Relativistic stars in bigravity theory

TL;DR

This paper investigates relativistic star solutions in ghost-free bigravity theory, revealing differences in maximum neutron star mass depending on coupling classes and the effectiveness of the Vainshtein screening mechanism.

Contribution

It provides the first detailed analysis of relativistic stars in bigravity, classifying coupling constants and examining the Vainshtein mechanism's role in different classes.

Findings

Class I stars have a smaller maximum mass than in GR due to no regular solutions beyond a critical compactness.

Class II stars exhibit effective Vainshtein screening, recovering GR results.

The study highlights how bigravity coupling classes influence neutron star properties.

Abstract

Assuming static and spherically symmetric spacetimes in the ghost-free bigravity theory, we find a relativistic star solution, which is very close to that in general relativity. The coupling constants are classified into two classes: Class [I] and Class [II]. Although the Vainshtein screening mechanism is found in the weak gravitational field for both classes, we find that there is no regular solution beyond the critical value of the compactness in Class [I]. This implies that the maximum mass of a neutron star in Class [I] becomes much smaller than that in GR. On the other hand, for the solution in Class [II], the Vainshtein screening mechanism works well even in a relativistic star and the result in GR is recovered.