Speaker
Description
Motivated by the early-time dynamics of the quark-gluon plasma in high-energy heavy-ion collisions, we study spectral excitations of overoccupied gauge theories far from equilibrium using classical-statistical lattice simulations. 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. Their width is comparable to the frequency of soft excitations, demonstrating the absence of soft quasiparticles in these theories. Our results thus suggest that effective kinetic theory descriptions of such 2+1D systems require collision kernels that must be nonperturbatively determined.
