Toward Identifying the QCD Critical Point: attenuation of the sound mode around the critical point

TL;DR

This paper investigates how relativistic effects influence density fluctuations near the QCD critical point, suggesting that attenuation of sound modes could serve as an experimental signal for its detection in heavy-ion collisions.

Contribution

It provides a relativistic fluid dynamics analysis of density fluctuations around the QCD critical point, highlighting the attenuation of sound modes as a potential observable.

Findings

Relativistic effects modify the width of sound and thermal modes.

Density fluctuations are attenuated near the QCD critical point.

Suppression of Mach cones could signal the QCD critical point.

Abstract

Motivated by the fact that QCD critical point (CP) belongs to the same universality class as the liquid-gas transition, the dynamical density fluctuations around the CP is analyzed using relativistic fluid dynamics for a viscous fluid. It is shown that relativistic effects on the dynamical structure factor of the density fluctuation appears only in the width of the sound and thermal modes through a modification of the transport/kinetic coefficients. It is found that the mechanical density fluctuation which is enhanced by the relativistic effects are attenuated, whereas the entropy fluctuation in turn becomes more prominent around the QCD CP. This attenuation of the density fluctuation around the QCD CP may imply that if the suppression or even total disappearance of Mach cone is observed as the incident energy of the relativistic heavy-ion collisionsis lowered, it can be a signal of the existence of the QCD critical point.