# Video Library

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.

## Particle decay in the de Sitter universe

Thursday Oct 28, 2010
Speaker(s):

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 $m_c$

Scientific Areas:

## Infrared sensitivity of unstable vacua

Thursday Oct 28, 2010
Speaker(s):

TBA

Scientific Areas:

## Singular gauges and dS invariance of the graviton vacuum

Wednesday Oct 27, 2010
Speaker(s):

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 ÃÂ¢ÃÂÃÂcosmologists gaugeÃÂ¢ÃÂÃÂ is in fact singular on global de Sitter space.

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## Inflationary Correlation Functions without Infrared Divergences

Wednesday Oct 27, 2010
Speaker(s):

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.

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## The Feynman Propagator and Correlation Functions in an Inflating Spacetime

Wednesday Oct 27, 2010
Speaker(s):

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.

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## The problems of quantum gravity: from high-energy scattering to black holes and cosmology

Wednesday Oct 27, 2010
Speaker(s):

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.

Scientific Areas:

## The problems of quantum gravity: from high-energy scattering to black holes and cosmology

Wednesday Oct 27, 2010
Speaker(s):

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.

Collection/Series:
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## Resumming late time divergences and comparing thermal vs dS

Wednesday Oct 27, 2010
Speaker(s):

I will argue that the dynamical renormalization group can be used to resum late time divergences appearing in loop computations in de Sitter. In the case of a scalar field with quartic interactions, the resummed propagator is the massive one. Standard mean field theory techniques can then be used to estimate the mass. This is analogous to the thermal field theory story but with some notable differences. We discuss whether a critical point can exist in dS where mean field methods fail.

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## IR divergence problem in single-field models of inflation

Wednesday Oct 27, 2010
Speaker(s):

We clarify the origin of IR divergence in single-field models of inflation and provide the correct way to calculate the observable fluctuations. First, we show the presence of gauge degrees of freedom in the frequently used gauges such as the comoving gauge and the flat gauge. These gauge degrees of freedom are responsible for the IR divergences that appear in loop corrections of primordial perturbations. We propose, in this talk, one simple but explicit example of gauge-invariant quantities.

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## New Horizons in Cosmology: The Trace Anomaly, Cosmological Horizon Modes and Dynamical Dark Energy

Wednesday Oct 27, 2010
Speaker(s):

General Relativity receives quantum corrections relevant at macroscopic distance scales and near event horizons. These arise from the conformal scalar degrees of freedom in the extended effective field theory of gravity generated by the trace anomaly of massless quantum fields in curved space.

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## Next Public Lecture

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Wednesday Apr 05, 2017

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