Thanks to the absence of tree order, the six-photon processes is a good laboratory to study multi-leg one-loop diagrams. Particularly, there are enough on-shell external legs to observe a special Landau singularity: the double parton scattering.
Cite
@article{arxiv.0804.1315,
title = {The six-photon amplitude},
author = {C. Bernicot},
journal= {arXiv preprint arXiv:0804.1315},
year = {2008}
}
Comments
4 pages, 5 figures, talk given at 43nd Rencontres de Moriond on QCD and High-Energy Interactions, La Thuile, March 2007