Fermion soliton stars

TL;DR

This paper introduces fermion soliton stars as stable, self-gravitating solutions involving a scalar field and fermions within General Relativity, with potential astrophysical implications.

Contribution

First comprehensive study of fermion soliton stars in full General Relativity, including their properties and potential astrophysical relevance.

Findings

Existence of static, spherically symmetric solutions

Mass-radius relationship and maximum compactness analyzed

Potential for astrophysical objects like neutron star analogs

Abstract

A real scalar field coupled to a fermion via a Yukawa term can evade no-go theorems preventing solitonic solutions. For the first time, we study this model within General Relativity without approximations, finding static and spherically symmetric solutions that describe fermion soliton stars. The Yukawa coupling provides an effective mass for the fermion, which is key to the existence of self-gravitating relativistic solutions. We systematically study this novel family of solutions and present their mass-radius diagram and maximum compactness, which is close to (but smaller than) that of the corresponding Schwarzschild photon sphere. Finally, we discuss the ranges of the parameters of the fundamental theory in which the latter might have interesting astrophysical implications, including compact (sub)solar and supermassive fermion soliton stars for a standard gas of degenerate neutrons and electrons, respectively.