Nonstrange and strange quark matter at finite temperature within modified NJL model and protoquark stars

TL;DR

This paper extends a modified NJL model to finite temperatures to study protoquark stars, revealing how exchange interactions influence phase transitions and the equation of state, with implications for stellar properties.

Contribution

It introduces finite temperature effects into the modified NJL model with exchange interactions and analyzes their impact on protoquark star properties and phase transitions.

Findings

Exchange interactions change the phase transition from first-order to crossover.

The EOS becomes significantly stiffer in the crossover regime.

Finite temperature and lepton fraction have limited effects on the EOS.

Abstract

We extend the modified Nambu-Jona-Lasinio (NJL) model -- incorporating exchange interactions via the Fierz transformation -- to finite temperatures in both two- and three-flavor scenarios, and investigate the properties of protoquark stars in $\beta$-equilibrium. Our results show that increasing the strength of exchange interactions, characterized by the parameter $\alpha$, changes the chiral phase transition from first-order to crossover. We examine the effects of finite temperature, lepton fraction, and exchange interactions on the equation of state (EOS). We find that, in the crossover regime, the EOS is significantly stiffer than in the first-order case due to the substantial contribution of repulsive interactions in the exchange channels, while it remains relatively insensitive to variations in temperature and lepton fraction. Imposing the thermodynamic consistency, which requires the minimum of free energy per baryon $f / \rho_B$ occurs at zero pressure, further constrains the minimum value of vacuum pressure.