Charge asymmetry for electron (positron)-proton elastic scattering at large angles

Charge asymmetry in electron (positron) scattering arises from the interference of the Born amplitude and the box-type amplitude corresponding to two virtual photons exchange. It can be extracted from electron-proton and positron-proton scattering experiments, in the same kinematical conditions. Considering the virtual photon Compton scattering tensor, which contributes to the box-type amplitude, we separate proton and inelastic contributions in the intermediate state and parametrize the proton form factors as the sum of long-distance and short-distance interaction terms. Arguments based on analyticity are given in favor of cancellation of contributions from proton strong-interaction form factors and of inelastic intermediate states in the box-type amplitudes. In the framework of this model, with a realistic expression for nucleon form factors, numerical estimations are given for moderately high energies.