Two-photon exchange in elastic electron-proton scattering : QCD factorization approach

TL;DR

This paper estimates the two-photon exchange contribution to elastic electron-proton scattering at high momentum transfer using QCD factorization, showing it behaves as 1/Q^4 and can be expressed via nucleon distribution amplitudes.

Contribution

It introduces a model-independent way to express the two-photon exchange amplitude in terms of leading twist nucleon distribution amplitudes at large Q^2.

Findings

Two-photon exchange amplitude scales as 1/Q^4.

Expressed in terms of leading twist nucleon distribution amplitudes.

Provides estimates consistent with existing and upcoming experimental data.

Abstract

We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer $Q^2$. It is shown that the leading two-photon exchange amplitude behaves as $1/Q^4$ relative to the one-photon amplitude, and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.