QCD sum rules: Isospin symmetry breakings in pion-nucleon couplings

We use the method of QCD sum rules in the presence of an external point field to investigate isospin symmetry breakings in pion-nucleon couplings. Possible manifestations of such isospin symmetry breakings are examined in the context of low-energy nucleon-nucleon scattering. We discuss numerical results in relation to both the existing data and other theoretical predictions. {copyright} {ital 1998} {ital The American Physical Society}