Charge effects in meson-nucleon coupling constants

Abstract

Several quark models of charge effects in meson-nucleon coupling constants are reviewed. The emission of a meson by the electromagnetic (e.m.) interaction is calculated in a nonrelativistic quark potential model. Existing inaccuracies and errors in the perturbative calculation of the charge-independent coupling constants and of effects of the u-d mass difference in this model are corrected. We find that both e.m. and quark-mass difference effects are small, being of the order of 0.1–0.3%, except for a charge-independence breaking contribution of −1.7% from the meson mass appearing in a boson normalization factor. The perturbative one-gluon-exchange contribution to the charge-independent coupling constant is found to account for only about 60% of the magnitude of empirical coupling constants, thus indicating a need for additional mechanisms for meson emission.