Thermodynamics of Hairy Black Holes in Quantum Regimes: Insights from Horndeski Theory

Abstract

We study non-perturbative quantum gravitational corrections to the thermodynamics and quantum work distribution of the $n$-dimensional Schwarzschild--Tangherlini--Anti-de Sitter black hole. Starting from the corrected entropy $S = S_0 + η\, e^{-S_0}$, where $S_0$ is the Bekenstein--Hawking entropy, we derive the modified specific heat, internal energy, Helmholtz free energy, and Gibbs free energy in closed form. The specific heat retains the classical divergence at $r_h^{*}=l\sqrt{(n-3)/(n-1)}$ for $n\geq 4$, but the quantum correction suppresses its magnitude by up to $78\%$ at small horizon radii. In the extended phase space, the uncharged black hole admits no van der Waals critical point; however, the non-perturbative correction induces a Hawking--Page transition for $n\geq 4$ that is absent in the semi-classical limit. The corrected Gibbs free energy turns negative at small $r_h$, opening a thermodynamic channel with no classical counterpart. Using the Jarzynski equality and Jensen inequality, we obtain the quantum work distribution during evaporation. The free energy difference $ΔF$ between two black hole states undergoes a sign reversal at small horizon radii for $n\geq 4$ when $η=1$, flipping the average quantum work from negative to positive. This sign reversal grows with the spacetime dimension, reaching $\langle W\rangle \approx +4.31$ for $n=10$. These findings demonstrate that non-perturbative quantum gravitational effects qualitatively alter the phase structure and evaporation energetics of AdS black holes, and they cannot be captured by perturbative corrections alone.

Figures (7)

• Figure 1: Metric function $f(r)$ for the $n$-dimensional ST--AdS BH with $M=1$ and $l=1$.
• Figure 2: Hawking temperature of the $n$-dimensional ST--AdS BH as a function of $r_{h}$, for $l=1$.
• Figure 3: Corrected entropy $S$ as a function of $r_{h}$ for the $n=4$ ST--AdS BH with $l=1$. The dotted blue curve is the uncorrected Bekenstein--Hawking entropy ($\eta=0$), and the solid red curve includes the non-perturbative correction ($\eta=1$). The deviation is pronounced only at small horizon radii.
• Figure 4: Specific heat $C_{V}$ of the $n$-dimensional ST--AdS BH for $l=1$. Panels correspond to $n=3$ (top left), $n=4$ (top right), $n=5$ (bottom left), and $n=10$ (bottom right). Solid curves: $\eta=0$; dashed curves: $\eta=1$. The divergence at $r_{h}^{*}=l\sqrt{(n-3)/(n-1)}$ marks the phase transition for $n\geq 4$.
• Figure 5: Internal energy $E$ of the $n$-dimensional ST--AdS BH for $l=1$. Panels correspond to $n=3$ (top left), $n=4$ (top right), $n=5$ (bottom left), and $n=10$ (bottom right). Solid curves: $\eta=0$; dashed curves: $\eta=1$.