Ring kinetic theory for an idealized granular gas

The dynamics of inelastic hard spheres is described in terms of the binary collision expansion, yielding the corresponding pseudo-Liouville equation and BBGKY hierarchy for the reduced distribution functions. Based on cluster expansion techniques we derive the Boltzmann and ring kinetic equations for inelastic hard spheres. In the simple ring approximation, we calculate the structure factor S (k,t) of vorticity fluctuations in a freely evolving, dilute granular gas. The kinetic theory result agrees with the result derived previously from fluctuating hydrodynamics. If the fluctuations in the flow field can be considered incompressible, S (k,t) determines the spatial correlations in the flow velocities, which are of dynamic origin and exhibit long range r−d-behavior. The analytic results are compared with molecular dynamics simulations.