Multi-Photon Amplitudes for Next-to-Leading Order QCD
Vittorio Del Duca, William B. Kilgore, Fabio Maltoni
TL;DR
This paper provides compact six-parton tree-level amplitudes involving up to three photons and detailed five-parton one-loop expansions, enabling complete NLO QCD calculations for processes with photons in the final state. It develops a color-ordered, helicity-based framework and a photon insertion method to derive photon-inclusive amplitudes from gluon-dominated QCD results, while addressing subtleties in external versus internal photon couplings at one loop. The primary contributions include explicit MHV-based expressions for multi-photon tree amplitudes and comprehensive one-loop decompositions into primitive amplitudes, together with cross-section formulas. These results are essential for accurate NLO (and NNLO) predictions of photon-rich backgrounds and signals in Higgs-related and related processes at the LHC, as well as for photon-associated jet production in other collider settings.
Abstract
We present the tree-level amplitudes involving one, two and three photons that are required for next-to-leading order QCD calculations of production rates of three final-state particles. We also present the required one-loop amplitudes in terms of previously published results.