The thermodynamic profile of AdS black holes in Lorentz-violating Bumblebee and Kalb-Ramond gravity

TL;DR

This paper investigates how Lorentz invariance violation influences the thermodynamics of AdS black holes in Bumblebee and Kalb-Ramond gravity, revealing modified phase transitions and microstructure signatures.

Contribution

It provides a comparative analysis of LIV effects on black hole thermodynamics in Bumblebee and Kalb-Ramond models, highlighting distinctive signatures and phase transition modifications.

Findings

LIV alters Hawking-Page phase transition stability regimes.

Larger black holes show negligible LIV effects, behaving like an ideal gas.

Shorter scale black holes exhibit multiple phase transitions due to LIV.

Abstract

Lorentz invariance violation (LIV) is a topic of significant interest in quantum gravity and in extensions of the Standard Model of particle physics. Recently, new classes of black hole solutions have been proposed, involving vector fields and rank-two antisymmetric tensor fields that acquire nontrivial vacuum expectation values, resulting in the Bumblebee and Kalb-Ramond (KR) gravity models, respectively. These models exhibit novel geometric structures and differ in notable ways from standard Einstein gravity. In this study, we examine neutral anti-de Sitter (AdS) black holes within the context of LIV backgrounds, focusing on their thermodynamic properties through two distinct approaches. The first approach utilizes the free energy landscape framework, revealing substantial modifications to the conventional Hawking-Page phase transition. Specifically, LIV effects can alter the stability regimes of black holes and thermal AdS phases, potentially leading to overlapping thermodynamic regimes that would otherwise remain distinct. The second approach involves thermodynamic Ruppeiner geometry, which provides a window into the microstructure of black holes via a well-defined scalar curvature. In general, LIV effects are negligible for larger black holes, which behave like an ideal gas with no significant interactions among their constituents. However, at shorter length scales, the presence of LIV can induce multiple stable and unstable phase transitions, depending on the specific gravity model and the magnitude of LIV effects considered. While Bumblebee and Kalb-Ramond gravity share several similarities, we identify distinctive signatures arising from their underlying physical mechanisms. These differences may provide key observational and theoretical constraints for testing LIV effects in black hole physics.