arXiv subjects

F. Barzi

Publications and source records attributed to F. Barzi.

8 recordsLinked to original sources

arXiv2026

On Accretion and Neutrino Investigations of Thermodynamically Reconstructed Black Holes from Three-Parameter Generalized Entropy

We study accretion and neutrino-sensitive thermal signatures of a static black hole reconstructed from a three-parameter generalized entropy. The construction is thermodynamic by design: the entropy deformation is not mapped to a radial-coordinate redefinition or to a prescribed Reissner--Nordstr\"om-like correction. Instead, the generalized entropy fixes the horizon response factor $\Xi_h=dS_G/dS|_{S_h}$. The effective exterior geometry is then reconstructed by requiring its surface-gravity temperature to reproduce the generalized thermodynamic temperature. As a result, the metric preserves the horizon area and the Schwarzschild asymptotics, and reduces smoothly to Schwarzschild when $\Xi_h\to1$. The deformation is controlled by $\lambda_G=1/\Xi_h-1$, while the integer $p\geq2$ determines the radial localization of the near-horizon correction. We compute the photon sphere, critical shadow scale, circular geodesics, ISCO, Novikov--Thorne flux, disk temperature, radiative efficiency, energy-at-infinity luminosity, a redshifted spectral proxy, and neutrino-sensitive temperature moments. In particular, positive $\lambda_G$ moves the photon sphere and ISCO inward, decreases the shadow scale, raises the radiative efficiency, and concentrates the energy release toward the inner disk. By contrast, negative $\lambda_G$ produces the opposite trend. Finally, the neutrino sector is modeled conservatively using dimensionless temperature moments instead of a full neutrino-dominated accretion flow or annihilation-deposition calculation. The hierarchy among the $ n=4$, $n=6$, and $n=9$ moments reveals that entropy-induced disk deformation becomes increasingly apparent with higher temperature exponents. Thus, observable changes in compact orbits and thin-disk emission can be directly linked to generalized entropy via the horizon response.

gr-qc↗

arXiv2025

Modified Unruh Thermodynamics in Emergent Gravity: Finite Heat Capacity and R\'enyi Entropy

We show that Jacobson's thermodynamic derivation of Einstein's equations remains valid when local Rindler horizons are treated as finite heat-capacity systems, resolving the unphysical infinite-bath assumption of standard Unruh thermodynamics. The resulting entropy takes the form of R\'enyi entropy with nonextensivity parameter $\lambda\sim C^{-1}$, or equivalently, a new "Einstein entropy" that exactly preserves the Einstein equations for all heat capacities. In both cases, the Unruh temperature is modified as \begin{equation*} T_\text{mod}=\frac{\hbar\kappa}{2\pi}\left(1+\frac{S}{C}\right), \end{equation*} establishing a universal link between finite-capacity thermodynamics and nonextensive entropy. We further obtain a corrected scalar Einstein equation with an upper bound on horizon energy flux, pointing to testable signatures in heavy-ion collisions, accelerator spin polarization, and analog gravity experiments. These results reinforce the robustness of the emergent-gravity paradigm and connect spacetime dynamics to generalized entropies of quantum information theory.

hep-th↗

arXiv2025

On R\'enyi Microstructural Aspects of Asymptotically Flat Charged Black Holes: A Novel Duality

We explore the microstructure of asymptotically flat charged black holes through the lens of nonextensive R\'enyi statistics. A modified form of the R\'enyi entropy is proposed to incorporate compressibility effects, and geometrothermodynamics is applied within such a framework. Besides, by quantizing the black hole horizon area, we derive a microscopic description in terms of discrete degrees of freedom, with R\'enyi entropy providing a nonextensive generalization of the Bekenstein-Hawking entropy. We compute the R\'enyi partition function and probability distribution in the canonical ensemble, highlighting significant deviations from Boltzmann-Gibbs behavior at finite temperature due to nonextensive effects. The black hole undergoes a first-order Van der Waals-like phase transition between small and large configurations, characterized by discontinuities in entropy and latent heat, both of which are shown to depend on the number of area quanta. A critical threshold emerges beyond which the transition becomes athermal. Additionally, we establish a thermodynamic duality between charged-AdS black holes in Boltzmann-Gibbs statistics and charged-flat R\'enyi black holes, expressed via a conformal transformation of state variables. This duality extends naturally to higher dimensions. Our results provide new insights into the microstructure of black holes.

hep-th↗

arXiv2024

Nonextensive Black Hole Thermodynamics from Generalized Euclidean Path Integral and Wick's Rotation

This paper extends the Euclidean path integral formalism to account for nonextensive statistical mechanics. Concretely, we introduce a generalized Wick's rotation from real time $t$ to imaginary time $\tau$ such that, $t\rightarrow-i f_\alpha(\tau)$, where $f_\alpha$ a differentiable function and $\alpha$ is a parameter related to nonextensivity. The standard extensive formalism is recovered in the limit $\alpha\rightarrow0$ and $f_0(\tau)=\tau$. Furthermore, we apply this generalized Euclidean path integral to black hole thermodynamics and derive the generalized Wick's rotations given the nonextensive statistics. The proposed formulation enables the treatment of nonextensive statistics on the same footing as extensive Gibbs-Boltzmann statistics. Moreover, we define a universal measure, $\eta$, for the nonextensivity character of statistics. Lastly, based on the present formalism, we strengthen the equivalence between the AdS-Schwarzschild black hole in Gibbs-Boltzmann statistics and the flat-Schwarzschild black hole within R\'enyi statistics and suggest a potential reformulation of the $AdS_5$/$CFT_4$ duality.

hep-th↗

arXiv2024

Riemann Surfaces and Winding Numbers of R\'enyi Phase Structure of Charged-Flat Black Holes

It's widely recognized that the free energy landscape captures the essentials of thermodynamic phase transitions. In this work, we extend the findings of [1] by incorporating the nonextensive nature of black hole entropy. Specifically, the connection between black hole phase transitions and the winding number of Riemann surfaces derived through complex analysis is extended to the R\'enyi entropy framework. This new geometrical and non-extensive formalism is employed to predict the phase portraits of charged-flat black holes within both the canonical and grand canonical ensembles. Furthermore, we elucidate novel relations between the number of sheets comprising the Riemann surface of the Hawking-Page and Van der Waals transitions and the dimensionality of black hole spacetimes. Notably, these new numbers are consistent with those found for charged-AdS black holes in Gibbs-Boltzmann statistics, providing another significant example of the potential connection between the cosmological constant and the nonextensive R\'enyi parameter.

hep-th↗

arXiv2024

Thermal chaos of charged-flat black hole via R\'enyi formalism

Charged-flat black holes in the R\'enyi extended phase space demonstrate phase structures akin to those of a van der Waals fluid in four-dimensional spacetime and mirror the behaviors of Reissner-Nordstrom-Anti-de-Sitter black holes within the standard Gibbs-Boltzmann extended phase space. This study delves into the dynamics of states initially positioned within the unstable spinodal region of the phase space associated with the charged-flat black hole when subjected to time-periodic thermal perturbations. Our analysis based on the Mel'nikov method reveals that chaos emerges when the $\delta$ parameter surpasses a critical threshold, $\delta_c$. This critical quantity is dependent on the black hole charge; notably, a larger value of $Q$ impedes the onset of chaos. Furthermore, we examine the effects of space-periodic thermal perturbations on its equilibrium state and find that chaos invariably occurs, irrespective of the perturbation amplitude. Hence, the chaotic dynamics observed in the analysis of charged-flat black holes under R\'enyi statistics exhibit resemblances to those of asymptotically AdS-charged black holes investigated via the Gibbs-Boltzmann formalism. This serves as yet another example of a potential and significant connection between the cosmological constant and the nonextensivity R\'enyi parameter.

hep-th↗

arXiv2023

R\'enyi Topology of Charged-flat Black Hole: Hawking-Page and Van-der-Waals Phase Transitions

In this paper, we extend the proposed setup in [1,2] for finding the topological charges associated with the Hawking-Page and Van-der-Waals transition points as well as equilibrium phases to catch the nonextensive nature of the black hole entropy, Rigorously speaking we incorporate the R\'enyi statistics formalism in off-shell Bragg-Williams free energy landscape to examine topologically the Hawking-Page phase transition related to the uncharged/charged-flat black hole in grand canonical and the Van-der- Waals transition in the canonical ensemble and where a vortex/anti-vortex structure is found. For this purpose, we introduce three mappings, the $\psi$- and $\xi$-mapping, for phase transitions classification and the $\eta$-mapping for equilibrium phases classification. We found that Hawking-Page and Van-der-Waals phase transitions belong to different topological classes and exhibit an interplay of total charge values hinting to a possible new correspondence. Our topological study provides further substantiation for a possible conjecture positing a correspondence between the thermodynamic characteristics of black holes in asymptotically flat spacetime using R\'enyi statistics, and those in asymptotically Anti-de-Sitter spacetime employing Gibbs-Boltzmann statistics.

hep-th↗

arXiv2023

On some phase equilibrium features of charged black holes in flat spacetime via R\'enyi statistics

Motivated by the nonextensive nature of entropy in gravitational context and the Gauge/Gravity duality, black hole thermodynamics has been attracting intense emphasis in the literature. Along the present work, we investigate some features of the phase structure and critical phenomena of the 4-dimensional charged black holes in asymptotically flat spacetime within the formalism of R\'enyi statistics. First, we explore the extended phase space via the R\'enyi statistics approach. Concretely, based on the modified version of the Smarr formula, we recall the equal-area law to remove the oscillatory non-physical region in the $P_R-V$ and $T_R-S_R$ planes. Then, the coexistence curves are determined, as well as the latent heat of phase change. Moreover, we prove that the critical exponent describing the behavior of the order parameter near the critical point is $\frac{1}{2}$, which is consistent with Landau's theory of continuous phase transition. Lastly, we apply the Hamiltonian approach to R\'enyi thermodynamics which provides a new and solid mathematical basis for the extension of phase space and puts more insight into an expected and profound possible connection between the nonextensivity R\'enyi parameter $\lambda$ and the cosmological constant $ \Lambda$.

gr-qc↗