Analysis of radiative pion decay. pi. /sup -/. -->. e/sup -/. nu gamma

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 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.