Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
Large mixing angles and a mild mass hierarchy are observed in neutrino oscillations, in stark contrast with the quarks and charged leptons sectors where very hierarchical masses come along with small mixings.
We review and discuss the neutrino mass patterns that are technically natural, in the context of the seesaw mechanism and with a quark-lepton unification perspective.