Charge dependence and charge asymmetry of nuclear forces in chiral quark cluster models

We discuss charge-dependent effects on nucleon–nucleon scattering lengths in chiral quark cluster models. We find that, as in meson-exchange models, the pion-mass splitting can account for about 60% of the experimental difference between proton–proton and proton–neutron scattering lengths. Adding QED–QCD interference effects both the charge independence and charge symmetry breaking are reasonably understood.