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 start with a brief qualitative discussion of the construction of a dS-invariant state for interacting theories using Euclidean methods and its real-time evolution within the closed-time-path formalism, as well as of the closely related in-in formalism. Next, I will focus on the two-point quantum correlation function for the Riemann tensor of the metric perturbations around dS including the one-loop correction from matter fields. A key object is the stress tensor two-point function, from which the one-loop Ricci correlator follows straightforwardly.
I will present the latest results from the searches for gravitational waves from the coalescence of binary systems of neutron stars and black holes in LIGO and Virgo data. We present results on data from the Fifth Science Run LIGO run S5 from Nov 2005 to Oct 2007, which was joint with Virgo's first Science Run VSR1 from May to Oct 2007. We also show how these methods are being applied in the current LIGO S6/ Virgo VSR2 data-taking run started in July 2009, and recently ended in October 2010.
We study the relation between two sets of correlators in interacting quantum field theory on de Sitter space. The first are correlators computed using in-in perturbation theory in the region of de Sitter space to the future of a cosmological horizon (also known as the expanding cosmological patch, the conformal patch, or the Poincare patch), and for which the free propagators are taken to be those of the free Euclidean vacuum. The second are correlators obtained by analytic continuation from interacting QFT on Euclidean de Sitter; i.e., they are correlators in the Hartle-Hawking vacuum.
We study particle decay in the de Sitter spacetime as given by first
order perturbation theory in an interacting quantum field theory.
We discuss first a general construction of bosonic two-point functions,
including a recently discovered class of tachyonic theories that do
exist in the de Sitter spacetime at discrete negative values of the squared mass parameter and have no Minkowskian counterpart.
We show then that for fields with masses above a critical mass $m_c$
there is no such thing as particle stability, so that decays forbidden
TBA
There has been a long-running discussion as to whether free gravitons on dS have a dS-invariant state. On the one hand, de Sitter invariant states are clearly singular in gauges favored by cosmologists; e.g. transverse traceless synchronous gauge associated with the k=0 slicing of dS. However, Higuchi has constructed a dS-invariant state using a different gauge. We resolve this tension by showing that the above ÃÂ¢ÃÂÃÂcosmologists gaugeÃÂ¢ÃÂÃÂ is in fact singular on global de Sitter space.
The definition of correlation functions relies on measuring distances on some late surface of equal energy density. If invariant distances are used, the curvature correlation functions of single-field inflation are free of any IR sensitivity. By contrast, conventional correlation functions, defined using the coordinate distance between pairs of points, receive large IR corrections if measured in a "large box" and if inflation lastet for a sufficiently long period.
We discuss the definition of the Feynman propagator in de Sitter space. We show that the ambiguities in the propagator zero-mode can be used to make sense of the behavior of low-momentum modes in an inflating space-time. We use this tool to calculate loop corrections to non-Gaussian correlation functions, and show that there are limits where the loop terms dominate. These models can be probed with the Planck satellite.
Much work on quantum gravity has focussed on short-distance problems such as non-renormalizability and singularities. However, quantization of gravity raises important long-distance issues, which may be more important guides to the conceptual advances required. These include the problems of black hole information and gauge invariant observables, and those of inflationary cosmology. An overview of aspects of these problems, and apparent connections, will be given.
Much work on quantum gravity has focused on short-distance problems such as non-renormalizability and singularities. However, quantization of gravity raises important long-distance issues, which may be more important guides to the conceptual advances required. These include the problems of black hole information and gauge invariant observables, and those of inflationary cosmology. An overview of aspects of these problems, and apparent connections, will be given.
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