arXiv subjects

Bidyut Hazarika

Publications and source records attributed to Bidyut Hazarika.

At least 19 recordsLinked to original sources

arXiv2026

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

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

gr-qc↗

arXiv2026

Brouwer Degree of Thermodynamic Multicritical Points in Black Holes

In this manuscript, we propose a novel topological framework based on the heat capacity of black holes to investigate the topology of thermodynamic multicritical points. We construct a two-dimensional thermodynamic vector field whose isolated zeros correspond to the critical points of the system. The local topology of each critical point is characterized by its Brouwer degree, which serves as a locally conserved topological quantity. Applying this formalism to several AdS black hole solutions, we demonstrate that each system possesses a globally conserved topological charge. Although the number of thermodynamic critical points changes as the thermodynamic parameters are varied, the total topological charge remains invariant throughout the evolution. We show that these topological transitions are governed by the creation or annihilation of topologically neutral defect pairs carrying opposite Brouwer degrees. Our results provide a unified topological framework for understanding the emergence, evolution, and classification of thermodynamic multicritical points in black hole systems.

hep-th↗

arXiv2026

Degenerate Bifurcations and Universal Relaxation Scaling in Black Hole Thermodynamics

We present a dynamical systems approach to black hole thermodynamic criticality based on bifurcation equations. We construct an effective thermodynamic landscape in which black holes relax toward equilibrium fixed points. To describe this process, we introduce a flow parameter $τ$, interpreted as a phenomenological relaxation time, which governs the approach toward equilibrium configurations in thermodynamic state space. Near critical points, the thermodynamic flow simplifies into universal mathematical forms, which allows different black holes to be grouped into different universality classes based on their critical behaviour. Our analysis further shows critical slowing down, with relaxation timescales determined entirely by the local bifurcation structure.

hep-th↗

arXiv2026

Probing Black Hole Phase Transitions through Quasi-Periodic Oscillations

In this work, we probe the well known thermodynamic phase structure of black hole through the lens of its quasi-periodic oscillations (QPOs). Can QPOs be influenced by black hole phase transitions? Do they carry any signature of such transitions in their observational patterns? These were the central questions guiding our study. Using both RN AdS and Kerr black hole backgrounds across different QPO models, we analyzed the behavior of upper and lower QPO frequencies as functions of the Hawking temperature. Our results shows that QPO frequencies trace out distinct thermodynamic phases and also reflect their stability properties. As the black hole transitions between different thermodynamic phases, the trend of QPO frequencies with respect to temperature also shifts. Due to lack of of observational data, the present work is primarily more on the mathematical side, as the underlying mechanism responsible for the Hawking temperature has not yet been fully understood or experimentally verified. Moreover, given the speculative nature of black hole phase transitions, it would be unfair to claim that our results establish a definitive connection between an observable quantity such as the QPO frequency and the thermodynamic phase behavior of black holes. Nevertheless, our analysis suggests a possibility that changes in black hole geometry could be one of the contributing factors influencing QPO behavior.

gr-qc↗

arXiv2026

Quasi-Periodic Oscillations and Parameter Constraints in ModMax Black Holes

We analyze the impact of ModMax parameter on the dynamics of test particles around black holes and its effect on the characteristics of Quasi-Periodic Oscillations (QPOs). The effect of the ModMax parameter $η$ is studied using the effective potential, angular momentum and the energy of the circular orbits of the test particles. Our analysis shows that increasing $η$ brings about a continuous transition from the RN regime toward the Schwarzschild limit, accompanied by noticeable modifications in the Innermost Stable Circular Orbit (ISCO) and the corresponding Keplerian frequencies. We also explore the dependence of QPO radii on the ModMax parameter $η$ within the framework of the PR, RP, WD, and ER models. Finally, to place observational constraints, we perform a Markov Chain Monte Carlo (MCMC) analysis using QPO data from a range of black hole sources spanning stellar-mass, intermediate-mass, and supermassive scales.

gr-qc↗

arXiv2025

Bifurcation and Critical Phenomena in Black Hole Thermodynamics

In this work, we treat black holes as bifurcation points and explore their thermodynamic phase structure using the framework of bifurcation theory which is a commonly used method from nonlinear dynamics. By constructing an appropriate bifurcating function, we analyze how black holes transition between different thermodynamic phases through changes in the number and stability of fixed points. Our study shows that stable fixed points correspond to thermodynamically stable black hole states, while unstable ones indicate instability and decay. The dynamical evolution of the system further supports this correspondence, with stable configurations approaching equilibrium and unstable ones diverging from it.

gr-qc↗

arXiv2025

Observational Constraints on f(R,T) gravity coupled with NED from Black Hole Quasi Periodic Oscillations

In this work, we examine the influence of nonlinear electrodynamics (NED) and $f(R,T)$ gravity on quasi-periodic oscillations (QPOs) around a magnetically charged black hole. By analyzing the effective potential, specific energy, and angular momentum of circular orbits, we study how the NED parameter $α$ and the gravitational coupling parameter $β$ affect orbital dynamics. Increasing $α$ leads to systematic deviations from the Reissner Nordstrom behavior, reflected in shifts in the ISCO radius and orbital frequencies. We further explore QPO-generating radii using the Relativistic Precession (RP), Warped Disk (WD), and Epicyclic Resonance (ER2-ER4) models. We further extend our analysis by performing an MCMC-based parameter estimation using QPO data from black holes spanning a wide range of mass scales. This approach yields consistent observational constraints on the model parameters.

gr-qc↗

arXiv2025

Probing the Thermodynamic Phase Structure of Black Holes through Euler characteristic

In this work, we attempt to explore a possible connection between thermodynamic topology and the thermodynamic geometry formulation of black hole thermodynamics. We study the topological structure of black hole thermodynamic phase spaces by calculating the Euler characteristic (EC) using four well-known thermodynamic geometries: Weinhold, Ruppeiner, Geometrothermodynamics (GTD), and HPEM. We interpret the Euler characteristic as an indicator of the degree of microscopic interactions within the thermodynamic system. As the system approaches the spinoidal curve, the interaction strength increases significantly, eventually driving a phase transition. Beyond the spinoidal region, the interactions begin to weaken, and the system gradually stabilizes into a new phase configuration, reflected by a corresponding change in the topological structure of the thermodynamic state space.

hep-th↗

arXiv2025

The Interconnection of Cosmological Constant and Renyi Entropy in Kalb-Ramond Black Holes : Insights from Thermodynamic Topology

This paper seeks to establish a connection between the cosmological constant and Renyi entropy within the framework of Kalb-Raymond(K-R) gravity. Our analysis is supported by evidence showing the equivalence of the thermodynamic topology of K-R AdS black holes in the Gibbs-Boltzmann (GB) statistical framework and K-R flat black holes in the Renyi statistical framework. We begin by exploring the thermodynamic topology of K-R black holes in flat spacetimes, focusing on the topological characteristics and phase transition behavior in both statistical frameworks. We find that K-R flat black holes in Renyi statistics exhibit equivalent global and local topological properties to K-R AdS black holes in GB statistics. This equivalence points to a potential connection between the cosmological constant and the Renyi parameter. We derive an approximate relationship between the Renyi parameter and the cosmological constant, which is consistent with similar findings in the literature from a cosmological perspective.

gr-qc↗

arXiv2025

Holographic Einstein Rings of AdS black holes with higher derivative corrections in presence of string cloud

This paper seeks to explore the holographic optical appearance of an AdS black hole with higher derivative corrections in the presence of a string cloud, drawing on the AdS/CFT correspondence and wave optics. We introduce a Gaussian wave source that oscillates at the AdS boundary and propagates through the bulk. The resulting response function is then analyzed using an imaging system to study the optical properties of the black hole. Depending on the observer's position and variations in system parameters, the resulting holographic image takes on different forms, including a well defined Einstein ring, deformed luminous patterns, or isolated bright spots. Notably, when the observer is positioned at the north pole, the image consistently features a bright ring at the photon sphere, encircled by concentric stripes. Our findings reveal a strong correlation between the Einstein ring's location and the photon sphere radius predicted by geometric optics, reinforcing the connection between wave optics and gravitational lensing. Additionally, we examine the influence of higher-derivative corrections and string cloud parameters on the observed optical features.

hep-th↗

arXiv2025

Signatures of NED on Quasi periodic Oscillations of a Magnetically Charged Black Hole

In this work, we explore the influence of nonlinear electrodynamics (NED) on the quasi-periodic oscillations (QPOs) of a magnetic charged black hole by analyzing the motion of test particles and their epicyclic frequencies. Starting from the effective potential, angular momentum, and energy of circular orbits, we examine how the NED parameter b alters the orbital dynamics. We find that as b increases, the system transitions smoothly from the RN regime towards the Schwarzschild profile, with observable changes in the innermost stable circular orbit (ISCO) and Keplerian frequencies. We further investigate the variation in the radii of QPOs with respect to the NED parameter b by employing the RP, WD, and ER models. We also perform Markov Chain Monte Carlo (MCMC) analysis using observational QPO data from a diverse set of black hole sources spanning stellar-mass, intermediate-mass, and supermassive regimes. The MCMC results yield consistent constraints on the parameter b across all mass regimes, indicating that NED effects leave a distinguishable signature on the QPO structure of a charged black hole.

gr-qc↗

arXiv2025

The $D$-dimensional charged AdS black holes solutions in polytropic dark energy from Barrow entropy

This paper mainly aims to solve the Anti deSitter Black Holes (AdS BH) under the Barrow entropy under polytropic gas fluid, especially the Chaplygin Gas. First, we develop this last polytropic model in detail to then obtain the possible solutions and thermodynamic conditions on the Energy-Momentum and the Barrow Entropy for spacetimes of spatial dimension $D>3$. Then, we focus on thermidynamic solutions and the different impacts on the Barrow entropy of the black hole, the temperature profile, the mass and the various physical quantities involved. Afterwards, we focus on the specific cases of the solutions of dimensions $D=4$ and $5$ in order to concretely test the models, especially from the point of view of the thermodynamic topology. Finally, we generalize everything by elaborating and testing the stability of the models to arrive at the thermal geometry of the AdS BH.

gr-qc↗

arXiv2025

RPST-Inspired Formalism for Black Holes in Flat Spacetime

In this work, we propose a novel formalism for the thermodynamics of flat black holes, inspired by the Restricted Phase Space Thermodynamics (RPST) framework. Our construction is motivated by the observed similarities in the thermodynamic behavior of flat black holes within the Rényi entropy framework and that of AdS black holes described by the Bekenstein entropy regime. The RPST framework is, by construction, exclusive to AdS black holes because it depends on the cosmological constant $Λ$, which is linked to the central charge $C$ of the dual conformal field theory (CFT). However, for non-AdS black holes, where $Λ$ is absent, we introduce a deformation parameter $λ$ to replace the central charge $C$. This RPST-inspired formalism incorporates $λ$ and its conjugate variable, the response potential $ζ$, as a new pair of thermodynamic variables, analogous to the central charge $C$ and chemical potential $μ$ in the AdS case. To illustrate the applicability of this formalism, we analyze two examples: the Reissner-Nordström (RN) flat black hole and the Kerr black hole.

hep-th↗

arXiv2025

Thermodynamics of Rotating AdS black holes in Kaniadakis statistics

In this study, we advance the understanding of thermodynamic properties and phase transitions in rotating anti-de Sitter (AdS) black holes by applying the Kaniadakis(KD) entropy framework. This framework represents a non-extensive generalization of classical statistical mechanics, inspired by the symmetries of relativity and offering a novel perspective on black hole thermodynamics. Our focus is on investigating how Kaniadakis entropy modifies the thermodynamic phase space of rotating AdS black holes. To achieve this, we analyze three prominent rotating AdS black hole systems: the Kerr AdS black hole, the Kerr-Sen AdS black hole, and the Kerr-Newman AdS black hole. We assess their thermodynamic quantities, phase transitions, thermodynamic topology and thermodynamic geometry within the Kaniadakis statistical framework. Our analysis reveals notable deviations from the behaviour predicted by traditional Gibbs-Boltzmann(GB) statistics.

gr-qc↗

arXiv2025

Revisiting thermodynamic topology of Hawking-Page and Davies type phase transitions

In this work, we propose a common vector field to study the thermodynamic topology of the Davies type and Hawking-Page phase transitions. Existing literature has shown that studying these two types of phase transitions typically requires defining two separate vector fields . In our approach, we adopt Duan's $ϕ$-mapping topological current theory to define a novel vector field, denoted as $ϕ$, whose critical points exactly correspond to the Davies point and the Hawking-Page phase transition point. More importantly, we can differentiate between these two points by their topological charge. While, the topological charge for the critical point corresponding to the Davies-type phase transition is found to be $-1$, the same for the Hawking-Page phase transition point, it is $+1$. Although our analysis is applicable to all black hole systems where both types of phase transitions are found, we illustrate it using three simple systems as examples: the Schwarzschild AdS black hole, the Reissner-Nordström AdS black hole in the grand canonical ensemble, and finally the Kerr AdS black holes in the grand canonical ensemble. It is wellknown that these black holes exhibit both Davies and Hawking-Page phase transitions. With our proposed vector $ϕ$, the critical points obtained for these three systems exactly match the Davies-type and Hawking-Page phase transition points, and the associated topological charges are found to be $-1$ for the Davies point and $+1$ for the Hawking-Page phase transition point.

hep-th↗

arXiv2025

Topology of restricted phase space thermodynamics in Kerr-Sen-Ads black holes

In this study, we investigate the thermodynamic topology of the Kerr-Sen-Ads black hole in restricted phase space. In the restricted phase space, a new parameter, central charge $C$, and its conjugate parameter $μ$ are introduced, omitting the well-known $PdV$ term in the first law of black hole thermodynamics. We study the local and global topology of the black hole by considering the black hole solution as topological defects in the free energy landscape. We compute the winding number and the total topological number at the thermodynamic defects. For our analysis, we have considered five ensembles of Kerr-Sen-Ads black holes in restricted phase space: fixed $(Q, J, C)$, fixed $(ϕ, J, C)$, fixed $(Q,Ω, C)$, fixed $(Q, J, μ)$, and fixed $(ϕ,Ω, C)$, where $Q$ is the electric charge, $J$ is the angular momentum, $C$ is the central charge, $ϕ$ is the electric potential conjugate to charge, $Ω$ is the angular frequency conjugate to $J$, and finally, $μ$ is the chemical potential. In the fixed $(Q, J, C)$, fixed $(ϕ, J, C)$, and fixed $(Q, J, μ)$ ensembles, we find a topological charge of $+1$. In the fixed $(Q,Ω, C)$ and fixed $(ϕ, Ω, C)$ ensembles, depending on the values of the thermodynamic parameters, we find topological charges of $-1$, $0$, and $+1$. Interestingly, in ensembles where we find the topological charge to be $0$, we observe both Hawking-Page and Davies type phase transitions. We show that both types of these phase transitions can be studied using a common vector field, and the topological charges associated with Davies type and Hawking-Page phase transitions are $-1$ and $+1$, respectively.

hep-th↗

arXiv2025

Thermodynamic Properties and Shadows of Black Holes in $f(R,T)$ Gravity

In this paper, we explore two $f(R,T)$ gravity models and derive black hole solutions within these models. We focus on investigating how the $f(R,T)$ model influences the thermodynamic characteristics of black holes by studying their thermodynamic topology and thermodynamic geometry. We consider five specific values of the thermodynamic parameter $ω$, which signify five different classes of black hole solutions in general relativity (GR). We observe significant changes in the local topological properties of these black holes compared to GR, depending on the model parameters. Notably, we identify an additional topological class $W=0$ for some values of $ω$ that is absent in the GR framework. We also study the thermodynamic geometry of the black hole using the Geometrothermodynamics (GTD) formalism. Our analysis demonstrates that the singular point, where the GTD scalar curvature diverges, corresponds exactly to the point where the heat capacity changes sign. Additionally, we constrain the model parameters of both models considered by utilizing black hole shadow data from the Sgr A* black hole, measured by the Event Horizon Telescope (EHT).

gr-qc↗

arXiv2024

Thermodynamic topology of topological charged dilatonic black holes

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

hep-th↗