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.
The problem of the quantum backreaction in expanding spaces is an old, as yet unresolved, question. In this talk I will consider the one-loop backreaction of a massless scalar which couples to the Ricci scalar in an expanding space with constant deceleration. I will show that the infrared divergences, which generically plague the one loop stress energy, can be removed by matching onto an earlier radiation era. An insignificant backreaction occurs, unless the coupling to the Ricci scalar is negative. Similar results hold for the graviton backreaction.
Recent data from the PAMELA, Fermi/LAT and INTEGRAL/SPI experiments, among others, give evidence of excess electrons and positrons in the galaxy, which might be due to annihilation of dark matter. Models in which the dark matter transforms under a hidden nonabelian gauge symmetry can naturally account for the unusual features needed to fit these data. I will discuss generic features of such models, some of their distinctive consequences for cosmology, and new results for reconciling their predictions with the anomalous observations.