# Axial quasi-normal modes of scalarized neutron stars with massive self-interacting scalar field

## TL;DR

This paper investigates how massive, self-interacting scalar fields affect the axial quasi-normal modes of neutron stars, extending universal relations known in general relativity to scalar-tensor theories with various realistic equations of state.

## Contribution

It extends the universal relations for neutron star axial quasi-normal modes to include massive scalar-tensor theories with self-interaction, considering multiple realistic equations of state.

## Key findings

- Universal relations hold in massive scalar-tensor theories.
- Scalarization effects can cause large deviations from general relativity.
- Massive scalar fields are less constrained by observations, allowing significant deviations.

## Abstract

We study the axial quasi-normal modes of neutron stars in scalar-tensor theories with massive scalar field including a self-interacting term in the potential. Various realistic equations of state including nuclear, hyperonic and hybrid matter are employed. Although the effect of spontaneous scalarization of neutron stars can be very large, binary pulsar observations and gravitational wave detections significantly constrain the massless scalar-tensor theories. If we consider a properly chosen nonzero mass for the scalar field, though, the scalar-tensor parameters cannot be restricted by the observations, resulting in large deviation from pure general relativity. With this motivation in mind, we extend the universal relations for axial quasi-normal modes known in general relativity to neutron stars in massive scalar-tensor theories with self-interaction using a wide range of realistic EOS. We confirm the universality of the scaled frequency and damping time in terms of the compactness and scaled moment of inertia for neutron stars with and without massive scalarization.