Radiative Tail in $\pi_{e2}$ Decay and Some Comments on $\mu-e$ Universality

摘要

The result of lowest-order perturbation theory calculations of the photon andpositron spectra in radiative pion(e2) decay are generalized to all orders ofperturbation theory using the structure-function method. An additional sourceof radiative corrections to the ratio of the positron and muon channels of piondecay, due to emission of virtual and real photons and pairs, is considered. Itdepends on details of the detection of the final particles and is large enoughto be taken into account in theoretical estimates with a level of accuracy of0.1%.