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 BCFW recursion relations define Yang-Mills and gravity amplitudes in terms of lower-point amplitudes. I will discuss several connections between the internal consistency of this recursive definition and the allowed interactions of massless, higher-spin particles.
Although the observational evidence for cosmological inflation is growing, the physical mechanism behind it is still unknown. In part this is because inflation probably occurred at energy scales many orders of magnitude higher than that at man-made or astrophysical particle accelerators. So how can we learn about inflation? How does it constrain microphysical theory? One approach to answering these questions is primarily theoretical: attempting to embed inflation in fundamental theories of quantum gravity, such as string theory.
For a quantum system with a d-dimensional Hilbert space, a symmetric informationally complete measurement (SIC) can be thought of as a set of d^2 pure states all having the same overlap. Constructions of SICs for composite systems usually do not make use of the composite structure but treat the system as a whole. Indeed for some cases, one can prove that a SIC cannot have the symmetry that one naturally associates with the composite structure.
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.