Constraining the competition between the deconfinement and chiral phase transitions in light of the multimessenger era

TL;DR

This paper investigates the interplay between chiral symmetry restoration and deconfinement in neutron star cores using extended models, finding stable hybrid stars with masses up to about 2.2 solar masses consistent with observations.

Contribution

It introduces a systematic study of the competition between chiral and deconfinement phase transitions in neutron stars using combined parity doublet and NJL models with a Maxwell construction.

Findings

Stable neutron stars with quark cores are possible within certain parameter ranges.

The maximum hybrid star mass reaches approximately 2.2 solar masses.

A larger chiral invariant mass and a bigger split between phase transitions are favored by observations.

Abstract

We extend the parity doublet model for hadronic matter and study the possible presence of quark matter inside the cores of neutron stars with the Nambu-Jona-Lasinio (NJL) model. Considering the uncertainties of the QCD phase diagram and the location of the critical endpoint, we aim to explore the competition between the chiral phase transition and the deconfinement phase transition systematically, regulated by the vacuum pressure $-B$ in the NJL model. Employing a Maxwell construction, a sharp first-order deconfinement phase transition is implemented combining the parity doublet model for the hadronic phase and the NJL model for the high-energy quark phase. The position of the chiral phase transition is obtained from the NJL model self-consistently. We find stable neutron stars with a quark core within a specific parameter space that satisfies current astronomical observations. The observations suggest a relatively large chiral invariant mass $m_0=600$ MeV in the parity doublet model and a larger split between the chiral and deconfinement phase transitions while assuming the first-order deconfinement phase transition. The maximum mass of the hybrid star that we obtain is $\sim 2.2 M_{\odot}$.