Walsh, T. F.; Zerwas, P. Two-photon processes in the parton model. Physics Letters B. 1973, 44 (2): 195–198. doi:10.1016/0370-2693(73)90520-0(英语).
Witten, E. Anomalous cross section for photon-photon scattering in gauge theories. Nuclear Physics B. 1977, 120 (2): 189–202. doi:10.1016/0550-3213(77)90038-4(英语).