Heavy quark diffusion in strongly coupled N=4 Yang-Mills theory

We express the heavy quark diffusion coefficient as the temporal variation of a Wilson line along the Schwinger-Keldysh contour. This generalizes the classical formula for diffusion as a force-force correlator to a non-Abelian theory. We use this formula to compute the diffusion coefficient in strongly coupled N=4 Yang-Mills theory by studying the fluctuations of a string in AdS(5)xS(5). The string solution spans the full Kruskal plane and gives access to contour correlations. The diffusion coefficient is D=2/root lambda pi T and is therefore parametrically smaller than momentum diffusion, eta/(e+p)=1/4 pi T. The quark mass must be much greater than T root lambda in order to treat the quark as a heavy quasiparticle. The result is discussed in the context of the Relativistic Heavy Ion Collider (RHIC) experiments.