Charge dependence of the nucleon-nucleon interaction due to pion-mass difference

Abstract

We calculate the charge-dependent effects on the nucleon-nucleon scattering length due to the mass difference between charged and neutral pions. This is done within the framework of the field-theoretic Bonn nucleon-nucleon interaction model, which is based entirely on meson exchange. We find that the pion-mass difference can account for about 80% of the experimental discrepancy between the proton-proton (or neutron-neutron) and proton-neutron scattering lengths. This is the first consistent calculation of the pion-mass difference effects taking into account all important one- and two-boson-exchange contributions to the nuclear force.