Hybrid stars with large quark cores within the parity doublet model and modified NJL model

TL;DR

This study explores the existence of hybrid neutron stars with large quark cores using parity doublet and modified NJL models, finding stable configurations consistent with observations and gravitational wave data.

Contribution

It introduces a combined approach with PDM and modified NJL models to analyze quark cores in neutron stars, highlighting conditions for stability and large quark cores.

Findings

Stable neutron stars with quark cores are possible within certain parameters.

Hybrid stars can have quark cores exceeding 1 solar mass.

Maximum hybrid star mass is approximately 2.2 solar masses.

Abstract

Using the parity doublet model (PDM) for hadronic matter and a modified Nambu-Jona-Lasinio (NJL) model for quark matter, we investigate the potential existence of two- and three-flavor quark matter in neutron star cores. Both models respect chiral symmetry, and a sharp first-order phase transition is implemented via Maxwell construction. We find stable neutron stars with quark cores within a specific parameter space that satisfies current astronomical observations. Typical neutron stars with masses around $1.4 \ M_\odot$ may possess deconfined quark matter in their centers. The hybrid star scenario with a two-flavor quark core offers enough parameter space to allow the neutron stars with large quark cores exceeding $\sim 1\ M_\odot$, and allow the early deconfinement position before $2\ \rho_0$, where $\rho_0$ is the nuclear saturation density. The observations of gravitational wave event GW170817 suggest a relatively large chiral invariant mass $m_0=600\ \rm MeV$ in the PDM for scenarios involving three-flavor quark matter cores. The maximum mass of the hybrid star with a quark core is found to be approximately $2.2\ M_\odot$ for both two- or three-flavor quark matter in their centers.