Nonperturbative excitations in overoccupied gluon plasmas

TL;DR

This paper investigates the nonperturbative excitations in overoccupied gluon plasmas using lattice simulations, revealing perturbative behavior in 3+1 dimensions and nonperturbative effects in 2+1 dimensions relevant to heavy-ion collision phenomenology.

Contribution

It provides the first detailed spectral function analysis of overoccupied gauge theories far from equilibrium in different dimensions, highlighting nonperturbative effects.

Findings

Spectral functions in 3+1D show quasiparticles consistent with perturbative predictions.

In 2+1D, excitations are broad and nonperturbative, lacking soft quasiparticles.

Results suggest significant nonperturbative corrections in systems with large momentum anisotropy.

Abstract

Motivated by the early-time dynamics of the quark-gluon plasma in high-energy heavy-ion collisions, we extract gluonic spectral functions of overoccupied gauge theories far from equilibrium using classical-statistical lattice simulations and linear response theory. In 3+1 dimensions we find that the spectral function exhibits quasiparticle excitations at all momenta that are mostly consistent with perturbative hard-thermal loop predictions, while partially showing nonperturbative deviations. In contrast, the structure of excitations in 2+1 dimensions is nontrivial and nonperturbative. These nonperturbative interactions lead to broad excitation peaks in the spectral function, demonstrating the absence of soft quasiparticles in these theories. This also suggests that there may be significant nonperturbative corrections present in systems with large momentum anisotropy, which are relevant to phenomenological applications in heavy-ion collisions.