# Early time dynamics and hard probes in heavy-ion collisions

## TL;DR

This paper reviews the current understanding of the early time dynamics in high-energy heavy-ion collisions, focusing on the initial state, pre-equilibrium phase, and their impact on hard probes, highlighting recent theoretical and phenomenological advances.

## Contribution

It provides a comprehensive overview of the microscopic and macroscopic descriptions of early time dynamics and introduces a novel macroscopic model of the pre-equilibrium phase.

## Key findings

- Pre-equilibrium phase influences final particle distributions.
- Weak-coupling models effectively describe early dynamics.
- Connections between initial state physics and hard probes are elucidated.

## Abstract

We present an overview of the current state of understanding of the early time dynamics of high-energy heavy-ion collisions, emphasizing recent developments and connections between the physics of the initial state and that of hard probes in heavy-ion collisions. Based on a weak-coupling description, we first establish a microscopic picture of the early time dynamics and equilibration process and subsequently discuss their macroscopic manifestations along with a novel macroscopic description of the pre-equilibrium phase. Some phenomenological consequences concerning the role of the pre-equilibrium phase in large (AA) and small (pp/pA) collision systems are briefly discussed along with open questions and opportunities for future improvements.