Scalarization of horizonless reflecting stars: neutral scalar fields non-minimally coupled to Maxwell fields

TL;DR

This paper investigates how non-minimal coupling between scalar and Maxwell fields can lead to scalar hair formation around horizonless reflecting stars, extending previous no-hair results for minimal coupling.

Contribution

It introduces non-minimal coupling in the Einstein-Maxwell-scalar model and demonstrates the existence of scalar hair for large coupling parameters, providing new insights into scalar field configurations.

Findings

No scalar hair for small coupling parameters.

Scalar hair solutions exist for large coupling parameters.

Analytical and numerical methods confirm scalar hair formation.

Abstract

We analyze condensation behaviors of neutral scalar fields outside horizonless reflecting stars in the Einstein-Maxwell-scalar gravity. It was known that minimally coupled neutral scalar fields cannot exist outside horizonless reflecting stars. In this work, we consider non-minimal couplings between scalar fields and Maxwell fields, which is included to aim to trigger formations of scalar hairs. We analytically demonstrate that there is no hair theorem for small coupling parameters below a bound. For large coupling parameters above the bound, we numerically obtain regular scalar hairy configurations supported by horizonless reflecting stars.