Self-diffusion in granular gases

The coefficient of self-diffusion for a homogeneously cooling granular gas changes significantly if the impact-velocity dependence of the restitution coefficient epsilon is taken into account. For the case of a constant epsil on the particles spread logarithmically slowly with time, whereas a velocit y-dependent coefficient yields a power law time dependence. The impact of t he difference in these time dependences on the properties of a freely cooli ng granular gas is discussed.