Le contenu de cette page n’est pas disponible en français. Veuillez nous en excuser.

# 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.

## Parity and the Immirzi Parameter in Lorentzian Spinfoams

Mercredi nov 02, 2011
Speaker(s):

The parity invariance of spinfoam gravity is an open question. Naively, parity
breaking should reside in the sign of the Immirzi parameter. I show that the
new Lorentzian vertex formula is in fact independent of this sign, suggesting
that the dynamics is parity-invariant. The situation with boundary states and
operators is more complicated. I discuss parity-related pieces of the
transition amplitude and graviton propagator in the large-spin 4-simplex
limit. Numerical results indicate patterns similar to those in the Euclidean

Collection/Series:
Scientific Areas:

## The Fluid/Gravity Correspondence, Quantum Anomalies and a Generalized Entropy Current

Mardi nov 01, 2011
Speaker(s):

The fluid/gravity correspondence relates hydrodynamic flows in D spacetime dimensions to black hole dynamics in D+1 dimensions. It is an extension of black hole thermodynamics, where charges are upgraded into local currents, and the Bekenstein-Hawking entropy - into a local entropy current. I will propose a definition for a generalized local current of Wald entropy relevant to higher-curvature gravity. As an example, I will consider 5d gravity with a U(1) gauge field and a gravitational Chern-Simons term.

Collection/Series:
Scientific Areas:

## WKB Techniques for Wigner 3nj Symbols

Mercredi oct 19, 2011
Speaker(s):

This talk focuses on an application of a WKB technique that is a generalization of the Born-Oppenheimer approximation to the Schwinger model of angular momentum. This work makes it possible to express the asymptotic limits of higher 3nj symbols in terms of the asymptotic limits of lower 3nj symbols, when only a subset of quantum numbers are taken to be large. After an introduction of the the technique, we show that the 15j symbol has different asymptotic limits in terms of a combination of several Ponzano Regge actions when different subsets of quantum numbers are taken large.

Collection/Series:
Scientific Areas:

## Loop Gravity as the Dynamics of Topological Defects

Mercredi sep 21, 2011
Speaker(s):

A charged particle can detect the presence of a magnetic field confined into a solenoid. The strength of the effect depends only on the phase shift experienced by the particle's wave function, as dictated by the Wilson loop of the Maxwell connection around the solenoid. In this seminar I'll show that Loop Gravity has a structure analogous to the one relevant in the Aharonov-Bohm effect described above: it is a quantum theory of connections with curvature vanishing everywhere, except on a 1d network of topological defects.

Collection/Series:
Scientific Areas:

## Cosmology Meets Quantum Gravity: a Chiral Signature in the CMB?

Jeudi sep 08, 2011
Speaker(s):

Cosmology and quantum gravity have not always had the smoothest of interactions. As a case in point I'll summarize the calculation behind the prediction of tensor modes in inflationary universes and discuss the difficulties found in recasting this calculation in terms of Ashtekar-Barbero-Immirzi variables. Contrary to the belief that inflation is shielded from quantum gravity'', novelties are found, leading to the interesting prediction of a chiral signature in the gravitational wave background, proportional to the imaginary part of the Immirzi parameter.

Collection/Series:
Scientific Areas:

## Spin Systems as Toy Models for Emergent Gravity

Mercredi aoû 03, 2011

A number of recent proposals for a quantum theory of gravity are based on the idea that spacetime geometry and gravity are derivative concepts and only apply at an approximate level. Two fundamental challenges to any such approach are, at the conceptual level, the role of time in the emergent context and, technically, the fact that the lack of a fundamental spacetime makes difficult the straightforward application of well-known methods of statistical physics and quantum field theory to the problem.

Collection/Series:
Scientific Areas:

## Spinfoam Fermions

Mercredi juil 06, 2011
Speaker(s):

A serious shortcoming of spinfoam loop gravity is the absence of matter.
I present a minimal and surprisingly simple coupling of a chiral fermion field in the framework of spinfoam quantum gravity.
This result resonates with similar ones in early canonical loop theory: the naive fermion hamiltonian was found to be just the extension of the simple

Collection/Series:
Scientific Areas:

## The emergent gravity challenge: a few lessons from analogue gravity

Mercredi mai 04, 2011
Speaker(s):

Emergent gravity scenarios have become increasingly popular in recent times. In this talk I will review some evidence in this sense and discuss some lessons from toy models based on condensed matter analogues of gravity. These lessons suggest some (possibly) general features of the emergent gravity framework which not only can be tested with current astrophysical observations but can also improve our understanding of cosmological puzzles such as the dark energy one.

Collection/Series:
Scientific Areas:

## Counting horizon entropy in causal set quantum gravity

Jeudi avr 28, 2011
Speaker(s):
Collection/Series:
Scientific Areas:

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

Mercredi 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:

## RECENT PUBLIC LECTURE

### Quantum Mechanics and Spacetime in the 21st Century

Speaker: Nima Arkani-Hamed