Broad excitations in a 2+1D overoccupied gluon plasma

TL;DR

This study investigates nonperturbative excitations in a 2+1D overoccupied gluon plasma, revealing broad spectral features and the potential for an effective kinetic theory despite the absence of soft quasiparticles.

Contribution

It provides the first nonperturbative analysis of excitations in 2+1D gauge theories relevant to heavy-ion collisions, highlighting their broad spectral peaks and implications for kinetic descriptions.

Findings

Broad excitation peaks in spectral functions

Absence of soft quasiparticles in 2+1D

Long-lived high-momentum excitations

Abstract

Motivated by the initial stages of high-energy heavy-ion collisions, we study excitations of far-from-equilibrium 2+1 dimensional gauge theories using classical-statistical lattice simulations. We evolve field perturbations over a strongly overoccupied background undergoing self-similar evolution. While in 3+1D the excitations are described by hard-thermal loop theory, their structure in 2+1D is nontrivial and nonperturbative. These nonperturbative interactions lead to broad excitation peaks in spectral and statistical correlation functions. Their width is comparable to the frequency of soft excitations, demonstrating the absence of soft quasiparticles in these theories. Our results also suggest that excitations at higher momenta are sufficiently long-lived, such that an effective kinetic theory description for 2+1 dimensional Glasma-like systems may exist, but its collision kernel must be nonperturbatively determined.