  We present an extensive numerical study of dynamical heterogeneities and
their influence on diffusion in an athermal mesoscopic model for actively
deformed amorphous solids. At low strain rates the stress dynamics are governed
by cooperative regions of plastic events. On the basis of scaling arguments as
well as an extensive numerical study of an athermal elasto-plastic model, we
show that there is a direct link between the self-diffusion coefficient and the
size of cooperative regions at low strain rates. Both depend strongly on rate
and on system size. A measure of the mean square displacement of passive
tracers in deformed amorphous media thus gives information about the
microscopic rheology, such as the geometry of the cooperative regions and their
scaling with strain rate and system size.
