Effects of weak disorder on strongly interacting electron systems

We discuss how the effects of a weak random potential are renormalized by strong interactions, assuming that the self-energy depends weakly on momentum and neglecting spin-orbit scattering. We find that if the effective mass is very large compared to Fs0(Fa0), ordinary (magnetic) impurities scatter close to the unitary limit. We discuss possible applications of these results to the heavy fermion compounds and the high temperature superconductors.