arXiv subjects

Abhishek Baruah

Publications and source records attributed to Abhishek Baruah.

9 recordsLinked to original sources

arXiv2026

Testing the AdS/CFT Correspondence Through Thermodynamic Geometry of Nonlinear Electrodynamics AdS Black Holes with Generalized Entropies

We investigate the thermodynamics and thermodynamic geometry of several Anti--de Sitter black hole solutions arising from nonlinear electromagnetic theories, namely the ModMax, nonlinear electrodynamics (NED), and Euler--Heisenberg AdS black holes, together with their holographically dual conformal field theory (CFT) descriptions. The analysis is carried out within three entropy frameworks: the standard Bekenstein--Hawking entropy and the generalized Rényi and Kaniadakis entropies. For each system, we analyze the phase structure through the behavior of temperature, specific heat, and the scalar curvature obtained from geometrothermodynamics (GTD). We find that thermodynamic critical points correspond to extrema in the temperature--entropy relation and coincide with divergences of the specific heat. These locations are reproduced by singularities in the Legendre--invariant GTD curvature, demonstrating a consistent geometric interpretation of the phase transitions. A comparison between the bulk black hole systems and their dual CFT counterparts shows that the number and structure of critical points are preserved under the holographic correspondence. Our results further reveal that the Euler--Heisenberg AdS black hole exhibits a more intricate phase structure compared with the ModMax and NED cases, while the Kaniadakis entropy consistently generates an additional critical point across all systems considered. These findings highlight the combined influence of nonlinear electromagnetic dynamics and generalized entropy formalisms on the critical behavior of AdS black holes and their dual CFTs.

hep-th↗

arXiv2026

Ensemble Dependent Holographic Phase Transitions in 4$D$ Dyonic AdS Black Holes

This work studies the holographic thermodynamics of $4D$ dyonic Anti--de Sitter black holes within the AdS/CFT correspondence. By allowing variations of the cosmological constant $Λ$ and Newton's constant $G_N$, the gravitational thermodynamics is extended to include the CFT central charge $C$ and its conjugate chemical potential $μ$, together with the standard thermodynamic pair $(T,S)$. A further conjugate pair $(p,\mathcal{V})$, interpreted as the CFT pressure and volume, is also introduced. The presence of both electric and magnetic charges, described by $(\tildeΦ_e,\tilde{Q}_e)$ and $(\tildeΦ_m,\tilde{Q}_m)$, leads to a significantly enriched phase structure. A systematic analysis of all sixteen thermodynamic ensembles reveals a strong dependence of phase behavior on ensemble choice. In the ensembles $(\tilde{Q}_m,\tildeΦ_e,\mathcal{V},C)$ and $(\tilde{Q}_e,\tildeΦ_m,\mathcal{V},C)$, the system exhibits Van der Waals transitions, superfluid $λ$ transitions, and Davies criticality, while the ensemble $(\tilde{Q}_m,\tilde{Q}_e,\mathcal{V},C)$ supports similar transitions except for the Davies transitions. When the chemical potential $μ$ is fixed, only Davies--type transitions occur. Ensembles involving the CFT pressure $p$ show no critical behavior, although Davies transitions persist. Notably, the ensemble $(\tildeΦ_m,\tildeΦ_e,\mathcal{V},C)$ uniquely displays a confined/deconfined transition alongside Davies criticality. These results highlight the crucial role of dyonic charges and CFT variables in shaping holographic phase transitions.

hep-th↗

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

Holographic Fractional Order Phase Transitions in CFTs Dual to AdS Black Holes

In this work, we investigate the CFT phase transitions of various AdS black hole solutions, including the Reissner-Nordström-AdS (RN-AdS) black hole, the ModMax-AdS black hole, and the RN-AdS black hole formulated within the framework of Kaniadakis statistics, through the lens of the AdS/CFT correspondence. Employing the generalized Ehrenfest classification scheme based on fractional-order derivatives, we analyze the nature of phase transitions at both Davies points and critical points. Davies points, defined as the loci of divergent heat capacity, are typically associated with second-order transitions in the classical Ehrenfest paradigm. However, a refined analysis reveals that these points can be categorized into two distinct types: the first corresponds to extrema in the temperature profile, while the second aligns with its inflection point, i.e., the thermodynamic critical point. Our findings demonstrate that the order of the phase transition is sensitive to this classification, with the first type corresponding to a fractional order of $3/2$, and the second to $4/3$, which is consistent across RN-AdS black holes. Notably, when a specific constraint is imposed, we observe a $3/2$-order phase transition for both the RN-AdS and ModMax-AdS black holes, whereas in the case of the RN-AdS black hole with Kaniadakis statistics, two critical points arise under constrained paths, each exhibiting a transition of order $4/3$. This generalized, fractional-order framework enables a more precise and discriminating characterization of CFT phase transitions in holographic settings, revealing distinctions that remain hidden under traditional classifications. The results provide deeper insight into the rich structure of black hole thermodynamics on the CFT side and highlight the significance of fractional calculus as a powerful tool for probing critical phenomena within the AdS/CFT framework.

hep-th↗

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

Holographic Einstein Ring of AdS Reissner Nordstr$\ddot{o}$m Black Holes with Euler Heisenberg Nonlinear Electrodynamics

This study, situated within the framework of the AdS/CFT correspondence, employs wave optics methods to investigate the Einstein ring structure of quantum corrected AdS Reissner Nordstr$\ddot{o}$m black holes governed by Euler Heisenberg nonlinear electrodynamics. A wave source placed on the AdS boundary yields a response function on the antipodal side, from which a virtual optical system with a convex lens reconstructs the holographic image of the Einstein ring. The analysis systematically explores the impact of physical parameters and observer position on the ring's morphology. As the observer's position varies, the image transitions from a complete ring to an arc and eventually to a single bright point. The Einstein ring radius is observed to decrease with increasing radial source position $ρ$, wave frequency $ω$, and chemical potential $μ$, while it increases with electric charge $e$ and temperature $T$. In contrast, the quantum correction parameter $a$ has negligible effect on the ring radius or response amplitude, as its contribution falls off rapidly near the boundary and remains subleading in the wave dynamics. The parameter $e$ enhances the electromagnetic lensing strength, leading to a broader ring, whereas increasing $ρ$ alters wavefront propagation, affecting both brightness peak and ring location. Geometric optics analysis confirms that the incident angle of the photon ring matches the Einstein ring angle, validating consistency across frameworks. Overall, the results highlight how nonlinear electromagnetic effects and bulk field configurations manifest in observable boundary features, providing a means to distinguish quantum-corrected black holes from classical solutions.

hep-th↗

arXiv2025

CFT Phase Transition Analysis of Charged, Rotating Black Holes in $D=4$: A Holographic Thermodynamics Approach

We investigate the holographic thermodynamics of 4-D Kerr-Newman AdS black holes, focusing on the conformal thermal states that are dual to these black holes. We explore the thermodynamic behavior within specific ensembles characterized by fixed sets of variables: $(\mathcal{Q},\mathcal{J},\mathcal{V},C)$, $(\mathcal{Q},Ω,\mathcal{V},C)$, $(φ,Ω,\mathcal{V},C)$, $(φ,\mathcal{J},\mathcal{V},C)$, $(\mathcal{Q},Ω,p,C)$, and $(φ,Ω,p,C)$. Here, $φ$, $\mathcal{Q}$, $Ω$, $\mathcal{J}$, $p$, $\mathcal{V}$, and $C$ represent the electric potential, electric charge, angular velocity, angular momentum, CFT pressure, CFT volume, and central charge, respectively. The inclusion of both charge and momentum significantly enriches the regime of phase transitions, leading to a variety of phenomena including first-order Van der Waals-type phase transitions, (de)confinement phase transitions, Davies-type phase transitions, and second-order superfluid $λ$-type phase transitions. Notably, the introduction of the CFT pressure variable allows us to identify phase transitions and critical behavior in the $(\mathcal{Q},Ω,p,C)$ and $(φ,Ω,p,C)$ ensembles, which had not been previously observed. This study underscores the complexity and richness of phase transitions in these systems due to the inclusion of both charge and angular momentum.

hep-th↗

arXiv2024

Restricted Phase Space Thermodynamics of 4D Dyonic AdS Black Holes: Insights from Kaniadakis Statistics and Emergence of Superfluid $λ$-Phase Transition

We study the thermodynamics of $4D$ dyonic AdS black hole in the Kaniadakis statistics framework using the Restricted Phase Space (RPST) formalism. This framework provides a non-extensive extension of classical statistical mechanics, drawing inspiration from relativistic symmetries and presenting a fresh perspective on black hole thermodynamics. Our study analyzes how including Kaniadakis entropy modifies the phase transition of the dyonic black holes. We consider the central charge $C$ and its conjugate chemical potential $μ$ as the thermodynamic variable along with others except the pressure and volume. Due to the addition of the magnetic charge $\tilde{Q}_m$, the study of the phase transition becomes much richer by obtaining a non-equilibrium phase transition from an unstable small black hole to a stable large black hole along with the Van der Waals phase transition in the $T-S$ processes. In the $F-T$ plot, we get an extra Hawking-Page phase transition. Including the deformation parameter $κ$ introduces an unstable (ultra-large BH) branch seen in almost all the plots. Turning off the magnetic charge flips the direction of the phase transition seen during its presence. We observe a novel phenomenon that is the superfluid $λ$ phase transition in the mixed $(\tildeΦ_e,\tilde{Q}_m)$ which is due to the additional $\tilde{Q}_m$ inclusion. Also, in the plots varying $κ$ match with the plot varying $C$ which underlines some sort of correspondence in its meaning which is not possible to observe in Gibbs-Boltzmann statistics. As the entropy models change the homogeneity is not lost where mass is of the first order and the rest is zeroth order. Finally, the $μ-C$ processes in quite similar across black hole systems and entropy formulation marking some kind of universality of this process.

hep-th↗

arXiv2024

Restricted Phase Space Thermodynamics of Dyonic AdS Black Holes: Comparative Analysis Using Different Entropy Models

We study the Restricted Phase Space Thermodynamics (RPST) for the AdS dyonic black hole carrying the central charge $C$ and the chemical potential $μ$, neglecting the pressure and conjugate volume along with comparison of different entropy models namely the Bekenstein-Hawking and the Rényi entropy model. Inclusion of the magnetic charge $\tilde{Q}_m$ gives rise to a richer phase structure of the study of thermodynamics by adding a non-equilibrium transition from an unstable small black hole to a stable black hole on top of the Van der Waals transition in the $T-S$ processes and a Hawking-Page transition in the $F-T$ plots. We study an extra mixed ensemble ($\tildeΦ_e,\tilde{Q}_m)$ due to the inclusion of $\tilde{Q}_m$ where we see Van der Waals phase transition and whose plots change as the entropy model changes though the style of transition remains the same. We observe an interesting phenomenon where changing the Rényi parameter $λ$, the $T-S$ process changes the same way as when varying the central charge $C$ underlining some similarity that is not seen in the Bekenstein Hawking entropy model. We observe a similarity between the plots when both charges are turned off relating to the Schwarzschild black hole and the grand-canonical ensemble. One can observe that as the entropy models are changed, the homogeneity is not lost where the mass as a function of extensive variables is of order one and the rest zero. Finally, we see a similarity in the $μ-C$ process across the entropy models signally some universality across entropy models as well as different types of black holes studied before.

hep-th↗