Broad excitations in a 2+1D overoccupied gluon plasma

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.

The imaginary part of the heavy-quark potential from real-time Yang-Mills dynamics

“…Such non-equilibrium extractions are necessary since it is currently unknown how to analytically extract the heavy-quark potential in anisotropic plasmas due the presence of a non-Abelian plasma instability called the chromo-Weibel instability [25,[61][62][63][64]. In particular, recent studies have shown that particularly in highly anisotropic systems nonperturbative effects beyond hard loop calculations are crucial [65,66].…”

Spectral function of fermions in a highly occupied non-Abelian plasma

“…One also observes from Fig. 5 that the fermion damping rate γ + (p) decreases monotonically as a function of momentum, which is qualitatively different from gluonic spectral functions in non-equilibrium overoccupied plasmas, where a monotonically increasing damping rate has been observed [17,18].…”

“…This algorithm is completely analogous to the one for the gluon spectral function developed in [17,18]. One initializes a fluctuation in a specific momentum mode, evolves forward in time in coordinate space, and projects back to the momentum state after the evolution.…”

“…We note that this procedure is analogous to the linear response framework employed in Refs. [17,18,35] to extract the gluon spectral function, where similarly, one fixed Coulomb gauge and subsequently studies the response of the gauge fields to plane wave perturbations in order to extract the spectral function.…”

“…The purpose of this paper is to compute this spectral function. Based on earlier calculations of spectral functions for gluons [17,18] and the real time lattice fermion code developed in [19,20], we will first develop a numerical method to calculate the spectral function in an out-of-equilibrium overoccupied background gauge field configuration. We are studying fermion interactions with a strongly overoccupied gluon field, thus the dynamics is dominated by gluons and the physical situation is very different from systems at large baryon density (see, e.g., recent work in [21]).…”