# 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.

## Semiclassical approaches to IR issues in quasi de Sitter universes

Friday Oct 29, 2010
Speaker(s):

Using simple semiclassical relations it is possible to show that the conventional cosmological correlation functions are affected by significant IR corrections in quasi de Sitter space-times when averaged over very large volumes (in the "large box"). The IR effects apparently imply a breakdown of perturbation theory in the large box on sufficiently long time scales, for example the time between self-reproduction and reheating in chaotic inflation. An interpretation of the apparent breakdown of the perturbative expansion of gravity will also be briefly discussed.

Scientific Areas:

## Gravity-Driven Cosmology

Friday Oct 29, 2010
Speaker(s):

A simple phenomenological model for early cosmological evolution is constructed. Its motivation is the physics of quantum infrared effects in a de Sitter geometry.

Scientific Areas:

## Interacting Quantum Fields in de Sitter Space

Friday Oct 29, 2010
Speaker(s):

Infrared logarithms are factors of the logarithm of the inflationary scale factor which arise in quantum field theoretic loop corrections that involve either massless, minimally coupled scalars or gravitons. They have been found by myself and collaborators in 1PI functions and by Steven Weinberg in the power spectrum of primordial perturbations. Because the inflationary scale factor grows so rapidly, infrared logarithms enhance loop corrections far beyond expectations based upon the coupling constant.

Scientific Areas:

## On radiation and IR divergences in dS space

Thursday Oct 28, 2010
Speaker(s):

It is well known that there should be a total cancellation of the IR
divergences in closed systems described by interacting quantum field
theories, such as QED and gravity. I am going to show that such a
cancellation does not happen in de Sitter space.

Scientific Areas:

## Infrared instability of massless scalars in De Sitter space-time.

Thursday Oct 28, 2010
Speaker(s):

Vacuum expectation value of the square of the quantum field operator of massless or light scalar field is calculated in the De Sitter space-time. The suggested method of calculation is different from the standard one used in the 80th. The calculations are heavily based on the De Sitter covarinace of the relevant quantities. The found result is significanlty

Scientific Areas:

## Ultraviolet Complete Quantum Gravity

Thursday Oct 28, 2010
Speaker(s):

An ultraviolet complete quantum gravity theory is formulated in which vertex functions in Feynman graphs are entire functions and the propagating graviton is described by a local, causal propagator. A scalar-tensor action describes classical gravity theory. The cosmological constant problem is investigated in the context of the ultraviolet complete quantum gravity. Also investigated are black holes and cosmology.

Collection/Series:
Scientific Areas:

## One-loop Riemann correlators and dS invariance

Thursday Oct 28, 2010
Speaker(s):

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.

Scientific Areas:

## Searches for coalescence of binary systems in LIGO and Virgo data

Thursday Oct 28, 2010
Speaker(s):

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.

Collection/Series:

## On the Equivalence between Euclidean and In-In Formalisms in de Sitter QFT

Thursday Oct 28, 2010
Speaker(s):

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.

Scientific Areas:

## 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:

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