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.
Geometric flows, especially the Ricci flow, have been used with considerable success in recent years to address the Poincare and Thurston conjectures for 3-manifolds. In this talk, I will briefly introduce these geometric flows, and describe how they appear in a completely different context in the physics of string theory. I will then outline how recently developed techniques in geometric flows could be used to address questions of importance in string theory.
Experiments have ruled out unit-strength scalar-mediated fifth forces on scales ranging from 0.1 mm to 10,000 AU. However, allowing the scalar to have a quartic self-interaction weakens these constraints considerably. This weakening is due to the "chameleon mechanism", which gives the scalar field an effective mass that depends on the local matter density. I will describe the chameleon mechanism and discuss experimental constraints on self-interacting scalar fields.