Determination of two-photon exchange amplitudes from elastic electron-proton scattering data

Using the available cross-section and polarization data for elastic electron-proton scattering, we provide an extraction of the two-photon exchange amplitudes at a common value of four-momentum transfer, around Q ² = 2.5 GeV^2. This analysis also predicts the e ⁺ p/e ^- p elastic-scattering cross-section ratio, which will be measured by forthcoming experiments.