Relaxation in yield stress systems through elastically interacting   activated events
  We study consequences of long-range elasticity in thermally assisted dynamics of yield stress materials. Within a two-dimensinal mesoscopic model we calculate the mean-square displacement and the dynamical structure factor for tracer particle trajectories. The ballistic regime at short time scales is associated with a compressed exponential decay in the dynamical structure factor, followed by a subdiffusive crossover prior to the onset of diffusion. We relate this crossover to spatiotemporal correlations and thus go beyond established mean field predictions. 
Ezequiel E. Ferrero and Kirsten Martens and Jean-Louis Barrat
cond-mat.soft cond-mat.dis-nn cond-mat.stat-mech