Ring Kinetic Theory for Granular Response Functions

The response functions for an isolated (cooling or thermostated) granular gas are described by kinetic theory [1]. The linear kinetic equation is obtained by a systematic expansion of the dimensionless BBGKY hierarchy scaled relative to the mean free time and mean free path [2]. At first order beyond Boltzmann the effects of ring (repeated) collisions and associated mode coupling are included. Qualitative differences from the Boltzmann approximation are described. \\[4pt] [1] ``Kinetic Theory of Response Functions for the Hard Sphere Granular Fluid,'' A. Baskaran, J. Dufty, and J. Brey, J. Stat. Mech. 12, p12002 (2007); ``Linear Response for Granular Fluids,'' J. Dufty, in Frontiers in Nonequilibrium Physics, Prog. of Theor. Phys. Supp., (to appear). \\[0pt] [2] ``Kinetic Theory and Hydrodynamics for a Low Density Granular Gas,'' J. Dufty in Challenges in Granular Physics, T. Halsey and A. Mehta, eds. (World Scientific, N. J. 2002).