2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/158340Thanks 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.4 pages, 5 figures, talk given at 43nd Rencontres de Moriond on QCD and High-Energy Interactions, La Thuile, March 2007High Energy Physics - Phenomenologytext