Lepton-Proton Two-Photon Exchange in Chiral Perturbation Theory

TL;DR

This paper calculates two-photon exchange corrections in low-energy elastic lepton-proton scattering using heavy baryon chiral perturbation theory, including lepton mass effects, and finds results consistent with existing soft photon approximation models.

Contribution

It provides a next-to-leading order chiral perturbation theory calculation of two-photon exchange corrections with non-zero lepton mass, advancing theoretical precision.

Findings

Infrared singularity-free two-photon exchange contribution matches existing models.

Calculation includes lepton mass effects at next-to-leading order.

Results are in good numerical agreement with standard soft photon approximation predictions.

Abstract

We use heavy baryon chiral perturbation theory to evaluate the two-photon exchange corrections to the low-energy elastic lepton-proton scattering at next-to-leading order accuracy, i.e., ${\mathcal O}(\alpha, M^{-1})$, including a non-zero lepton mass. We consider the elastic proton intermediate state in the two-photon exchange together in the soft photon approximation. The infrared singular contributions are projected out using dimensional regularization. The resulting infrared singularity-free two-photon exchange contribution is in good numerical agreement with existing predictions based on standard diagrammatic soft photon approximation evaluations.