Universal Velocity Correlations in Disordered and

The response of weakly disordered metallic grains to Aharonov-Bohm ux suggests a rescaling in which statistical correlators become universal. We derive an exact expression for a correlator of level \velocities," and provide numerical evidence which suggests that the universality extends to a wider class of systems and generalizes to arbitrary perturbations providing a new characterization of quantum chaos. These results are applied to Fermi velocities of complex lattices.