Density dependence of charge symmetry breaking

We study the density dependence of charge symmetry breaking by calculating the energy difference as a function of density between adding one neutron or one proton to uniform nuclear matter. Isospin violation from electromagnetic interactions are expected to increase with density as the average distance between quarks decreases. In contrast, isospin violation from the up-down quark mass difference should decrease with density as the contributions from the small quark masses are suppressed by the increasing Fermi momentum. The Okamoto-Nolen-Schiffer (ONS) anomaly in the binding energy of mirror nuclei was studied at high density by adding a single neutron or a proton to a quark-gluon plasma. In the limit of very high density we find an anomaly equal to two-thirds of the Coulomb exchange energy of a proton. This effect is dominated by quark electromagnetic interactions - rather than by the up-down quark mass difference, and has the same sign as that observed in normal nuclei.