Universal dephasing rate due to diluted Kondo impurities.

We calculate the dephasing rate due to magnetic impurities in a weakly disordered metal as measured in a weak-localization experiment. If the density nS of magnetic impurities is sufficiently low, the dephasing rate 1/tauphi is a universal function, 1/tauphi=(nS/nu)f(T/TK), where TK is the Kondo temperature and nu is the density of states. We show that inelastic vertex corrections with a typical energy transfer DeltaE are suppressed by powers of 1/(tauphiDeltaE) proportional to nS. Therefore, the dephasing rate can be calculated from the inelastic cross section proportional to pinu ImT-/pinuT/2, where T is the T matrix which is evaluated numerically exactly using the numerical renormalization group.