2011LPTHE, Paris
We consider domain-wall and $AdS$-black hole backgrounds in Lovelock theories of gravity. We construct a "c-function" $\mathcal N(r)$ for these, which we argue counts the number of effective fields at a given scale - on $AdS$ spaces it is related to the Euler anomaly, and at a black hole horizon it is proportional to the entropy. The monotonicity properties of $\mathcal N$ are controlled by the "gravitational field" which has opposite signs in the domain-wall and black hole backgrounds, due to the presence of negative (positive) energy in the former (latter). We show how $\mathcal N$ can be written as the ratio of the Wald entropy to a quantity resembling an effective phase space volume.
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CPT, Marseille
Loop Quantum Gravity has much developed in last few years. I review the present state of the theory, focusing on the following issues: the precise definition of the covariant theory, the relation with the old canonical LQG (and the separability of the Hilbert space), the finiteness of the transition amplitudes, the classical limit and the computation of the n-point functions, and the distinction between the theorems proved and the open hopes.
Zakopane lectures on loop gravity
LPT-ENS, Paris
I discuss the problem of localizing gravity on an anti-de-Sitter brane in string theory. This will lead to the study of a new class of holographic AdS4/CFT3 dualities, and is also related to the question of whether the graviton can acquire an arbitrarily-small mass in AdS spacetime.
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Perimeter Institute for Theoretical Physics, Waterloo
We have a proposal (based on an extension of M-theory) for passing through cosmological singularities. Our claim is that generically there is a short phase of antigravity: a drastic idea but one which very surprisingly seems to make sense.
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Imperial College, London
Control over symmetries at the quantum level plays a critical rôle in analysing the ultraviolet problem both in gauge theories and in theories of gravity. Recent dramatic cancellations of potentially divergent contributions to maximal supergravity have brought about a reevaluation of the applicable nonrenormalisation theorems, where both local gauge invariances and continuous global duality symmetries play key rôles. At the current point in time, these considerations suffice to explain all the surprising supergravity ultraviolet cancellations, and they also now agree with conclusions about divergence onset from string theory. However, more key tests at yet higher loop orders are anticipated. The results will shed important light on relations between supergravity, super Yang-Mills theory and superstring theory.
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University of California, Irvine
I will discuss how the nonperturbative treatment of pure gravity based on the Euclidean lattice formulation in four dimensions has so far supported the existence of a non-trivial ultaviolet fixed point, similar to what happens in other perturbatively non-renormalizable theories such as the non-linear sigma model. The appearance of such a fixed point implies a new non-trivial vacuum state, described among others by a gravitational condensate and a genuinely nonperturbative correlation length. In analogy to non-abelian gauge theories, which also have a non-trivial vacuum, the latter is expected to be related to the vacuum curvature condensate by simple dimensional (scaling) arguments, and thus plays the role of a scaling violation parameter. In more general terms, the appearance of a new vacuum state for gravitation leads to strong infrared divergences, which will manifest themselves for ex. as a running of Newton's $G$ over very large, cosmological distance scales. Towards the end of my talk I will discuss briefly the formal development of a manifestly covariant treatment for the running of $G$, and show how such small, but calculable, effects could perhaps be detected in future high precision cosmological observations.
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CPhT, Ecole polytechnique
I will discuss the algebraic proof of the existence of $\mathfrak e_7$ current Ward identities in the formal perturbative expansion of $\mathcal N=8$ supergravity based on 1007.5472. Some more attention will be devoted to the issue of compatibility of the $E_7$ invariant renormalisation prescription with supersymmetry. Electromagnetic duality in the presence of higher order local corrections will also be described through explicit examples.
Articles: E7(7) symmetry in perturbatively quantised N=8 supergravity and Counterterms vs. Dualities
Niels Bohr Institute
I will (try to) motivate a lattice study of quantum gravity, and how it fits into the framework of asymptotic safety, and for the particular lattice version we are using, CDT, into the framework of Horava-Lifshitz gravity. I will describe why the lattice theory is truly "entropic", and what numerical simulations can tell us about a "quantum universe".
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Washington University and IAP
General relativity has been well-tested in the weak-field slow-motion regime of the solar system. In binary pulsar systems, some tests of strong-field aspects of the theory have been carried out. In the future, testing GR in the strong-field, highly dynamical regime will be an important theme in experimental relativity. We describe a number of possible tests that could be carried out, including tests using astrophysical phenomena around black holes, tests using gravitational waves, and tests of black hole no-hair theorems using high-precision observations of stars orbiting our galactic center black hole.
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University of Utrecht
Horaire exceptionel 14h45
The near-horizon BPS geometries in five space-time dimensions are analyzed with the aim of determining the entropy and charges of supersymmetric black holes and black rings in the presence of higher-derivative couplings. Various subtleties will be explained and the results will be compared to corresponding results of microstate counting.
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CERN
We discuss a possible scenario of non-Wilsonian UV-completion of certain class of non-renormalizable theories, such as, theories that include graviton or Nambu-Goldstone-type derivatively-coupled scalars. In this approach theory self-completes itself by becoming classical in deep UV. We discuss implications of this phenomenon for graviton mass and for Higgsless unitarization of scattering of longitudinal W-bosons.
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Harvard
Horaire exceptionel 14h45
Article From Navier-Stokes To Einstein
University of Massachusetts Amherst & IHÉS
Robinson and Wilczek popularized the study of how gravity modifies the running of the gauge coupling constants. This subject has since then had a controversial history. The issues are illuminating, illustrating some of the distinctive features of effective field theory. In the end, I will argue against the whole enterprise.
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Princeton University
The talk will review recent theorems on the rigidity and stability of black holes, and will describe some recent results on the formation of black holes.
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Université de Mayence
Functional Renormalization Group Equations constitute a powerful tool to encode the perturbative and non-perturbative properties of a physical system. We present an algorithm to systematically compute the expansion of such flow equations in a given background quantity specified by the approximation scheme. The method is based on the intricate interplay between projection operators acting on the fields of the theory and off-diagonal heat-kernel techniques. The algorithm is purely algebraic and can be implemented on a computer algebra system, opening access to complex computations in, e.g., Gravity or Yang-Mills theory. As a first application of our projector method the heat-kernel coefficients for transverse vectors and transverse-traceless symmetric matrices are computed to second order in the curvature. In addition we re-derive the gravitational $\beta$-functions of the Einstein-Hilbert truncation, demonstrating their background-independence.
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Université de Rome
Horaire exceptionel 14h45
Precise navigation of deep space probes would be impossible without general relativity. In turn, precise orbit determination of planetary spacecraft, enabled by accurate measurements of angles, distances and velocities, has provided many tests of Einstein's theory. The seminar outlines the main results attained so far and the expectations from future, more challenging planetary missions. We review also recent findings in the claimed violations of laws of gravity, such as the Pioneer anomaly and the acceleration of deep space probes during Earth flybys.
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