Lepton-Proton Two-Photon Exchange in Chiral Perturbation Theory

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.

Comments: 16 pages, 5 figures. Text slightly revised, results the same. Accepted for publication by Phys.Rev.D