Lepton-Flavour Violation in Ordinary and Supersymmetric Grand Unified Theories

Abstract

By an explicit calculation we show that in ordinary SU(5) logarithmic divergence in the amplitude of μ → eγ cancels among diagrams and remaining finite part is suppressed by at least 1/M_GUT². In SUSY SU(5), when the effect of flavour changing wave function renormalization is taken into account such logarithmic correction disappears, provided a condition is met among SUSY breaking masses. In SUGRA-inspired SUSY GUT the remaining logarithmic effect is argued not to be taken as a prediction of the theory.