Heavy quark diffusion in an overoccupied gluon plasma

<!--HTML-->We extract the heavy-quark diffusion coefficient $\kappa$ and the resulting momentum broadening $\langle p^2 \rangle$ in an overoccupied gluon plasma. We find several features in the time dependence of the momentum broadening: a short initial rapid growth of $\langle p^2 \rangle$ followed by linear growth in time due to Langevin-type dynamics and damped oscillations around this growth at the plasmon frequency. We show that these oscillations arise from an excess of gluons in the infrared and are therefore a gauge invariant confirmation of the infrared enhancement we have previously observed in gauge-fixed correlation functions. We argue that the kinetic theory description becomes less reliable in the presence of this IR enhancement.