Velocity distributions and aging in a cooling granular gas

We use large-scale molecular dynamics simulations to study freely evolving granular gases with dimensionality d=2,3. The system dissipates kinetic energy (or cools) due to inelastic collisions between granular particles. The density and velocity fields are approximately homogeneous at early times, and the system is said to be in a homogeneous cooling state (HCS). However, fluctuations in the density and velocity fields grow, and the system evolves into an inhomogeneous cooling state (ICS). We study the nature of velocity distributions in both the HCS and ICS. We also investigate the aging property of the velocity autocorrelation function.