Séminaires Cosmologie 2013-2014

  Mardi 1er juillet à 14h, salle 110

Jérôme Gleyzes (IphT CEA-Saclay) : Healthy theories beyond Horndeski

In search for a candidate that could explain the current acceleration of the Universe, a lot of attention has been given recently to Galileon theories, or in their generalized form, Horndeski theories. They are interesting as they represent the most general scalar tensor theories that do not lead to equations of motion containing more than two derivatives. This restriction is generally thought to be of great importance, as generically, higher order derivatives lead to ghost instabilities. I will present a new class of scalar tensor theories that are broader than Horndeski and, as such, do bring higher order derivatives. However, when studying carefully the theories, it was shown that they do not propagate any additional ghostly degree of freedom. I will give details on how and why this is possible, and I’ll further talk about the uncommon phenomenology associated. Indeed, these theories exhibit a new type of coupling to matter, even when the latter is minimally coupled.

  Mercredi 28 mai à 14h, salle 114

Martin Bucher (APC) : B modes from inflation : the current state of play

  Mercredi 19 février à 11h, salle 114

Germain Rousseaux (Laboratoire Pprime of Poitiers) : Interaction Houle-Courant : application à la Physique des trous noirs

La propagation d’ondes de gravité longues en eau peu profonde et en présence d’un courant est décrite par l’équation de Beltrami-Laplace dans une métrique de Painlevé-Gullstrand. Cette constatation est à l’origine de la constitution d’une communauté dite de "Gravitation Analogue" qui ambitionne de tester en laboratoire des prédictions issues de la Relativité Générale comme la radiation de Hawking des horizons de trous noirs inobservable en Astrophysique. Nous présenterons nos expériences de gravitation analogue en hydraulique. Nous décrirons notre espace-temps effectif en caractérisant la propagation des ondes en présence d’un contre-courant. Une étude de la relation de dispersion de la houle sera menée en fonction de la vitesse du contre-courant et de la hauteur d’eau. Nous insisterons sur l’existence des ondes à énergies négatives ainsi que la présence d’un mode zéro dans nos mesures.

  Mercredi 29 janvier à 11h, salle 110

Mikhail Volkov (Tours U) : Energy in massive gravity theories

  Vendredi 24 janvier à 14h, salle 110

Minas Tsoukalas : General scale invariance

We present the most general actions of a single scalar field and two scalarfields coupled to gravity, consistent with second order field equations in four dimensions, possessinglocal scale invariance. We apply two different methods to arrive at our results. One method, Riccigauging, was known to the literature and we find this to produce the same result for the case ofone scalar field as a more efficient method presented here. However, we also find our moreefficient method to be much more general when we consider two scalar fields. Locally scale invariantactions are also presented for theories with more than two scalar fields coupled to gravity andwe explain how one could construct the most general actions for any number of scalar fields.

  mercredi 10 décembre à 10h30, salle 110

Ted Jacobson (U. of Maryland) : The black hole information paradox and its resolution (without firewalls)

  mercredi 27 novembre à 14h, salle 110

Luigi PILO (Dept of Physical and Chemical Sciences, INFN associated group l’Aquila) : The Cosmological side of Massive Gravity

I review the status massive gravity. Besides purely theoretical consideration, the study of massive versions of general relativity is motivated as a model of dark energy. The navigation through the various models will be guided by two basic principles : reproducing small scale tests of gravity (solar system and bellow) and the existence of sensible cosmological solutions. Interestingly, there is as general construction of basically all massive gravity theories with five degrees of freedom or less based on Hamiltonian analysis. Surprising enough the class of favored models are not a nonlinear generalization of the Fierz-Pauli theory.

  mardi 19 novembre à 14h, salle 110

Yann Mambrini (LPT, Orsay) : Recent aspects of dark matter phenomenology

  mardi 1er octobre à 11h, salle 110

Paul Shellard (DAMTP, Cambridge) : Planck and Non-Gaussian Inflation

The Planck satellite crosses new precision thresholds in the study of the cosmic microwave sky, like COBE and WMAP before it. However, it has also crossed qualitative thresholds by opening up new windows on the Universe, including the quantitative exploration of non-Gaussian statistics and gravitational lensing. This talk will overview the importance of non-Gaussianity for identifying fingerprints of new physics in both the late and early universe, before discussing the results of non-Gaussian searches using the Planck data.