Quark-hadron crossover equations of state for neutron stars: Constraining the chiral invariant mass in a parity doublet model
Takuya Minamikawa, Toru Kojo, Masayasu Harada
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 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 $600\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}\ensuremath{\lesssim}{m}_{0}\ensuremath{\lesssim}900\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$.