Non-Equilibrium Dynamics in QCD and Holography

TL;DR

This paper reviews how holographic models help understand non-equilibrium dynamics in QCD-like plasmas, focusing on shear viscosity, sound waves, and chiral magnetic effects during heavy ion collisions.

Contribution

It introduces three holographic approaches to study non-equilibrium phenomena in QCD, bridging effective hydrodynamics with full non-equilibrium holographic descriptions.

Findings

Holography provides insights into shear viscosity during non-equilibrium.

Propagation of non-equilibrium sound waves can be modeled holographically.

Holographic methods reveal the non-equilibrium chiral magnetic effect.

Abstract

The plasma generated in heavy ion collisions goes through different phases in its time evolution. While early times right after the collision are governed by far-from equilibrium dynamics, later times are believed to be well described by near-equilibrium dynamics. While the regimes of non-equilibrium are prohibitively complicated to describe within QCD, effective descriptions such as hydrodynamics provide a viable approach. In addition, holographic descriptions allow access to the full non-equilibrium dynamics at strong coupling. In this presentation, we review three examples of such hydrodynamic approaches and corresponding holographic descriptions: 1) non-equilibrium shear viscosity, 2) propagation of non-equilibrium sound waves, and 3) the non-equilibrium chiral magnetic effect.