Diffusion in an Expanding Plasma using AdS/CFT

We consider the diffusion of a non-relativistic heavy quark of fixed mass M, in a one-dimensionally expanding and strongly coupled plasma using the AdS/CFT duality. The Greens function constructed around a static string embedded in a background with a moving horizon, is identified with the noise correlation function in a Langevin approach. The (electric) noise decorrelation is of order 1/T(tau) while the velocity de-correlation is of order MD(tau)/T(tau). For MD>1, the diffusion regime is segregated and the energy loss is Langevin-like. The time dependent diffusion constant D(tau) asymptotes its adiabatic limit 2/pisqrt{lambda} T(tau) when tau/tau_0=(1/3eta_0tau_0)^3 where eta_0 is the drag coefficient at the initial proper time tau_0.