Kinetics of inhomogeneous cooling in granular fluids.

We study the dynamical behavior of a freely evolving granular gas, where the particles undergo inelastic collisions. The velocity and density fields exhibit complex pattern dynamics, which is reminiscent of phase ordering systems. For example, in the initial time regime, the density field stays (approximately) uniform, and the system is said to be in a homogeneous cooling state (HCS). At later times, the density field undergoes nonlinear clustering, and the system continues to lose energy in an inhomogeneous cooling state (ICS). We quantitatively characterize the HCS-->ICS crossover as a function of system parameters. Furthermore, we study nonlinear growth processes in the ICS by invoking analogies from studies of phase ordering dynamics.