Effects of non-standard couplings, radiative corrections and neutrino masses on the lepton spectra in μ and τ decays

Abstract We investigate the combined effect of neutrino masses and non-standard couplings on the various lepton spectra in μ and τ decays. We emphasize the energy spectra of the neutrinos, which can be measured by secondary reactions in the new KARMEN experiment and hence will yield novel information on deviations from the VA structure. To constrain these couplings, QED radiative corrections have to be taken into account. We evaluated them and found small corrections to the neutrino spectra.