  An impact of particles' roughness on the self-diffusion coefficient in
granular gases is investigated. For a simplified collision model where the
normal and tangential restitution coefficients are assumed to be constant we
develop an analytical theory for the diffusion coefficient, which takes into
account non-Maxwellain form of the velocity-angular velocity distribution
function. We perform molecular dynamics simulations for a gas in a homogeneous
cooling state and study the dependence of the self-diffusion coefficient on
restitution coefficients. Our theoretical results are in a good agreement with
the simulation data.
