Scalarized Einstein-Maxwell-scalar Black Holes in a Cavity

TL;DR

This paper investigates how Reissner-Nordström black holes in a cavity can spontaneously develop scalar hair due to a tachyonic instability in an Einstein-Maxwell-scalar model, revealing new phase transition phenomena.

Contribution

It numerically constructs scalarized black hole solutions in a cavity within an EMS model and analyzes their stability and phase structure, highlighting novel reentrant phase transitions.

Findings

Scalarized solutions are thermodynamically favored over scalar-free ones.

A reentrant phase transition occurs for large electric charge Q.

Scalarization is driven by a tachyonic instability of the scalar field.

Abstract

In this paper, we study the spontaneous scalarization of Reissner-Nordstr{\"o}% m (RN) black holes enclosed by a cavity in an Einstein-Maxwell-scalar (EMS) model with non-minimal couplings between the scalar and Maxwell fields. In this model, scalar-free RN black holes in a cavity may induce scalarized black holes due to the presence of a tachyonic instability of the scalar field near the event horizon. We calculate numerically the black hole solutions, and investigate the domain of existence, perturbative stability against spherical perturbations and phase structure. The scalarized solutions in a cavity are always thermodynamically preferred over scalar-free solutions. In addition, a reentrant phase transition, composed of a zeroth-order phase transition and a second-order one, occurs for large enough electric charge $Q$.