Parity-Violating Nucleon-Nucleon Force in the 1/Nc Expansion

Several experimental investigations have observed parity violation (PV) in nuclear systems-a consequence of the weak force between quarks. We apply the 1/N-c expansion of QCD to the P-violating T-conserving component of the nucleon-nucleon (NN) potential. We show there are two leading-order operators, both of which affect (p) over right arrowp scattering at order N-c. We find an additional four operators at order N(c)(0)sin(2)theta(w) and six at O(1/N-c). Pion exchange in the PV NN force is suppressed by 1/N-c and sin(2)theta(w), providing a quantitative explanation for its nonobservation up to this time. The large-N-c hierarchy of other PV NN force mechanisms is consistent with estimates of the couplings in phenomenological models. The PV observed in (p) over right arrowp scattering data is compatible with natural values for the strong and weak coupling constants: there is no evidence of tine-tuning.