# The non-equilibrium attractor: Beyond hydrodynamics

## TL;DR

This paper discusses the concept of a non-equilibrium attractor in quark-gluon plasma evolution, explaining how solutions converge to this attractor despite the system not being in local thermal equilibrium, thus extending hydrodynamic descriptions.

## Contribution

It reviews recent work demonstrating the existence of a non-equilibrium attractor in kinetic theory models beyond traditional hydrodynamic moments.

## Key findings

- Existence of a non-equilibrium attractor in kinetic theory.
- Solutions converge to the attractor, indicating pseudo-thermalization.
- Hydrodynamics effectively describes the system after initial non-equilibrium phase.

## Abstract

The quark-gluon plasma created in heavy-ion collisions is not in local thermal equilibrium at early times. Despite this, dissipative hydrodynamics describes the evolution of the energy-momentum tensor quite well after only roughly 0.5 - 1 fm/c. This can be understood using the concept of a non-equilibrium dynamical attractor. The attractor is a uniquely identifiable solution to the dynamical equations to which all solutions are drawn as the system evolves. Once solutions collapse onto the non-equilibrium attractor they are ``pseudo-thermalized'' in the sense that they have lost information about the precise initial conditions used, but are not yet in exact local thermal equilibrium. Here I review recent work which demonstrates that there exists a non-equilibrium attractor in full kinetic theory models which goes beyond the usual low-order momentum moments considered in hydrodynamical treatments.