Off-equilibrium non-Gaussian fluctuations near the QCD critical point: an effective field theory perspective

TL;DR

This paper develops an effective field theory framework to describe off-equilibrium non-Gaussian fluctuations of baryon density near the QCD critical point, aiding experimental searches in heavy-ion collisions.

Contribution

It introduces a systematic dynamical EFT approach to model real-time non-Gaussian fluctuations and derives evolution equations for density correlators in off-equilibrium conditions.

Findings

Non-linear noise interactions can influence quartic fluctuations.

Derived closed-form solutions for multi-point correlators.

Potential impact on interpreting experimental fluctuation data.

Abstract

The non-Gaussian fluctuations of baryon density are sensitive to the presence of the conjectured QCD critical point. Their observational consequences are crucial for the ongoing experimental search for this critical point through the beam energy scan program at Relativistic Heavy Ion Collider (RHIC). In the expanding fireball created in a heavy-ion collision, critical fluctuations would inescapably fall out of equilibrium, and require a systematic description within a dynamical framework. In this paper, we employ newly developed effective field theory (EFT) for fluctuating hydrodynamics to study the real-time critical non-Gaussian fluctuations of a conserved charge density. In particular, we derive the evolution equations for multi-point correlators of density fluctuations and obtain the closed-form solutions with arbitrary initial conditions that can readily be implemented in realistic simulations for heavy-ion collisions. We find that non-linear interactions among noise fields, which are missing in traditional stochastic hydrodynamics, could potentially contribute to the quartic (fourth order) fluctuations in scaling regime even at tree level in off-equilibrium situations.