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.
We consider the spectral action as an action functional for modified gravity on a spacetime that exhibits a fractal structure modeled on an Apollonian packing of 3-spheres (packed swiss cheese) or on a fractal arrangements of dodecahedral spaces. The contributions in the asymptotic expansion of the spectral action, that arise from the real poles of the zeta function, include the Einstein-Hilbert action with cosmological term and conformal and Gauss-Bonnet gravity terms.
I will describe a proposal for a generalization of the BMS group in which the conformal isometries of the sphere (Lorentz group) are replaced by arbitrary sphere diffeomorphisms. I describe the computation of canonical charges and show that the associated Ward identities are equivalent to the Cachazo-Strominger subleading soft graviton formula. Based on joint work with Alok Laddha.