Speed of sound, breaking of conformal limit and instabilities in quark-gluon plasma at finite baryon density

TL;DR

This paper investigates the properties of quark-gluon plasma at finite baryon density, revealing how the speed of sound approaches or exceeds the conformal limit and identifying instabilities linked to the Polyakov loop behavior.

Contribution

It provides a detailed analysis of the quark-gluon plasma's thermodynamics at finite density using the Field Correlator Method, highlighting the conditions under which conformal limit violations and instabilities occur.

Findings

At low densities, QGP thermodynamics matches lattice data.

Speed of sound remains below or equal to 1/3 at low densities.

For chemical potential > 0.5 GeV, the speed of sound exceeds the conformal limit, indicating instabilities.

Abstract

The properties of the quark-gluon plasma(QGP) in the presence of baryon chemical potential are studied using the Field Correlator Method(FCM). At low densities the QGP thermodynamics with the colormagnetic confinement and the Polyakov line interaction is in good agreement with lattice data,and the speed of sound satisfies $C_s^2\leq \frac13$,but in the intermediate range of densities the speed of sound displays a singular behaviour and one needs density modifications of the Polyakov line interaction to avoid instabilities. In particular for $\mu_q >0.5$ GeV there exists a region in the $(\mu, T)$ plane where $C^2_s$ violates the conformal limit. This behaviour is strongly connected to the properties of the Polyakov loop and its density dependence.