Radiative corrections to pion decays

A calculation is made of the effect of the hadronic structure of the pion on the radiative corrections to the branching ratio π → eν/π → μν. The correction due to the axial weak current is calculated by constructing a phenomenological Lagrangian for the π, A1, and rho mesons with minimally broken chiral symmetry and by using field-current identities. The phenomenological Lagrangian contains 5 free parameters which are determined by the pion decay rate, the rho and A1 masses, and the decay rates rho → e+e- and rho → 2π. It is first used to calculate the pion charge radius, the axial form factor for π → eνγ, and the rates A1 → rhoπ (longitudinal and transverse); then the axial correction to π → eν/π → μν is calculated to be 3 x 10-4. The correction to the branching ratio due to the vector weak current is calculated using the π0 → 2γ decay rate and the assumption that the process occurs through a quark triangle diagram, yielding a value which is dependent on the log of the cut-off (quark mass) and is estimated to be 5 x 10-4. (Diss. Abstr. Int., B)