# Quantum Gravity

This series consists of talks in the area of Quantum Gravity.

## Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

## The Klein Gordon field as a wave function: causality and localization

Wednesday Mar 02, 2011
Speaker(s):

Usually in quantum field theory one considers two different interpretations:
1: The field is an infinite number of quantum oscillators, giving rise to a wave functional \Psi(\phi).
2: The positive frequency component of a field, \phi_+(x), is a wave function analogous to standard quantum mechanics.
While interpretation 2 is often only mentioned implicitly it is crucial to standard computations of measurable scattering probabilities.

Collection/Series:
Scientific Areas:

## Spin Foams and Noncommutative Geometry

Wednesday Feb 23, 2011
Speaker(s):

We extend the formalism of embedded spin networks and spin foams to include topological data that encode the underlying three-manifold or
four-manifold as a branched cover. These data are expressed as
monodromies, in a way similar to the encoding of the gravitational field
via holonomies. We then describe convolution algebras of spin networks and
spin foams, based on the different ways in which the same topology can be
realized as a branched covering via covering moves, and on possible

Collection/Series:
Scientific Areas:

## Aspects of confinement from the functional Renormalization Group

Wednesday Dec 01, 2010
Speaker(s):

The functional Renormalization Group is a continuum method to study quantum field theories in the non-perturbative regime. In Yang-Mills theory, it can be used to relate fully nonperturbative low-order correlation functions in particular gauges to observables such as confinement order parameters. As a special application, we determine the order of the phase transition and the critical temperature for various gauge groups (SU(N), N=3,.,12, Sp(2) and E(7)). This also allows to investigate what determines the order of the deconfinement phase transition.

Collection/Series:
Scientific Areas:

## Is temperature the speed of time? Thermal time and the Tolman effect

Tuesday Nov 16, 2010
Speaker(s):

Why is a vertical column of gas at thermal equilibrium slighly hotter at the bottom than a the top? My answer in this talk will be that time runs slower in a deeper gravitational potential, and temperature is nothing but the (inverse) speed of time. Specifically, I will (i) introduce Rovelli's notion of thermal time, (ii) use it to provide a "principle" characterization of thermal equilibrium in stationary spacetimes, and (iii) effortlessly derive the Tolman-Ehrenfest relation.

Collection/Series:
Scientific Areas:

## Quantum polyhedra in loop quantum gravity

Tuesday Nov 09, 2010
Speaker(s):

Interwiners describe quanta of space in loop quantum gravity. In this talk I show that the Hilbert space of SU(2) intertwiners has as semiclassical limit the phase space of a classical system originally considered by Minkowski: convex polyhedra with N facets of given areas and normals. This result sharpens Penrose spin-geometry theorem. The knowledge of the classical system associated to intertwiner space can be fruitfully used: I show that many properties of the spectrum of the volume operator can be derived via Bohr-Sommerfeld quantization of the volume of a classical polyhedron.

Collection/Series:
Scientific Areas:

## U(N) framework and simplicity constraints for spin foam models

Wednesday Nov 03, 2010
Speaker(s):

In the context of loop quantum gravity and spin foam models, the simplicity constraints are essential in that they allow to write general relativity as a constrained topological theory.
I will first recall the spin foam quantization procedure and focus more particularly on the step consisting in implementing the simplicity constraints.

Collection/Series:
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:

## A New Perspective on Quantum Field Theory

Wednesday Oct 20, 2010
Speaker(s):

The Exact Renormalization Group (ERG) is a technique which can be fruitfully applied to systems with local interactions that exhibit a large number of degrees of freedom per correlation length. In the first part of the talk I will give a very general overview of the ERG, focussing on its applications in quantum field theory (QFT) and critical phenomena. In the second part I will discuss how a particular extension of the formalism suggests a new understanding of correlation functions in QFTs, in general, and gauge theories in particular.

Collection/Series:
Scientific Areas:

## Proposal for Divergence-Free Quantization of Covariant Scalar Fields

Wednesday Oct 06, 2010
Speaker(s):

Guided by idealized but soluble nonrenormalizable models, a nontraditional proposal for the quantization of covariant scalar field theories is advanced, which achieves a term-by-term, divergence-free perturbation analysis of interacting models expanded about a suitable pseudofree theory [differing from a free theory by an $O(\hbar^2)$ term].

Collection/Series:
Scientific Areas:

## An apology for DRS

Wednesday Sep 22, 2010

In my talk I would like to discuss the present status of Doubly Special Relativity. DSR is an extension of Special Relativity aimed at describing kinematics of particles and fields in the regime where (quantum) gravity effects might become relevant. I will discuss an interplay between DSR physics and mathematics of Hopf algebras.

Collection/Series:
Scientific Areas:

## RECENT PUBLIC LECTURE

### Amanda Peet, University of Toronto and Perimeter Institute

Speaker: Amanda Peet