Broadening of the chiral critical region in a hydrodynamically expanding medium

TL;DR

This paper explores how higher cumulants of the sigma field, as the chiral order parameter, behave near the QCD phase transition, revealing a broadening of the critical region in an expanding medium similar to heavy-ion collisions.

Contribution

It introduces a thermodynamic approach to compute higher cumulants of the sigma field and demonstrates the broadening of the critical region in a hydrodynamically expanding medium.

Findings

Significant broadening of the critical region in an expanding medium.

Derived expressions for skewness and kurtosis from susceptibilities.

Comparison between static and expanding media shows enhanced critical fluctuations.

Abstract

We investigate higher cumulants of the sigma field as the chiral order parameter at the QCD phase transition. We derive a thermodynamic expression for the skewness and kurtosis from susceptibilities and use these to determine $S\sigma$ and $\kappa\sigma^2$ for the sigma field in equilibrium. In a next step, we study the behavior of these cumulants in both an equilibrated static medium and an expanding medium resembling the hydrodynamic stage of a heavy-ion collision. For the latter one, we find a significant broadening of the critical region.