The strongly interacting Quark Gluon Plasma, and the critical behaviour of QCD at imaginary chemical potential

TL;DR

This paper investigates the critical behavior of the QCD phase diagram near the transition temperature using imaginary chemical potential to avoid the sign problem, revealing insights into the strongly interacting quark-gluon plasma and its complex properties.

Contribution

It provides the first detailed analysis of QCD critical behavior at imaginary chemical potential, extending understanding of the strongly interacting quark-gluon plasma beyond previous zero chemical potential studies.

Findings

Evidence of critical behavior near the transition line in the negative mu^2 plane.

Analytic continuation of results does not match existing phenomenological models.

Demonstrates the importance of the complex nature of the functional integral measure.

Abstract

We explore the highly non-perturbative hot region of the QCD phase diagram close to Tc by use of an imaginary chemical potential mu which avoids the sign problem. The number density and the quark number susceptibility are consistent with a critical behaviour associated with the transition line in the negative mu^2 half-plane. We compare the analytic continuation of these results with various phenomenological models, none of which provides a satisfactory description of data, a failure on which we make some comments. These results complement and extend the information obtained via the analysis of the susceptibilities evaluated at zero mu, yielding a simple description of the candidate strongly interacting QGP phase. As a byproduct of our analysis we investigate the Polyakov loop and its hermitian conjugate. Our data offer a vivid evidence of the importance of the complex nature of the functional integral measure, which results in L (mu) ne \bar L(mu) for a real chemical potential.