# Two-photon exchange in elastic electron-proton scattering

## TL;DR

This paper reviews recent advances in understanding two-photon exchange effects in elastic electron-proton scattering, comparing experimental results and theoretical models to clarify their impact on scattering measurements.

## Contribution

It provides a comprehensive comparison of experimental data and theoretical calculations on two-photon exchange in electron-proton scattering, highlighting current understanding and future directions.

## Key findings

- Experimental results show discrepancies in e+p to e-p cross section ratios.
- Theoretical models offer varying predictions of two-photon exchange effects.
- Current data suggest two-photon exchange significantly influences scattering measurements.

## Abstract

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 the ratio of e+p to e-p elastic scattering cross sections, and of the theoretical calculations describing them. A summary of the current experimental situation is provided, along with an outlook for future experiments.