We calculate the cross section for the lepton-proton bremsstrahlung process l+p→l′+p+γ in effective field theory. This process corresponds to an undetected background signal for the proposed MUSE experiment at PSI. MUSE is designed to measure elastic scattering of low-energy electrons and muons off a proton target in order to extract a precise value for the proton's r.m.s. radius. We show that the commonly used {\it peaking approximation}, which is used to evaluate the {\it radiative tail} for the elastic cross section, is not applicable for muon proton scattering at the low-energy MUSE kinematics. We also correct a misprint in a commonly cited review article.
@article{arxiv.1712.09963,
title = {Low-Energy Effective Field Theory of Lepton-Proton Bremsstrahlung},
author = {P. Talukdar and F. Myhrer and U. Raha},
journal= {arXiv preprint arXiv:1712.09963},
year = {2023}
}