# Isovector Effects in Neutron Stars, Radii and the GW170817 Constraint

## TL;DR

This paper investigates how including an isovector-scalar meson in nuclear matter models affects neutron star properties, using GW170817 data to constrain the model and exploring implications for radii, masses, and tidal deformability.

## Contribution

It introduces a self-consistent incorporation of the isovector-scalar meson into the quark-meson coupling model and assesses its impact on neutron star structure and observational constraints.

## Key findings

- Isovector-scalar force significantly influences neutron star radii and masses.
- Inclusion of this force surpasses uncertainties from symmetric nuclear matter parameters.
- Model predictions align with GW170817 constraints on tidal deformability.

## Abstract

An isovector-scalar meson is incorporated self-consistently into the quark-meson coupling description of nuclear matter and its most prominent effects on the structure of neutron stars are investigated. The recent measurement of GW170817 is used to constrain the strength of the isovector-scalar channel. With the imminent measurements of the neutron star radii in the NICER mission it is particularly notable that the inclusion of the isovector-scalar force has a significant impact. Indeed, the effect of this interaction on the neutron star radii and masses is larger than the uncertainties introduced by variations in the parameters of symmetric nuclear matter at saturation, namely the density, binding energy per nucleon and the symmetry energy. In addition, since the analysis of GW170817 has provided constraints on the binary tidal deformability of merging neutron stars, the predictions for this parameter within the quark-meson coupling model are explored, as well as the moment of inertia and the quadrupole moment of slowly rotating neutron stars.