Study of Neutron Star Properties under the Two-Flavor Quark NJL Model

TL;DR

This paper models neutron star matter using a hybrid approach combining hadronic and quark matter models, revealing that early quark percolation is essential to match observational constraints.

Contribution

It introduces a thermodynamically consistent crossover between hadronic and quark phases in neutron star modeling, reconciling various observational data.

Findings

Early quark percolation near nuclear saturation density is necessary.

The model can satisfy both high-mass pulsar and radius constraints.

A smooth crossover improves the physical consistency of the EOS.

Abstract

The Equation of State (EOS) of matter within neutron stars is a central topic in nuclear physics and astrophysics.This study investigates hadron-quark hybrid stars by integrating the density-dependent DDME2 relativistic mean-field model for hadronic matter with a two-flavor Nambu-Jona-Lasinio (NJL) model for quark matter.A quintic polynomial interpolation is employed to construct a smooth ($C^2$ continuity) and thermodynamically consistent crossover between the phases.We systematically explore the parameter space to reconcile the tension between the high stiffness required by massive pulsars and the softness demanded by tidal deformability and radius constraints.Our analysis demonstrates that to simultaneously satisfy the mass measurement of PSR J0740+6620 and the compact radius constraints from NICER (e.g., PSR J0437-4715), the hadron-quark crossover must initiate in the vicinity of nuclear saturation density.This result suggests that the early percolation of quark degrees of freedom is a necessary feature to accommodate current multi-messenger observations.