# Paths to equilibrium in non-conformal collisions

## TL;DR

This paper investigates the sequence of relaxation processes in non-conformal holographic heavy ion collisions, revealing that different relaxation times can occur in various orders and that the velocity field remains nearly boost-invariant at hydrodynamization.

## Contribution

It provides a detailed numerical analysis of multiple relaxation times in non-conformal theories and explores their ordering and implications for heavy ion collision modeling.

## Key findings

- Condensate can remain far from equilibrium after hydrodynamization.
- Rapidity distribution width decreases with increasing non-conformality.
- Velocity field at hydrodynamization is nearly boost-invariant regardless of non-conformality.

## Abstract

We extend our previous analysis of holographic heavy ion collisions in non-conformal theories. We provide a detailed description of our numerical code. We study collisions at different energies in gauge theories with different degrees of non-conformality. We compare four relaxation times: the hydrodynamization time (when hydrodynamics becomes applicable), the EoSization time (when the average pressure approaches its equilibrium value), the isotropization time (when the longitudinal and transverse pressures approach each other) and the condensate relaxation time (when the expectation value of a scalar operator approaches its equilibrium value). We find that these processes can occur in several different orderings. In particular, the condensate can remain far from equilibrium even long after the plasma has hydrodynamized and EoSized. We also explore the rapidity distribution of the energy density at hydrodynamization. This is far from boost-invariant and its width decreases as the non-conformality increases. Nevertheless, the velocity field at hydrodynamization is almost exactly boost-invariant regardless of the non-conformality. This result may be used to constrain the initialization of hydrodynamic fields in heavy ion collisions.