Analysis of radiative pion decayπ−→e−νγ

We give a quantitative account of radiative pion decays. By the chiral structure of the interaction and the fact of the low mass ratio between an electron and a pion, one can suppress the inner-bremsstrahlung contribution and correspondingly enhance the structure-dependent contribution by looking at decays with the emission of a negative-helicity electron. By this observation, we examine a way of determining the value of the structure-dependent parameter $\gamma$, giving particular attention to the decay spectra with this electron helicity. We also investigate the effects of a neutrino mass in this process.