Non-Gaussian hydrodynamic fluctuations in an expanding relativistic fluid

TL;DR

This paper derives and solves evolution equations for non-Gaussian velocity fluctuations in an expanding relativistic fluid, highlighting the significance of non-linear and memory effects for QCD critical point searches.

Contribution

It introduces a framework for analyzing non-Gaussian hydrodynamic fluctuations in relativistic expansion using effective field theory and provides analytical solutions.

Findings

Three-point correlators depend nonlinearly on two-point functions.

Memory effects influence non-Gaussian fluctuations.

The average Landau frame aligns with the density frame in Bjorken flow.

Abstract

We consider non-equilibrium evolution of non-Gaussian fluctuations in a hydrodynamic system undergoing a boost-invariant expansion described by Bjorken flow. We derive the evolution equations for two- and three-point velocity correlators using the effective field theory framework and present analytical solutions for them. We show that the average Landau frame is better suited for studying non-Gaussian fluctuations of velocity when relativistic effects are important. In the Bjorken background, the average Landau frame corresponds to the density frame. We demonstrate that the three-point correlators depend nonlinearly on the non-equilibrium dynamics of the two-point functions, and exhibit non-trivial effects such as memory. The importance of these effects in the context of the search for the QCD critical point via fluctuations is discussed.