Helicity amplitudes in light-cone and Feynman-diagram gauges Junmou Chen, Kaoru Hagiwara, Junichi Kanzaki, Kentarou Mawatari and Ya-Juan Zheng Eur. Phys. J. Plus, 139 4 (2024) 332 Published online: 15 April 2024 DOI: 10.1140/epjp/s13360-024-05067-5