Phase transition of charged Black Holes in Brans-Dicke theory through geometrical thermodynamics

TL;DR

This paper studies the thermodynamics and phase transitions of charged black holes in Brans-Dicke theory, using geometrical thermodynamics and heat capacity analysis to identify second order phase transitions and physical bounds.

Contribution

It introduces a geometrical thermodynamics approach to analyze phase transitions in charged Brans-Dicke black holes, revealing new insights into their stability and physical bounds.

Findings

Black holes exhibit second order phase transitions.

A lower bound on horizon radius due to temperature positivity.

Thermodynamical Ricci scalar divergences identify phase transitions.

Abstract

In this paper, we take into account black hole solutions of Brans-Dicke-Maxwell theory and investigate their stability and phase transition points. We apply the concept of geometry in thermodynamics to obtain phase transition points and compare its results with those, calculated in canonical ensemble through heat capacity. We show that these black holes enjoy second order phase transitions. We also show that there is a lower bound for the horizon radius of physical charged black holes in Brans-Dicke theory which is originated from restrictions of positivity of temperature. In addition, we find that employing specific thermodynamical metric in the context of geometrical thermodynamics, yields divergencies for thermodynamical Ricci scalar in places of the phase transitions. It will be pointed out that due to characteristics behavior of thermodynamical Ricci scalar around its divergence points, one is able to distinguish the physical limitation point from the phase transitions. In addition, the free energy of these black holes will be obtained and its behavior will be investigated. It will be shown that the behavior of the free energy in the place where the heat capacity diverges, demonstrates second order phase transition characteristics.