Universal scaling dynamics in a perturbed granular gas

We study the response of a granular system at rest to an instantaneous input of energy in a localised region. We present scaling arguments that show that, in d dimensions, the radius of the resulting disturbance increases with time t as t α , and the energy decreases as t -α d , where the exponent α=1/( d +1) is independent of the coefficient of restitution. We support our arguments with an exact calculation in one dimension and event-driven molecular-dynamics simulations of hard-sphere particles in two and three dimensions.