Multiple Critical Points in Effective Quark Models

TL;DR

This paper investigates the phase structure of effective quark models beyond mean field, revealing multiple critical points and analyzing their physical nature to reconcile model predictions with lattice results.

Contribution

It demonstrates the existence of multiple critical points in the Linear Sigma and Nambu Jona-Lasinio models beyond mean field approximation.

Findings

Multiple critical points can occur in these models.

A new high-temperature, low-density critical point is identified.

The new first order line has a more chiral character.

Abstract

We consider the two flavor version of the Linear Sigma Model as well as of the Nambu Jona-Lasinio model, at finite temperature and quark chemical potential, beyond the Mean Field Approximation. Using parameter values for the pion and quark current masses which weakly break chiral symmetry we show that both models can present more than one critical end point. In particular, we explicitly show that the appearance of a new critical point associated with a first order line at high temperature and low densities could help to conciliate some lattice results with model predictions. Using different techniques, we perform an extensive thermodynamical analysis to understand the physical nature of the different critical points. For both models, our results suggest that the new first order line which starts at vanishing chemical potential has a more chiral character than the usual line which displays a character more reminiscent of a liquid-gas phase transition.