The Okamoto-Nolen-Schiffer anomaly without p-ω mixing

Abstract

We examine the effect of isospin-violating meson-nucleon coupling constants and of π-η mixing on the binding-energy differences of mirror nuclei in a model that possesses no contribution from p- ω mixing. The 3He 3H binding-energy difference is computed in a nonrelativistic approach using a realistic wave function. We find the 3He 3H binding-energy difference very sensitive to the short-distance behavior of the nucleon-nucleon potential. We conclude that for the typically hard Bonn form factors such modles cannot account for the observed binding-energy difference in the three-nucleon system. For the medium-mass region ( A = 15–41) the binding-energy differences of mirror nuclei are computed using a relativistic mean-field approximation to the Walecka model. We obtain large binding-energy differences - of the order of several hundred KeV - arising from the pseudoscalar sector. Two effects are primarily responsible for this new finding: a) the inclusion of isospin breaking in the pion-nucleon coupling constant and b) the in-medium enhancement of the small components of the bound-state wave functions. We look for off-shell ambiguities in these results and find them to be large; while 70–85% of the anomaly can be explained with a pseudoscalar coupling only 30% of it can be accounted for with a pseudovector vertex.