Contribution of two-boson exchange with Δ(1232) excitation to parity-violating elastic electron-proton scattering

We study the leading electroweak corrections in the precision measurement of the strange form factors. Specifically, we calculate the two-boson exchange (TBE), two-photon exchange (TPE) plus γZ exchange (γZE), and corrections with Δ(1232) excitation to the parity-violating asymmetry of the elastic electron-proton scattering. The interplay between nucleon and Δ contributions is found to depend strongly on the kinematics, as δ_Δ begins as negligible at backward angles but becomes very large and negative and dominant at forward angles, while δ_N always stays positive and decreases monotonically with increasing ε. The total TBE corrections to the extracted values of G_E^s+βG_M^s in recent experiments of HAPPEX and G0 are, depending on kinematics, found to be large and range between 13% and -75%, but are found to be small in the case of A4 experiments.