Radial Oscillations of Neutron Stars with Vector-Induced Scalar Hair

TL;DR

This study explores how vector-induced scalar hair in gauge-invariant Scalar-Vector-Tensor theories influences neutron star structure, oscillations, and stability, revealing significant modifications to their mass-radius relation and oscillation spectrum.

Contribution

It provides the first detailed analysis of radial oscillations and stability of neutron stars in SVT theories with vector-induced scalar hair, including quasinormal modes.

Findings

Modified gravity affects neutron star mass-radius relation.

Radial oscillation spectrum is significantly altered.

Radial stability criterion remains consistent with GR.

Abstract

In this paper, we investigate the equilibrium configurations and radial perturbations of neutron stars within a subclass of gauge-invariant Scalar-Vector-Tensor (SVT) theories. By solving the generalized Tolman-Oppenheimer-Volkoff (TOV) equations for several values of the modified gravity parameter, we examine the impact of the vector-curvature coupling on the structure and properties of neutron stars. We then extend our analysis by deriving the quadratic action governing linear radial perturbations and computing both the normal modes associated with the matter sector and the scalar quasinormal modes arising from the additional propagating degree of freedom of the theory, which is able to propagate outside the neutron star. Our results show that the modified gravity parameter can significantly affect the mass-radius relation, the oscillation spectrum, and the stability properties of neutron stars, while preserving the coincidence between the onset of radial instability and the maximum-mass configuration, as in General Relativity.