Quark-hadron crossover equations of state for neutron stars: constraining the chiral invariant mass in a parity doublet model

TL;DR

This paper develops a neutron star equation of state by interpolating hadronic and quark matter models, constraining the chiral invariant mass parameter using observational data on neutron star radii.

Contribution

It introduces a crossover model between hadronic and quark matter incorporating the parity doublet structure, linking the chiral invariant mass to neutron star properties.

Findings

Chiral invariant mass $m_0$ constrained between 600 and 900 MeV.

Neutron star radii are strongly correlated with $m_0$.

The model provides a unified EOS for neutron stars with observational constraints.

Abstract

We construct an equation of state (EOS) for neutron stars by interpolating hadronic EOS at low density and quark EOS at high density. A hadronic model based on the parity doublet structure is used for hadronic matter and a quark model of Nambu--Jona-Lasinio type is for quark matter. We assume crossover between hadronic matter and quark matter in the the color-flavor locked phase. The nucleon mass of the parity doublet model has a mass associated with the chiral symmetry breaking, and a chiral invariant mass $m_0$ which is insensitive to the chiral condensate. The value of $m_0$ affects the nuclear EOSs at low density, and has strong correlations with the radii of neutron stars. Using the constraint to the radius obtained by LIGO-Virgo and NICER, we find that $m_0$ is restricted as $600\,\mathrm{MeV}\lesssim m_0 \lesssim 900\,\mathrm{MeV}$.