Isotropization of a rotating and longitudinally expanding $\phi^4$ scalar system

TL;DR

This paper uses numerical simulations to study how a rotating, expanding massless scalar field system with quartic interactions becomes isotropic over time, focusing on the decay of angular momentum and pressure anisotropy.

Contribution

It provides the first detailed numerical analysis of isotropization and angular momentum decay in a rotating scalar field system with expansion.

Findings

Angular momentum decays faster than pressure anisotropy.

System approaches isotropy on a shorter timescale than angular momentum loss.

Rotational effects diminish significantly during expansion.

Abstract

We present numerical simulations for the evolution of an expanding system of massless scalar fields with quartic coupling. By setting a rotating, non-isotropic initial configuration, we compute the energy density, the transverse and longitudinal pressures and the angular momentum of the system. We compare the time scales associated with the isotropization and the decay of the initial angular momentum due to the expansion, and show that even for fairly large initial angular momentum, it decays significantly faster than the pressure anisotropy.