Randomly driven granular fluids: Collisional statistics and short scale structure

We present a molecular-dynamics and kinetic theory study of granular material, modeled by inelastic hard disks, fluidized by a random driving force. The focus is on collisional averages and short-distance correlations in the nonequilibrium steady state, in order to analyze in a quantitative manner the breakdown of molecular chaos, i.e., factorization of the two-particle distribution function, f((2))(x(1), x(2))similar or equal tochif((1))(x(1))f((1))(x(2)) in a product of single-particle ones, where x(i)={r(i), v(i)} with i = 1,2 and chi represents the position correlation. We have found that molecular chaos is only violated in a small region of the two-particle phase space {x(1), x(2)}, where there is a predominance of grazing collisions. The size of this singular region grows with increasing inelasticity. The existence of particle- and noise-induced recollisions magnifies the departure from mean-field behavior. The implications of this breakdown in several physical quantities are explored.