  The influence of an applied shear field on the dynamics of an aging colloidal
suspension has been investigated by the dynamic light scattering determination
of the density autocorrelation function. Though a stationary state is never
observed, the slow dynamics crosses between two different non-equilibrium
regimes as soon as the structural relaxation time approaches the inverse shear
rate. In the shear dominated regime (at high shear rate values) the structural
relaxation time is found to be strongly sensitive to shear rate while aging
proceeds at a very slow rate. The effect of shear on the detailed shape of the
density autocorrelation function is quantitatively described assuming that the
structural relaxation process arises from the heterogeneous superposition of
many relaxing units each one independently coupled to shear with a parallel
composition rule for timescales.
