Role of Strong Interactions in Decay Processes

An attack is made on the problem of determining which are the primary interactions that contribute to decay processes. It is necessary first to understand the rôle of the strong interactions in these processes; this has proven difficult in the past because of the appearance of infinities. It is shown that all infinities appearing in decay processes involving nucleons, pions, photons, and one lepton pair may be removed by renormalization to all orders in the strong and electromagnetic coupling constants. The necessary and sufficient condition for renormalizability is that the primary interactions that actually exist in nature form one of certain subclasses of a class of fourteen possible primary interactions. In particular, from this point of view it is incorrect to treat the $\pi$-meson decay as proceeding via Fermi interactions only. Two incidental results of this work are that the use of perturbation theory in computing the contribution of the pion decay interaction to $\mu$-meson absorption is justified, and that the "principle of minimal electromagnetic coupling" is violated in the radiative tensor decay of the $\pi$ meson.