Isospin symmetry breakings as from QCD sum rules

Abstract

We investigate isospin symmetry breakings, especially those connected with pion-nucleon couplings and the neutron-proton mass difference, by making use of the method of QCD sum rules in the presence of an external pion field. Manifestations of such isospin symmetry breakings are examined briefly in relation to low-energy nucleon-nucleon 1 S 0 scatterings. We discuss the prospect of understanding the various isospin symmetry breaking phenomena observed in low-energy nuclear physics by extending chiral perturbation theory ( χPT) to include isospin symmetry breakings (ISB). We emphasize that QCD sum rules help to establish χPT/ISB out of QCD by eliminating an excessive number of ISB condensate parameters, making χPT/ISB a worthy extension of χPT.