Helicity amplitudes in massless QED to higher orders in the dimensional regulator

Abstract: We analytically calculate one- and two-loop helicity amplitudes in massless QED, by adopting a four-dimensional tensor decomposition. We draw our attention to four-fermion and Compton scattering processes to higher orders in the dimensional regulator, as required for theoretical predictions at N$^3$LO. We organise loop amplitudes by proposing an efficient algorithm at integrand level to group Feynman graphs into integral families. We study the singular structure of these amplitudes and discuss the correspondence between QED and QCD processes. We present our results in terms of generalised polylogarithms up to transcendental weight six.