$\phi$-modes of neutron stars in a massless scalar-tensor theory

TL;DR

This paper investigates the scalar-led quasinormal modes of neutron stars in a massless scalar-tensor theory, revealing unique mode spectra and universal relations across different equations of state.

Contribution

It introduces the scalar-led $$-modes for neutron stars in a Brans-Dicke type scalar-tensor theory and compares them with general relativity, highlighting new spectral features.

Findings

Identification of scalar-led $$-modes for $l=0,1,2$

Comparison with general relativity scalar fields

Universal relations across equations of state

Abstract

Scalar-tensor theories allow for a rich spectrum of quasinormal modes of neutron stars. The presence of the scalar field allows for polar monopole and dipole radiation, as well as for additional higher multipole modes led by the scalar field. Here we present these scalar-led $\phi$-modes for the lowest multipoles, $l=0$, 1 and 2 for a massless scalar-tensor theory of the Brans-Dicke type, motivated by $R^2$ theory, and compare with those of a minimally coupled scalar field in general relativity. We consider a set of six realistic equations of state and extract universal relations for the modes.