# 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.

## Renormalization in Noncommutative Quantum Field Theory

Thursday May 08, 2008
Speaker(s):

This talk presents some recent results in renormalizable noncommutative quantum field theory. After introducing the renormalization group approach in the commutative setting I will procede to its generalization to the simplest noncommutative model, $phi_4^{star 4}$ on the Moyal space. The well known phenomenon of ultraviolet/infrared mixing is cured by adding a harmonic potential term to the free action. Under the new renormalization group, adapted to the noncommutative geometry, this model turns out to be renormalizable to all orders in perturbation theory.

Collection/Series:
Scientific Areas:

## Trans-Planckian physics and renormalization

Thursday Apr 24, 2008

We analyze the trans-Planckian problem and its formulation in the context of cosmology, black-hole physics, and analogue models of gravity. In particular, we discuss the phenomenological approach to the trans-Planckian problem based on modified, locally Lorentz-breaking, dispersion relations (MDR). The main question is whether MDR leave an detectable imprint on macroscopic physics. In the framework of the semi-classical theory of gravity, this question can be unambiguously answered only through a rigorous formulation of quantum field theory on curved space with MDR.

Collection/Series:
Scientific Areas:

## Emergent Time in Barbour and Bertotti\'s Timeless Mechanics

Thursday Apr 10, 2008
Speaker(s):

The problem of time is studied in a toy model for quantum gravity: Barbour and Bertotti\'s timeless formulation of non-relativistic mechanics. We quantize this timeless theory using path integrals and compare it to the path integral quantization of parameterized Newtonian mechanics, which contains absolute time. In general, we find that the solutions to the timeless theory are energy eigenstates, as predicted by the usual canonical quantization.

Collection/Series:
Scientific Areas:

## Quantum Spacetime

Thursday Feb 14, 2008
Speaker(s):

The principles of Quantum Mechanics and of Classical General Relativity imply Uncertainty Relations between the different spacetime coordinates of the events, which yield to a basic model of Quantum Minkowski Space, having the full (classical) Poincare\' group as group of symmetries.

Collection/Series:
Scientific Areas:

## Loop Quantum Gravity and Deformation Quantization

Thursday Feb 07, 2008
Speaker(s):

Loop Quantum Gravity and Deformation Quantization

Collection/Series:
Scientific Areas:

## Braid-like Chiral States in Quantum gravity

Thursday Jan 31, 2008
Speaker(s):

There has been a dream that matter and gravity can be unified in a fundamental theory of quantum gravity. One of the main philosophies to realize this dream is that matter may be emergent degrees of freedom of a quantum theory of gravity. We study the propagation and interactions of braid-like chiral states in models of quantum gravity in which the states are (framed) four-valent spin networks embedded in a topological three manifold and the evolution moves are given by the dual Pachner moves. There are results for both the framed and unframed case.

Collection/Series:
Scientific Areas:

## Emergent gravity from noncommutative gauge theory

Thursday Jan 24, 2008
Speaker(s):

We show that the matrix-model for noncommutative U(n) gauge theory actually describes SU(n) gauge theory coupled to gravity.
The nonabelian gauge fields as well as additional scalar fields couple to a dynamical metric G_ab, which is given in terms of a Poisson structure. This leads to a gravity theory which is naturally related to noncommutativity, encoding those degrees of freedom which are usually interpreted as U(1) gauge fields. Essential features such as gravitational waves and the Newtonian limit are reproduced correctly.

Collection/Series:
Scientific Areas:

## Asymptotic safety

Thursday Nov 29, 2007
Speaker(s):

TBA

Collection/Series:
Scientific Areas:

## Automorphisms in Loop Quantum Gravity

Thursday Nov 15, 2007
Speaker(s):

There is a deep relation between Loop Quantum Gravity and notions from category theory, which have been pointed out by many researchers, such as Baez or Velhinho. Concepts like holonomies, connections and gauge transformations can be naturally formulated in that language. In this formulation, the (spatial) diffeomorphisms appear as the path grouopid automorphisms. We investigate the effect of extending the diffeomorphisms to all such automorphisms, which can be viewed as \"distributional diffeomorphisms\".

Collection/Series:
Scientific Areas:

## 3d quantum gravity and deformed special relativity

Thursday Sep 20, 2007
Speaker(s):

In 3d quantum gravity, Planck's constant, the Planck length and the cosmological constant control the lack of (co)-commutativity of quantities like angular momenta, momenta and postion coordinates. I will explain this statement, using the quantum groups which arise in the 3d quantum gravity but avoiding technical details. The non-commutative structures in 3d quantum gravity are quite different from those in the deformed version of special relativity desribed by the kappa-Poincare group, but can be related to the latter by an operation called semi-dualisation.

Collection/Series:
Scientific Areas: