Degrees of freedom and the phase transitions of two flavor QCD

TL;DR

This paper compares effective QCD models with and without Polyakov loop to understand phase transitions, emphasizing the Polyakov loop's role in accurately modeling thermodynamics at finite temperature and density.

Contribution

It demonstrates that including the Polyakov loop in effective models is essential for realistic predictions of QCD thermodynamics.

Findings

Polyakov loop inclusion improves model accuracy

Models match pure gauge theory thermodynamics

Finite density thermodynamics are analyzed

Abstract

We study two effective models for QCD, the Nambu-Jona-Lasinio -model and the linear sigma model extended by including a Polyakov loop potential, which is fitted to reproduce pure gauge theory thermodynamics, and a coupling between the chiral fields and the Polyakov loop. Thus the resulting models have as relevant degrees of freedom the Polyakov loop and chiral fields. By comparing the extended models with the bare chiral models we can conclude that the addition of the Polyakov loop is necessary in order to obtain both qualitatively and quantitatively correct results at finite temperatures. These results are extended to finite net quark densities, several thermodynamical quantites are investigated in detail and possible applications and consequences for relativistic heavy ion collision phenomenology are discussed.