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A detailed study of two-photon exchange in unpolarized and polarized elastic electron--nucleon scattering is presented, taking particular account of nucleon finite size effects. Contributions from nucleon elastic intermediate states are found to have a strong angular dependence, which leads to a partial resolution of the discrepancy between the Rosenbluth and polarization transfer measurements of the proton electric to magnetic form factor ratio, G_E/G_M. The two-photon exchange contribution to the longitudinal polarization transfer P_L is small, whereas the contribution to the transverse polarization transfer P_T is enhanced at backward angles by several percent, increasing with Q^2. This gives rise to a small, ~3% suppression of G_E/G_M obtained from the polarization transfer ratio P_T/P_L at large Q^2. We also compare the two-photon exchange effects with data on the ratio of e^+ p to e^- p cross sections, which is predicted to be enhanced at backward angles. Finally, we evaluate the corrections to the form factors of the neutron, and estimate the elastic intermediate state contribution to the ^3He form factors.
Two-photon exchange contributions to elastic electron-proton scattering cross sections are evaluated in a simple hadronic model including the finite size of the proton. The corrections are found to be small in magnitude, but with a strong angular dep
We review recent theoretical and experimental progress on the role of two-photon exchange (TPE) in electron-proton scattering at low to moderate momentum transfers. We make a detailed comparison and analysis of the results of competing experiments on
We report new precision measurements of the elastic electron-proton scattering cross section for momentum transfer squared (Q$^2$) up to 15.75~gevsq. These data allow for improved extraction of the proton magnetic form factor at high Q$^2$ and nearly
One way to treat the infrared divergences of the electroweak Next-to-Leading-Order (NLO) differential cross sections to parity-violating (PV) electron-proton scattering is by adding soft-photon emission contribution. Although more physical, the resul
The two-photon-exchange (TPE) effect plays a key role to extract the form factors (FFs) of the proton. In this work, we present some exact properties on the TPE effect in the elastic $ep$ scattering based on four types of typical and general interact