Polarization phenomena in e∓N elastic scattering, for axial parametrization of two-photon exchange

Abstract We analyze polarization phenomena for elastic lepton–nucleon scattering, parametrizing the 2 γ -exchange contribution, as the product of lepton and nucleon axial vector currents, that correspond to C = + 1 exchange in the annihilation channel. We found two combinations of polarization observables (one for three T-odd observables and another one for five T-even observables, which allow to measure the ratio G E ( Q 2 ) / G M ( Q 2 ) of nucleon electromagnetic form factors in model-independent way, without any specific assumption about the 2 γ -exchange mechanism. Both these important combinations have a general character and do not depend on the choice of the spin structure for the 2 γ -exchange.