We calculate the two-boson-exchange (TBE) corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a parton model using the formalism of generalized parton distributions (GPD's). We find that these effects can reach a few percent and are comparable in size with the current experimental measurements of strange-quark effects in the proton neutral weak current. Our result is also compared with the result of the hadronic model.
Hard Photon Correction to e+e- -> + - and Effects of Neutral Weak Current