black holes. Based on this concept, we observed that the radial part of the R-N black hole and both the radial and angular parts of the Kerr black hole could be transformed into the general form of the Heun equation. As a result, according to the algebraic structure that governs the Heun equation and its coefficients, one can easily achieve generalized $sl(2)$ algebra.

gr-qc↗

Thermodynamic Topology and Photon Spheres in the Hyperscaling violating black holes

It was shown that a standard ring of light can be imagined outside the event horizon for stationary rotating four-dimensional black holes with axial symmetry using the topological method\cite{001,002}. Based on this concept, in this paper, we investigate the topological charge and the conditions of existence of the photon sphere (PS) for a hyperscaling violation (HSV) black hole with various values of the parameters of this model. Then, after carrying out a detailed analysis, we show the conventional topological classes viz $Q=-1$ for the mentioned black hole and $Q=0$ for the naked singularities. \textit{Also, we propose a new topological class for naked singularities (Q=+1) with respect to $z\geq1$. We also determined that $z\geq2$, it either shows a naked singularity form with total topological charge $+1$ or has no solution. Therefore, we have the black hole solution only in $1\leq z<2$}. Then, we will use two different methods, namely the temperature (Duan's topological current $Φ$-mapping theory) and the generalized Helmholtz free energy method, to study the topological classes of our black hole. We discuss the critical and zero points (topological charges and topological numbers) for different parameters of hyperscaling violating black holes, such as ($z, \overlineθ$) and other free parameters, and study their thermodynamic topology. We observe that for a given value of the parameters $1\leq z<2$, $\overlineθ$, and other free parameters, there exist two total topological charges $(Q_{total}=-1, 0)$ with the same phase structure for the $T$ method and total topological numbers $(W=+1)$ for the generalized Helmholtz free energy method. Additionally, we summarize the results for each study as photon sphere, temperature, and generalized Helmholtz free energy in some figures and tables. Finally, we compare our findings with other related studies in the literature.

gr-qc↗

Topological classification and black hole thermodynamics

One of the new methods that can be used to study the thermodynamics critical points of a system based on a topological approach is the study of topological charges using Duan's $ϕ$-mapping method. In this article, we will attempt to use this method to study three different black holes, each with different coefficients in their metric function, in order to determine the class of critical points these black holes have in terms of phase transition. Through this analysis, we found that the Euler-Heisenberg black hole has two different topological classes, and the parameter $"a"$ added to the metric function by QED plays an important role in this classification. While a black hole with a non-linear electrodynamic field, despite having an electromagnetic parameter, which is added to its metric function, has only one topological class, and its $"α"$ parameter has no effect on the number of critical points and topological class. Finally, the Young Mills black hole in massive gravity will have a different number of critical points depending on the coefficient $"c_i"$, which is related to massive gravity and leads to different topological classes. However, this black hole exhibits the same phase structure in all cases.

gr-qc↗