Spinning gauged boson and Dirac stars: a comparative study

TL;DR

This paper compares gauged scalar boson stars and Dirac stars, analyzing how minimal electromagnetic coupling affects their properties, especially focusing on differences in their gyromagnetic ratios.

Contribution

It introduces gauge coupling into scalar and Dirac star models and compares their properties, highlighting differences in gyromagnetic ratios and configurations.

Findings

Scalar stars have gyromagnetic ratio around 1.

Dirac stars have gyromagnetic ratio around 2.

Spinning solutions can be toroidal for both types.

Abstract

Scalar boson stars and Dirac stars are solitonic solutions of the Einstein{Klein-Gordon and Einstein- Dirac classical equations, respectively. Despite the different bosonic vs: fermionic nature of the matter field, these solutions to the classical field equations have been shown to have qualitatively similar features [1]. In particular, for spinning stars the most fundamental configurations can be in both cases toroidal, unlike spinning Proca stars that are spheroidal [2]. In this paper we gauge the scalar and Dirac fields, by minimally coupling them to standard electromagnetism. We explore the impact of the gauge coupling on the resulting solutions. One of the most relevant difference concerns the gyromagnetic ratio, which for the scalar stars takes values around 1, whereas for Dirac stars takes values around 2.