Cages and anomalous diffusion in vibrated dense granular media
Caging is the typical microscopic phenomenon that “traps” molecules in a liquid at low temperature. The usual Brownian Motion of a tracer experiences a temporary “dynamical arrest” which eventually is broken restoring normal diffusion. In this work we have shown that at intermediate densities and temperature the same phenomenon occurs in granular liquids. At large densities and lower temperatures the late normal diffusion is replaced with superdiffusion. Interpretation of this surprising phenomenon is related to the presence of an emerging collective inertia inducing coherent collective motion of the granular liquids which takes longer and longer times to relax.