  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.
