Two-photon exchange in elastic electron-pion scattering

TL;DR

This paper calculates the two-photon exchange amplitude in elastic electron-pion scattering, revealing the dominance of elastic contributions at low Q^2 and the significance of inelastic effects at higher Q^2, with implications for scattering amplitude behavior.

Contribution

It introduces a dispersion-relation inspired approach to include elastic and inelastic contributions, modeling inelastic effects with meson contributions, advancing understanding of scattering amplitudes.

Findings

Elastic contribution dominates at Q^2 < 2 GeV^2

Inelastic contribution becomes relevant at higher Q^2

Explains rapid growth of amplitude at backward angles

Abstract

We calculate two-photon exchange amplitude for the elastic electron-pion scattering in the dispersion-relation inspired approach, including both elastic and inelastic contributions. The latter was modelled as a sum of \rho and b_1(1235) meson contributions. We find that at Q^2 < 2 GeV^2 the elastic contribution is dominant, similarly to electron-proton scattering case. At higher Q^2 the inelastic contribution is not negligible, but still smaller than the elastic one. We also explain observed rapid amplitude growth at backward angles.