Study of hybrid stars with nonstrange quark matter cores

TL;DR

This study explores the existence of nonstrange quark matter cores in hybrid stars using a modified NJL model constrained by lattice QCD, and compares the resulting star properties with recent astrophysical observations.

Contribution

It introduces a modified coupling in the 2-flavor NJL model to analyze nonstrange hybrid stars, constrained by lattice QCD data, and assesses their compatibility with neutron star measurements.

Findings

Pure nonstrange quark cores can exist in hybrid stars.

Maximum hybrid star mass is about 0.1 solar mass less than in the conventional NJL model.

Binary neutron stars in GW170817 are likely hadron stars.

Abstract

In this work, under the hypothesis that quark matter may not be strange (Holdom et al. 2018), we adopt a modification of the coupling constant of the four-quark scalar interaction $G\rightarrow G_1+G_2\langle\bar{\psi}\psi\rangle$ in the 2-flavor Nambu-Jona-Lasinio (NJL) model to study nonstrange hybrid stars, where $G_1$ and $G_2$ are two parameters constrained by using the lattice QCD simulation results at the critical temperature and zero chemical potential. The Maxwell construction is used to describe the first-order confinement-deconfinement phase transition in hybrid stars. With recent measurements on neutron star mass, radius, and tidal deformability, the hybrid equation of states are constrained. It is found that pure nonstrange quark matter cores can exist in hybrid stars, possessing $0.026-0.04$ solar mass. The maximum hybrid star mass in the framework of the modified NJL model is about 0.1 solar mass lighter than that in the conventional 2-flavor NJL model. It is argued that the binary neutron stars in GW170817 should be hadron stars.