Charge symmetry breaking of the nucleon-nucleon interaction:   $\rho$-$\omega$ mixing VERSUS nucleon mass splitting
  We investigate three models for the charge symmetry breaking (CSB) of the nucleon-nucleon ($NN$) interaction (based upon $\rho$-$\omega$ mixing, nucleon mass splitting, and phenomenology) that all reproduce the empirical value for the CSB of the $^1S_0$ scattering length ($\Delta a_{CSB}$) accurately. We reveal that these models make very different predictions for CSB in $^3P_J$ waves and examine the impact of this on some observable quantities of $A\geq 3$ nuclear systems. It turns out that the $^3$H-$^3$He binding energy difference is essentially ruled by $\Delta a_{CSB}$ and not very sensitive to CSB from $P$ waves. However, the Coulomb displacement energies (which are the subject of the Nolen-Schiffer anomaly) receive about 50% of their CSB contribution from $NN$ partial waves beyond $^1S_0$. Consequently, the predictions by the various CSB models differ here substantially (10-20%). Unfortunately, the evaluation of the leading Coulomb contributions carry a large uncertainty such that no discrimination between the competing CSB models can presently be made. To decide the issue we suggest to look into nuclear few-body reactions that are sensitive to CSB of the nuclear force. 
R. Machleidt and H. M\"uther