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 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 $600\mathrm{MeV}\lesssim m_0\lesssim 900\mathrm{MeV}$.

• Received 11 December 2020
• Accepted 29 March 2021

DOI:https://doi.org/10.1103/PhysRevC.103.045205