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.
I will describe the current state of our attempts to characterize the nature of the Dark Energy, the name given to the unknown phenomenology that is driving the observed accelerating cosmic expansion. There is a historical analogy between our current situation and the days of
We use a field theoretic generalization of the Wigner-Weisskopf method to study the stability of the Bunch-Davies vacuum state for a massless, conformally coupled interacting test field in de Sitter space. A simple example of the impact of vacuum decay upon a non-gaussian correlation is discussed. Single particle excitations also decay into two particle states, leading to particle production that hastens the exiting of modes from the de Sitter horizon resulting in the production of \emph{entangled superhorizon pairs} with a population consistent with unitary evolution.
I will give a new set of operational postulates from which quantum theory can be reconstructed. These are (1) Definiteness: There is a one-to-one correspondence between the set of pure states and the set of maximal effects such that we get probability one for a pure state followed the corresponding maximal effect. (2) Information locality: If we perform maximal measurements on the components of a composite system then we effect a maximal measurement on the composite. (3) Tomographic locality: The state of a composite system can be determined by making measurements on its components.
After reviewing the basics of Coleman deLuccia tunneling, especially in the thin-wall limit, I discuss an (almost) exact tunneling solution in a piecewise linear and quadratic potential. A comparison with the exact solution for a piecewise linear potential demonstrates the dependence of the tunneling rate on the exact shape of the potential.
Finally, I will mention applications when determining initial conditions for inflation in the landscape. Based on arXiv:1102.4742 [hep-th].
Neutrino oscillations has been observed and confirmed at two mass splittings (\Delta m^2), which is consistent with three generations of neutrinos and an unitary mixing matrix. Despite the rapid progress in understanding neutrino oscillations in the last decade, two large questions remain about neutrino oscillation parameters at \Delta m^2 ~ 0.001 eV^2. Is \theta_{23} exactly 45 degrees, indicating an additional symmetry in neutrino mixing? Is \theta_{13} non-zero, which would mean there could be CP violation in the neutrino sector.