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# 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.

## Finite regions, spherical entanglement, and quantum gravity

Jeudi nov 14, 2013
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An exciting frontier in physics is to understand the quantum nature of gravitation in finite regions of spacetime. Study of these regions from below'', that is, by studying the quantum geometry of finite regions emerging from loop gravity and spin networks has recently resulted in a new road to the quantization of volume and to evidence that there is a robust gap in the volume spectrum. In this talk I will complement these results with recent work on conformal field theories in a particular finite region, a spherical ball of space.

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## Matter matters in asymptotically safe quantum gravity

Jeudi nov 07, 2013

The Functional
Renormalisation Group technique has received great attention in recent times
proving itself as a powerful tool to describe the high energy behaviour of
gravitational interactions.

Its key ingredient is a nontrivial fixed point of the theory renormalization
group flow which controls the behavior of the coupling constants in the
ultraviolet regime and ensures that physical quantities are safe from
divergences. I will briefly review the main ingredients of the gravitational asymptotic

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## A causal set action

Jeudi oct 31, 2013
Speaker(s):

Causal set theory is discrete, fully covariant theory of quantum
gravity. The discrete framework makes it necessary to reformulate
continuum concepts. One of these concepts is that of a derivative operator. It is
possible to define a derivative operator in causal sets that in
the continuum limit agrees with the d'Alembertian for a scalar
field. This operator can be used to define a causal set action, which
enables Monte-Carlo simulations. In this seminar I will present this operator and action and then

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## Asymptotically safe matrix models

Jeudi oct 24, 2013
Speaker(s):

The functional renormalization group
is a tool in the systematic search for Euclidean QFTs that works with
very little input: All one needs to specify is a field content,
symmetries and a notion of locality. The functional renormalization
group then allows one to scan this theory space for bare actions for
which the path integral can be performed nonperturbatively. These
actions appear as fixed points (and relevant deformations) of the
renormalization group flow (so-called asymptotic safety). Such a

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## Constructing theories from duality: my response to John Wheeler

Jeudi oct 17, 2013

The
late physicist John Wheeler, was renowned for his Socratic method of conducting
physics discussions. "Why is general relativity the way it is? What makes
it special?" were reportedly questions one should expect in his
presence. There are different answers to these questions, each requiring a set
of assumptions - which Wheeler would likely question again - and each bringing
with it new insights into physics as a whole. This talk will put forward

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## Superselection Sectors in AdS/CFT - Joint Quantum Gravity and String Theory Seminar

Jeudi oct 10, 2013
Speaker(s):

relating the degrees of freedom in a D dimensional bulk gravity theory to a (D-1) dimensional theory living on the boundary. I will argue that in fact the boundary theory contains only a subset of the bulk observables. For each state of the boundary theory, there are multiple bulk states dual to it, which can be operationally distinguished by observers who fall across event horizons. Based on arXiv:1210.3590.

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## The World is Discrete

Jeudi sep 19, 2013
Speaker(s):

We argue that the
scale-free spectrum that is observed in the cosmic microwave background is the
result of a phase transition in the early universe.  The observed tilt of
the spectrum, which has been measured to be 0.04, is shown to be equal to the
anomalous scaling dimension of the correlation function.  The phase
transition replaces inflation as the mechanism that produces this spectrum. The tilt further indicates that there is a fundamental small length scale in

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## Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Jeudi sep 12, 2013
Speaker(s):

A defining feature of holographic dualities is that, along with the bulk equations of motion, boundary correlators at any given time t determine those of observables deep in the bulk. We argue that this property emerges from the bulk gravitational Gauss law together with bulk quantum entanglement as embodied in the Reeh-Schlieder theorem. Stringy bulk degrees of freedom are not required and play little role even when they exist. As an example we study a toy model whose matter sector is a free scalar field.

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## Strong Binary Pulsar Constraints on Lorentz Violation in Gravity

Jeudi aoû 22, 2013
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Binary pulsars are excellent laboratories to test the building blocks of Einstein's theory of General

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## Perturbative Amplitudes and Ultraviolet Behavior of Supergravity Theories

Jeudi juin 13, 2013
Speaker(s):

Recently powerful techniques have emerged for performing multi-loop computations of scattering amplitudes in quantum gravity and  supergravity.  These techniques include generalized unitarity and the double-copy property, related to color-kinematics duality in gauge theory.  Using these  techniques, the ultraviolet divergence structure of N=8 supergravity, and more recently pure N=4 supergravity, have been assessed, not only in four space-time dimensions but also in higher dimensions.

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