Two-Photon Exchange in Electron-Proton Scattering

An investigation is made of the two-photon exchange contribution to $e-p$ scattering. The contribution is calculated in second Born approximation using potentials representing the charge and magnetic moment distributions of the proton. A fit to proton Compton scattering data is made and used to calculate the resonance contribution to $e-p$ scattering. At high energies, the resonant and nonresonant contributions to the two-photon exchange effect tend to cancel one another.