Far-from-Equilibrium Attractors and Universality in Ultra-Relativistic Heavy-Ion Collisions within Relativistic Kinetic Theory

TL;DR

This thesis investigates the emergence of attractors and universal behavior in ultra-relativistic heavy-ion collisions using relativistic kinetic theory, demonstrating that a few key variables can effectively describe system collectivity.

Contribution

It introduces a comprehensive analysis of attractors and universality in heavy-ion collisions within relativistic kinetic theory, extending from simple models to realistic scenarios.

Findings

Attractors and universality are observed across various models.

A few physical variables effectively characterize system collectivity.

The relativistic Boltzmann Transport model accurately describes collective behavior.

Abstract

This PhD Thesis is devoted to the study of the emergence of attractors, universality and collectivity in ultra-relativistic collisions by means of relativistic kinetic theory. After an introduction about Quantum Chromodynamics (QCD), Quark-Gluon Plasma (QGP) and the importance of heavy-ion collisions to investigate both, we give an overview about the two main models able to describe the hot QCD matter collective behaviour, namely kinetic theory and hydrodynamics. Afterwards, the Relativistic Boltzmann Transport (RBT) model, which has been employed to obtain most part of the results of this thesis, is carefully described, from the numerical and physical perspectives. The study of attractors and universality proceeds then by starting from a simple one-dimensional massless model, moving to increasingly more complex scenarios, involving the full 3+1D setup, non-conformal systems and realistic event-by-event fluctuations. Particular attention is paid to the physical scales which govern the system collectivity and their interplay. We show that a very good description of collective behaviour can be carried out by means of a few variables which characterise the systems under study.