Neutron stars in the generalized SU(2) Proca theory

TL;DR

This paper investigates neutron star solutions within the generalized SU(2) Proca modified gravity theory, revealing increased compactness and masses exceeding 2.5 solar masses, which could impact understanding of compact stellar objects.

Contribution

It models realistic neutron stars in the theory, constrains free parameters, and demonstrates solutions with higher mass and compactness than in general relativity.

Findings

Neutron stars exhibit greater compactness than in GR.

Masses can exceed approximately 2.5 solar masses.

Solutions suggest alternative explanations for the mass gap.

Abstract

The generalized SU(2) Proca theory is a vector-tensor modified gravity theory characterized by an action that remains invariant under both diffeomorphisms and global internal transformations of the SU(2) group. This study aims to further explore the physical properties of the theory within astrophysical contexts. Previous investigations have unveiled intriguing astrophysical solutions, including particle-like configurations and black holes. The purpose of this work is to constrain the theory's free parameters by modeling realistic neutron stars. To that end, we have assumed solutions that are static, spherically symmetric, and have adopted the t'Hooft-Polyakov magnetic monopole configuration for the vector fields. Employing both analytical techniques, such as asymptotic expansions, and numerical methods involving solving boundary value problems, we have obtained neutron star solutions whose baryonic matter is described by realistic equations of state for nuclear matter. Furthermore, we have constructed mass-radius relations which reveal that neutron stars exhibit greater compactness in comparison with general relativity predictions for most of the solutions we have found and for the employed equations of state. Finally, we have found out solutions where the mass of the star is greater than $\sim$ 2.5 $M_\odot$; this result poses an alternative in the exploration of the mass gap of compact stellar objects.