The Two-Boson-Exchange Correction to Parity-Violating Elastic Electron-Proton Scattering

We calculate the two-boson-exchange (TBE) corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the nucleon and the $\Delta(1232)$ intermediate states. We find that $\Delta$ contribution $\delta_\Delta$ is, in general, comparable with the nucleon contribution $\delta_N$ and the current experimental measurements of strange-quark effects in the proton neutral weak current. The total TBE corrections to the current extracted values of $G^{s}_{E}+\beta G^{s}_{M}$ in recent experiments are found to lie in the range of $-7\sim +7%$.