Rapidly rotating neutron stars with a massive scalar field - structure and universal relations

TL;DR

This paper models rapidly rotating neutron stars within massive scalar-tensor theories, revealing significant deviations from general relativity and demonstrating the potential of universal relations to test alternative gravity theories.

Contribution

It extends neutron star modeling to include rapid rotation in massive scalar-tensor theories and analyzes the universality of I-Q relations under these conditions.

Findings

Deviations from GR can be large within observational bounds.

Universal I-Q relations remain approximately EOS independent.

Rapid rotation amplifies differences from GR.

Abstract

We construct rapidly rotating neutron star models in scalar-tensor theories with a massive scalar field. The fact that the scalar field has nonzero mass leads to very interesting results since the allowed range of values of the coupling parameters is significantly broadened. These deviations from pure general relativity can be very large for values of the parameters that are in agreement with the observations. The rapid rotation can magnify the differences several times compared to the static case. The universal relations between the normalized moment of inertia and quadrupole moment are also investigated both for the slowly and rapidly rotating cases. The results show that these relations are still EOS independent up to a large extend and the deviations from pure general relativity can be large. This places the massive scalar-tensor theories amongst the few alternative theories of gravity that can be tested via the universal $I$-Love-$Q$ relations.