New calculations of charge-symmetry breaking in the $\mathrm{NN}$ interaction lead to radically altered predictions for the difference between $\mathrm{nn}$ and $\mathrm{pp}$ scattering lengths. Inclusion of the ${\eta }^{\prime }$ meson and use of realistic magnetic couplings for the vector meson changes the sign as well as the magnitude of earlier results. This sensitivity arises in part from cancellations within the pseudoscalar and vector contributions separately, making precise calculations difficult. Meson mixing is determined from quark mass differences, and the finite width of the $\rho$ meson is included.

• Received 21 May 1979

DOI:https://doi.org/10.1103/PhysRevLett.43.1559