Fluctuations and isentropes near the chiral critical endpoint

TL;DR

This study investigates how isentropic trajectories behave near the chiral critical endpoint using an effective chiral model, comparing mean-field and renormalization group approaches to understand the impact of fluctuations.

Contribution

It demonstrates that fluctuations significantly alter the shape of isentropic trajectories near the CEP, challenging previous conjectures about their focusing behavior.

Findings

Mean-field calculations show modified isentropes near the CEP.

Renormalization group results produce smooth isentropes unaffected by the CEP.

No focusing of isentropes towards the CEP is observed with proper fluctuations.

Abstract

Isentropic trajectories crossing the chiral phase transition near the critical endpoint (CEP) are studied for two light quark flavors. The calculations are performed within an effective chiral model with quark-meson interactions, belonging to the same universality class as QCD. We confront mean-field thermodynamics with the functional renormalization group approach, where fluctuations are properly taken into account. We establish a connection between modifications of the isentropic trajectories found in mean-field calculations at the crossover transition near the CEP and the order of the phase transition in the chiral limit. Furthermore, the isentropes obtained with the renormalization group are completely smooth at the crossover transition and do not in any way reflect the proximity of the CEP. In particular, our results do not show the recently conjectured focussing of isentropes from the crossover region towards the critical endpoint.