The presence of a critical end point in the QCD phase diagram from the net-baryon number fluctuations

TL;DR

This paper investigates the presence of a critical end point in the QCD phase diagram using net-baryon number fluctuations within the PNJL model, showing nonmonotonic susceptibilities can occur without a CEP.

Contribution

It demonstrates that nonmonotonic behavior of susceptibilities does not necessarily indicate a critical end point in the QCD phase diagram.

Findings

Nonmonotonic susceptibilities can occur without a CEP.

Ratios of susceptibilities and sound velocity may distinguish scenarios.

Smoother behaviors suggest absence of a CEP.

Abstract

The net-baryon number fluctuations for three-flavor quark matter are computed within the Polyakov extended Nambu$-$Jona-Lasinio model. Two models with vanishing and nonvanishing vector interactions are considered. While the former predicts a critical end point (CEP) in the phase diagram, the latter predicts no CEP. We show that the nonmonotonic behavior of the susceptibilities in the phase diagram is still present even in the absence of a CEP. Therefore, from the nonmonotonic behavior of the susceptibilities solely, one cannot assume the existence of a CEP. We analyze other possible properties that may distinguish the two scenarios, and determine the behavior of the net-baryon number fluctuations and the velocity of sound along several isentropes, with moderate and small values. It is shown that the value of the susceptibilities ratios and the velocity of sound at two or three isentropic lines could possibly allow to distinguish both scenarios, a phase diagram with or without CEP. Smoother behaviors of these quantities may indicate the nonexistence of a CEP. We also discuss the critical behavior of the strange sector.