# A dispersive approach to two-photon exchange in elastic electron-proton scattering

## TL;DR

This paper presents a dispersive method to accurately calculate two-photon exchange corrections in elastic electron-proton scattering, incorporating nucleon and Delta states, and compares results with recent experimental data.

## Contribution

It introduces a dispersive approach that avoids off-shell uncertainties and ensures correct high-energy behavior, improving the theoretical understanding of two-photon exchange effects.

## Key findings

- Dispersive calculations agree with experimental cross section ratios.
- Method reduces uncertainties compared to traditional loop diagram evaluations.
- Results align with polarization transfer measurements.

## Abstract

We examine the two-photon exchange corrections to elastic electron-proton scattering within a dispersive approach, including contributions from both Nucleon and Delta intermediate states. The dispersive analysis avoids off-shell uncertainties inherent in traditional approaches based on direct evaluation of loop diagrams, and guarantees the correct unitary behavior in the high energy limit. Using empirical information on the electromagnetic nucleon elastic and N-Delta transition form factors, we compute the two-photon exchange corrections both algebraically and numerically. Results are compared with recent measurements of e+p to e-p cross section ratios from the CLAS, VEPP-3 and OLYMPUS experiments, as well as with polarization transfer observables.