Model independence of the logarithmic lepton-mass singularities in the radiative corrections to Ml 3± decay

We have calculated the logarithmic lepton-mass singularities of the radiative corrections to order α to the three-body semileptonic decay of pseudoscalar mesons. No approximations concerning the smallness of the four-momentum transfer or the inner bremsstrahlung have been made. We find that the coefficients of the logarithmic lepton-mass singularities are structure independent. This result extends the validity of a theorem initially established by Marciano and Sirlin for the two-body semileptonic decay of pions and later proved to be valid for the semileptonic decay of baryons.