Radiative Corrections to Pion-Nucleon Coupling Constants

We formulate a renormalization procedure for avoiding the problem of electromagnetic divergences in second-order electromagnetic amplitudes. We apply it to evaluate radiative corrections to pion-nucleon coupling constants. Such corrections are essentially divided into two categories: "low momentum" to ordinary minimal-coupling expressions and "tadpole" corrections originating from the high-momentum part of the photon integral. The first part is calculated using a Cottingham procedure, weak partial conservation of axial-vector current (PCAC), and saturation by low-lying intermediate states. The tadpole contribution is related to the analogous one in the case of electromagnetic mass shifts and is parametrized in terms of the ratio $\frac{C_3}{C_8}$ between tadpole-electromagnetic and medium-strong interactions and of the deviations from S${\mathrm{U}}_3$ symmetry for meson-baryon coupling constants. The corrections to the pion-nucleon coupling constants due to electromagnetic mass shifts are estimated separately.