Net-baryon number variance and kurtosis within nonequilibrium chiral fluid dynamics

TL;DR

This paper investigates how fluctuations in net-baryon number, including variance and kurtosis, behave near phase transitions in a QCD-inspired fluid dynamical model, highlighting divergence and enhancement effects.

Contribution

It introduces a nonequilibrium chiral fluid dynamics model that captures spinodal instabilities and their impact on baryon number fluctuations during heavy-ion collisions.

Findings

Diverging quark number susceptibility along spinodal lines.

Enhanced baryon number fluctuations at the critical point.

Distinct fluctuation patterns during first-order transition versus crossover.

Abstract

We study the variance and kurtosis of the net-baryon number in a fluid dynamical model for heavy-ion collisions. It is based on an effective chiral model with dilatons for the strong coupling regime of QCD. Taking into account spinodal instabilities, we demonstrate that this model exhibits a diverging quark number susceptibility and kurtosis all along the spinodal lines of the first-order phase transition, with a change of universality class at the critical end point. During the (3+1) dimensional expansion of a hot and dense fireball, instabilities are created by fluctuations in the explicitly propagated chiral and dilaton field. We find a clear enhancement of event-by-event fluctuations of the baryon number at the critical point and first-order phase transition in comparison with an evolution through the crossover region.