# 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.

## Quantum Discord and the Quantum Advantage

Thursday Dec 01, 2011
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Entanglement is a paradigmatic example of quantum correlations, a presumed reason for the superior performance of quantum computation and an obvious divider of states and processes into classical and quantum. In the last decade all these notions were challenged. Entanglement does not capture the totality of non-classical behavior. Quantum discord (in its different versions) is a more general measure of quantum correlations. It can be related to the advantage in some tasks like the extraction of work from a Szilrad heat engine using Maxwell's demons with various resources.

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## Chern-Simons Theory, Vassiliev- Kontsevich Invariant, and Spinfoam Quantum Gravity

Thursday Dec 01, 2011
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We construct the q-deformed spinfoam vertex amplitude using Chern-Simons theory on the boundary 3-sphere of the 4-simplex. The rigorous definition involves the construction of Vassiliev-Kontsevich invariant for trivalent knot graph. Under the semiclassical asymptotics, the q-deformed spinfoam amplitude reproduce Regge gravity with cosmological constant at nondegenerate critical configurations.

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## Black Holes from Within Loop Quantum Gravity

Wednesday Nov 30, 2011
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In general relativity, the fields on a black hole horizon are obtained from those in the bulk by pullback and restriction. In quantum gravity, it would be natural to obtain them in the same manner. This is not fully realized in the quantum theory of isolated horizons in loop quantum gravity, in which a Chern-Simons phase space on the horizon is quantized separately from the bulk. I will outline an approach in which the quantum horizon degrees of freedom are simply components of the quantized bulk degrees of freedom.

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## Relative Locality, Kappa-Poincaré and the Relativity Principle

Wednesday Nov 23, 2011
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I briefly introduce the recently introduced idea of relativity of locality, which is a
consequence of a non-flat geometry of momentum space. Momentum space
can acquire nontrivial geometrical properties due to quantum gravity effects.
I study the relation of this framework with noncommutative geometry, and the
Quantum Group approach to noncommutative spaces. In particular I'm interested
in kappa-Poincaré, which is a Quantum Group that, as shown by Freidel and Livine,
in the 1+1D case emerges as the symmetry of effective field theory coupled with

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## Towards Loop Quantum Supergravity and its Applications

Wednesday Nov 16, 2011
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This talk will deal with a new connection formulation for higher-dimensional (Super)gravity theories and its applications. We will start by reviewing the basic ideas of loop quantum gravity. Next, the derivation of the new connection formulation will be discussed and it will be shown that the quantization methods developed in the context of loop quantum gravity apply. We comment on applications of the framework, focusing on making contact with String theory.

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## Parity and the Immirzi Parameter in Lorentzian Spinfoams

Wednesday Nov 02, 2011
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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

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

Tuesday Nov 01, 2011
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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.

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## WKB Techniques for Wigner 3nj Symbols

Wednesday Oct 19, 2011
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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.

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## Loop Gravity as the Dynamics of Topological Defects

Wednesday Sep 21, 2011
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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.

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

Thursday Sep 08, 2011
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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.

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## RECENT PUBLIC LECTURE

### Robert Spekkens: The riddle of the quantum sphinx: quantum states and category mistakes

Speaker: Robert Spekkens