# The First fm/c of Heavy-Ion Collisions

## TL;DR

This paper reviews the early non-equilibrium dynamics of high-energy heavy-ion collisions, focusing on the thermalization processes of the quark-gluon plasma within the first femtometer per c, using weak coupling theoretical tools.

## Contribution

It provides a comprehensive overview of the theoretical understanding of thermalization mechanisms in the early stages of heavy-ion collisions, highlighting progress in weakly coupled QCD plasma studies.

## Key findings

- Progress in understanding thermalization mechanisms
- Insights into the approach to local thermal equilibrium
- Connections to heavy-ion collision phenomenology

## Abstract

We present an introductory review of the early time dynamics of high-energy heavy-ion collisions and the kinetics of high temperature QCD. The equilibration mechanisms in the quark-gluon plasma uniquely reflect the non-abelian and ultra-relativistic character of the many body system. Starting with a brief expose of the key theoretical and experimental questions, we provide an overview of the theoretical tools employed in weak coupling studies of the early time non-equilibrium dynamics. We highlight theoretical progress in understanding different thermalization mechanisms in weakly coupled non-abelian plasmas, and discuss their relevance in describing the approach to local thermal equilibrium during the first ${\rm fm}/c$ of a heavy-ion collision. Some important connections to the phenomenology of heavy-ion collisions are also briefly discussed.