Abstract
We extract the heavy-quark diffusion coefficient κ and the resulting momentum broadening 〈p2〉 in a far-from-equilibrium non-Abelian plasma. We find several features in the time dependence of the momentum broadening: a short initial rapid growth of 〈p2〉, followed by linear growth with time due to Langevin-type dynamics and damped oscillations around this growth at the plasmon frequency. We show that these novel oscillations are not easily explained using perturbative techniques but result from an excess of gluons at low momenta. These oscillation are therefore a gauge invariant confirmation of the infrared enhancement we had previously observed in gauge-fixed correlation functions. We argue that the kinetic theory description of such systems becomes less reliable in the presence of this IR enhancement.
Highlights
Medium are created in the hard processes preceding the formation of the QGP
We find several features in the time dependence of the momentum broadening: a short initial rapid growth of p2, followed by linear growth with time due to Langevin-type dynamics and damped oscillations around this growth at the plasmon frequency
We present our numerical results for the evolution of the heavy-quark diffusion coefficient κ∞(t) and the correlator κ (t, ∆t) and compare them to results using the spectral reconstruction (SR) and Kinetic theory (KT) methods introduced in the previous section
Summary
The system we are studying is described by an SU(2) pure gauge theory. Its classical evolution starts from an initial condition that is characterised by a single-particle occupation number distribution f At momenta p ωpl we observed in our earlier work that the actual occupation number distribution [72] displays a feature that we refer to as an “IR enhancement,” a feature seen in earlier studies (see, e.g., [48, 57]) By this term we mean that the occupation number is significantly larger than the behavior f (p) ∼ T∗/p expected from perturbation theory. A gauge theory with a non-conserved number of particles is not expected to exhibit actual condensation (see, e.g., [48, 75, 77]), and we do not interpret this excess of gluons as an indication of condensation in the proper sense of the word. We vary as and Ns to check for possible lattice artifacts (see appendix A)
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