Séminaires sur les aspects théoriques et expérimentaux de la gravitation
 2012 | ||
| 13 décembre 2012 | Sergey Solodukhin Université de Tours | Entanglement entropy of black holes In this talk I will review the notion of entanglement entropy and its applications, in particular, to the problem of the black hole entropy. Transparents de l'exposé pdf |
| 23 novembre 2012 | Thibault Damour IHES horaire exceptionel 14h45 | Poincaré et la théorie de la relativité We shall review the contributions of Henri Poincaré to the Theory of Relativity. These contributions were both conceptual and technical. We shall also discuss why these contributions have not been fully appreciated at the time. Transparents de l'exposé pdf |
| 15 novembre 2012 | Francis Bernardeau IPhT CEA-Saclay | The growth of gravitational instabilities in an expanding universe The large-scale structure of the universe is thought to have emerged out of primordial metric fluctuations that have been amplified by gravitational instabilities throughout the cosmic expansion. However a self gravitating pressure-less fluid in an expanding background forms a complicated system for which, beyond the regime where the density and velocity perturbations are small, little is known. On the other hand being able to decipher the large-scale structure of the universe would bring a wealth of information on its matter and energy content and is therefore of crucial importance in the context of the coming surveys. In this talk I will present some historical perspectives on the approaches that have been used and then present how perturbation theory techniques can give insights into the growth of structure and into the physics of a self gravitating fluid in general. Latest results that these approaches have brought, in particular from resummation techniques, will be presented and commented. Transparents de l'exposé PDF |
| 8 novembre 2012 | Riccardo Sturani Urbino | Effective field theory methods in the post-Newtonian framework for the
2-body problem in General Relativity The Effective Field Theory approach can be employed to derive the conservative and dissipative dynamics of a gravitationally bound binary system. It will be shown how the post-Newtonian (PN) approximation to General Relativity can be neatly accommodated in a field theoretical framework, and how the standard tools developed for quantum field theory (as for instance the Feynman path integral and the renormalization group flow) can be helpful in treating the classical 2-body problem in General Relativity. As an application, it will be shown how the 3PN Hamiltonian has been reproduced via an algorithm implemented in Mathematica and the progress towards the computation of the 4PN Hamiltonian will be presented. Transparents de l'exposé PDF |
| 18 octobre 2012 | Norbert Straumann University of Zürich | On the Einstein-Grossmann collaboration 100 years ago On the basis of his 'Zurich Notebook' I shall describe a particularly fruitful phase in Einstein's struggle on the way to general relativity. These research notes are an extremely illuminating source for understanding Einstein's main physical arguments and conceptual difficulties that delayed his discovery of general relativity by about three years. Together with the `Entwurf' theory in collaboration with Marcel Grossmann, these notes also show that the final theory was missed late in 1912 within a hair's breadth. The Einstein-Grossmann theory, published almost exactly hundred years ago, contains, however, virtually all essential elements of Einstein's definite gravitation theory. Transparents de l'exposé PDF |
| 18 octobre 2012 | Jakob Palmkvist IHES horaire exceptionel 14h45 - Centre de conférence Simons | Borcherds algebras and supergravity Gauge deformations of maximal supergravity in $D=11-n$ dimensions generically give rise to a tensor hierarchy of p-form fields that transform in specific representations of the global symmetry group $E_n$. I will show how the formulas defining the hierarchy can be derived from a Borcherds superalgebra, which is an infinite-dimensional extension of the Lie algebra of $E_n$. For various dimensions D, all such Borcherds superalgebras can be embedded into a single one, which may play a role similar to those of the related Kac-Moody algebras $E_{10}$ and $E_{11}$ as possible underlying symmetries of M-theory. The talk is based on my papers 1110.4892 and 1203.5107 (hep-th), and on work in progress together with Axel Kleinschmidt, Jesper Greitz and Paul Howe. Transparents de l'exposé PDF |
| 4 octobre 2012 | Pascal Chardonnet Université de Savoie/LAPTH Annecy-le-Vieux | What are Gamma-Ray Bursts? Gamma-Ray Bursts (GRBs) are flashes of high-energy light. They emit as much as energy as our Sun will release in its entire lifetime. The quest to understand astrophysical origin of gamma-ray bursts represents one of the most important inquiries in astrophysics. GRBs are also becoming a unique tool to study both astrophysics and cosmology in helping us to understand the universe. In this seminar I will review the observational properties of GRBs and I will present the current explanations of GRBs. Transparents de l'exposé PDF |
| 13 septembre 2012 | Maximo Banados P. Universidad Católica de Chile | The action for higher spin black holes in three dimensions It has been point out recently that the SL(N,R)xSL(N,R) Chern-Simons functional (in 3d) can be interpreted as an interacting action for higher spin gauge fields. This opens the door to many interesting question related to gravity coupled to higher spin fields. We show in this seminar how to evaluate the action of higher spin black hole backgrounds in the Euclidean sector, thus providing a definition for their free energy. Transparents de l'exposé PDF |
| 21 juin 2012 | Zvi Bern UCLA | Gravity as a double copy of gauge theory Recent developments showing that in a precise sense perturbative gravity can be viewed as a double copy of gauge theory. Implications for the UV properties of supergravity are discussed. Transparents de l'exposé PDF |
| 3 mai 2012 | Eric Bergshoeff Université de Groningen | Massive Higher-Derivative Gravity We discuss a general procedure of how to construct unitary higher-derivative gravity theories. As an example we apply this procedure to construct the 3D New Massive Gravity theory. We show how the same procedure can be used to construct a similar massive higher-derivative theory, be it so far only at the linearized level, in four dimensions. The connection with other massive gravity theories in the literature is discussed. Transparents de l'exposé PDF |
| 3 mai 2012 | Cédric Deffayet APC, Paris horaire exceptionel 14h45 | Some recent results on massive gravity Models of "massive gravity" are in part motivated by the wish to provide alternative explanations to the observed acceleration of the Universe by considering "Infra-Red" modifications to General Relativity (GR). The (unique) theory of a free massive graviton on flat space is known for a long time as the Pauli-Fierz theory. It is in particular plagued by the van Dam-Veltman-Zakharov discontinuity, which states that the Pauli-Fierz theory does not converge to linearized GR when one lets the mass of the graviton go to zero. A way out, relying on non linear completions of Pauli-Fierz theory, was however proposed by Vainshtein in the 70's. Such non linear completions introduce however generically new pathologies in the construction. I will introduce and discuss some recent efforts to better understand and cure the various problems encountered. Transparents de l'exposé PDF |
| 26 avril 2012 | Viatcheslav Mukhanov Université de Munich et Chaire Blaise Pascal horaire exceptionel 11h00 | Asymptotic freedom, confinement and triviality in classical $\lambda\, \phi^4$ theory I will consider classical $\lambda\, \phi^4$ theory in the presence of the external source and show that already in classical theory one can recover renormalization group structure in this theory. Moreover, I will show that in the case of negative lambda one has asymptotically free theory and prove the confinement in this theory. It also will be shown that for positive lambda the theory is trivial Transparents de l'exposé PDF |
| 29 mars 2012 | Mikhael Volkov Université de Tours | Hairy black holes and self-accelerated cosmologies in the bigravity theory We study homogeneous and isotropic cosmologies in the recently proposed massive gravity theory with two dynamical metrics that is maintained to be ghost-free. The graviton mass manifests itself either at late times by leading to a self-acceleration, or at early times by removing the initial singularity. In addition, we present solutions describing black holes surrounded by a cloud of massive graviton `hair'. Transparents de l'exposé PDF |
| 15 mars 2012 | Aristide Baratin AEI, Golm Annulé -- Cancelled | State sums, group field theory and (quantum) geometry State sum models are discrete versions of a functional integral, which show up as models for the quantum geometry of space-time in certain approaches to quantum gravity. They can also be viewed as the amplitudes of higher dimensional analogues of Feynman diagrams, generated by so-called 'group field theories'. I will first present results which bridge the gap between the `background free' language of state sums and the language of quantum field theory on a fixed background space-time. I will then present group field theories and show how they can serve as a tentative formulation of quantum gravity in four dimensions. |
| 9 février 2012 | François Beguin Université Paris-Sud et DMA, ENS Centre de conférence Simons | Dynamics of Bianchi spacetimes Bianchi spacetimes are defined to be spatially homogeneous spacetimes. About forty years ago, Belinski, Kalatnikov, Lifschitz, and Misner have proposed a rather complete description, based on heursitic arguments, of the behavior of Bianchi spacetimes close to their initial singularity. In particular, a "generic" Bianchi spacetimes is expected to exhibit a "chaotic" oscillatory behavior closed to its initial singularity. Unfortunately, up to very recently, essentially no result going in this direction had been proved rigorously. Some progress have been made in 2010 by Liebscher and al., Reiterer and Trubowitz, and myself. I will present these progress and try to sketch what can be hoped in a near future. Transparents de l'exposé PDF |
| 26 janvier 2012 | Axel Kleinschmidt AEI, Golm horaire exceptionel 14h45 | Infinite discrete symmetries near singularities and modular forms When approaching a spacelike singularity the BKL conjecture states that the classical relativity dynamics are governed by chaotic oscillations. These can be alternatively described using a so-called cosmological billiard. When quantising this system one is led to automorphic forms of hyperbolic Weyl groups. The construction of some of these automorphic forms can be phrased conveniently using division algebras. If time permits some features of other Eisenstein series will also be discussed. Transparents de l'exposé PDF |
| 26 janvier 2012 | Renaud Parentani LPT, Orsay | Analogue black hole radiation in Bose Einstein condensates The phonon spectrum in supersonic flows displays a rich phenomelogogy. Whereas some effects are quite similar to what was found for black holes, others are new because they are governed by dispersive effects. I shall focus on the so called black hole laser which occurs when the condensate crosses twice the speed of sound. In this situation, the phonon spectrum possesses a discrete set of complex frequency modes. Interestingly, this lasing effect can be conceived as a self-amplified Hawking radiation. Transparents de l'exposé PDF |