QED-QCD mixing effect and isospin violation in 1S0 NN scattering

The charge dependence of the nucleon-nucleon scattering length due to the quark effects are examined in a quark cluster model. In addition to the effects induced by the up-down quark mass difference and quark-exchange Coulomb interaction, we consider the interference effects of QCD and QED suggested by Maltman, Stephenson, and Goldman. We find that the total contribution of the quark effects to app − ann is large and in the direction indicated by the experiments. The effect is, however, small for app − anp.