  Although the notion of mechanical noise is expected to play a key role in the
non-linear rheology of athermally sheared amorphous systems, its
characterization has so far remained elusive. Here, we show using molecular
dynamic simulations that in spite of the presence of strong spatio-temporal
correlations in the system, the local stress exhibits normal diffusion under
the effect of the mechanical noise in the finite driving regime. The diffusion
constant appears to be proportional to the mean plastic activity. Our data
suggests that the corresponding proportionality constant is density
independent, and can be directly related to the specific form of the
rheological flow curve, pointing the way to a generic way of modeling
mechanical noise in mean-field equations.
