Driven granular fluids

Dense granular media can be prepared in a stationary state by suitable driving. Such driving can be given by a random, momentum-conserving external force acting upon, say, a fluid comprised of inelastic hard spheres. While this out-of-equilibrium stationary state violates time reversal symmetry, it can still be investigated by means similar to ordinary fluids. For high enough density, the driven granular fluid undergoes a glass transition, and for this transition an extension to the mode-coupling theory can be derived. In addition to the quiescent stationary state, a kinetic theory as well as experiments in 2D for the active microrheology can be devised, where a selected intruder is pulled through the system as a probe for either constant velocity or force.