Isospin-violating meson-nucleon vertices as an alternate mechanism of charge-symmetry breaking

We compute isospin-violating meson-nucleon coupling constants and their consequent charge-symmetry-breaking (CSB) nucleon-nucleon potentials. The couplings result from evaluating matrix elements of quark currents between nucleon states in a nonrelativistic constituent quark model; the isospin violations arise from the difference in the up and down constituent quark masses. We find, in particular, that isospin violation in the omega-meson–nucleon vertex dominates the class IV CSB potential obtained from these considerations. We evaluate the resulting spin-singlet–triplet mixing angles, the quantities germane to the difference of neutron and proton analyzing powers measured in elastic n→-p→ scattering, and find them commensurate to those computed originally using the on-shell value of the ρ-ω mixing amplitude. The use of the on-shell ρ-ω mixing amplitude at ${\mathit{q}}^2$=0 has been called into question; rather, the amplitude is zero in a wide class of models. Our model possesses no contribution from ρ-ω mixing at ${\mathit{q}}^2$=0, and we find that omega-meson exchange suffices to explain the measured n-p analyzing power difference at 183 MeV. © 1996 The American Physical Society.