The Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear   matter
  The quark-meson coupling model which we have developed previously is extended to incorporate the $\delta$ meson. It is then used to study the Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter. We find that, in combination with the {\it u-d\/} mass difference, the difference between quark scalar densities in protons and neutrons generates an effective neutron-proton mass difference of the right magnitude. Finally we find that isospin symmetry breaking in the quark condensates can be directly related to the $\delta$ meson field. 
K. Saito and A. W. Thomas