Towards a fluid-dynamic description of an entire heavy-ion collision: from the colliding nuclei to the quark-gluon plasma phase

TL;DR

This paper investigates whether second-order fluid dynamics can effectively model the initial, far-from-equilibrium stages of heavy-ion collisions, aiming to unify the description from nuclei collision to quark-gluon plasma formation.

Contribution

It explores the feasibility of using second-order relativistic fluid theory to describe the initial collision phase and sets the groundwork for a comprehensive dynamical model of heavy-ion collisions.

Findings

Initial conditions can be derived from second-order fluid dynamics.

Entropy production during early stages can be quantified.

A pathway to a unified collision model is outlined.

Abstract

The fluid-dynamical modeling of a nuclear collision at high energy usually starts shortly after the collision. A major source of uncertainty comes from the detailed modeling of the initial state. While the collision itself likely involves far-from-equilibrium dynamics, it is not excluded that a fluid theory of second order can reasonably well describe its soft features. Here we explore this possibility and discuss how the state before the collision can be described in that setup, what are the requirements from relativistic causality to the form of the equations of motion, how much entropy production can result from shear and bulk viscous dissipation during the initial longitudinal dynamics, and how one can thus obtain sensible initial conditions for the subsequent transverse expansion. While we do here only first steps, we outline a larger program. If the latter could be successfully completed it could lead to a dynamical description of heavy-ion collisions where the only uncertainty lies in the thermodynamic and transport properties of quantum chromodynamics.