Bifurcations of an inelastic hard disk system with a heat bath under weak gravity

Molecular dynamics simulations on a two-dimensional inelastic hard disk system under gravity with a heat bath were performed. In a weakly excited state (the condensed phase), the relationship between the non-Gaussian velocity probability distribution function or the flatness and the packing fraction was discussed. We also found that the spatial velocity correlation function takes positive values for all position in the condensed phase, but becomes negative at the half of the system when the system is highly excited.