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Théorie

Superluminality of Matter in the Multicritical Universe

Orateur: 
Petr Horava (Berkeley U.)
Lieu: 
454A - Valentin/Klee
Horaire: 
Friday, 30. March 2012 - 14:00

First I will review the ideas and concepts of quantum gravity with
anisotropic scaling, which has attracted a lot of attention in
recent years both because of its improved ultraviolet behavior
and for its applications ranging from holographic renormalization,
to the causal dynamical triangulations approach to quantum gravity,
to the mathematics of the Ricci flow on Riemannian manifolds.
Then I will present the "multicritical universe" scenario,
in which gravity with anisotropic scaling is minimally coupled to

Probing Dark Matter with Neutrinos

Orateur: 
Ina Sarcevic (Arizona U.)
Lieu: 
366A - Klimt (3rd floor)
Horaire: 
Tuesday, 20. March 2012 - 14:00

 Dark Matter particles can be captured in the core of the Sun or the Earth,
or in the Galactic center, by interacting with the nuclei in the medium. The
capture rate depends on the composition of the medium, dark matter mass
and its local density. If the captured dark matter annihilate or decay into
the Standard Model particles, there is a possibility of producing neutrinos
which can be detected via muon tracks or showers. I will present theoretical
predictions for the indirect detection of the dark matter particles via neutrino

Anatomy of bispectra in general single-field inflation -- modal expansions

Orateur: 
Thorsten Battefeld (U. of Goettingen)
Lieu: 
366A - Klimt (UNUSUAL ROOM)
Horaire: 
Tuesday, 13. March 2012 - 14:00

I discuss methods to disentangle complex, non-seperable bispectra into least correlated basic shape constituents; for subsequent data comparison and reconstruction of primordial shapes, modal expansions are used. As a concrete case study, I focus on bispectra of single-field inflationary models described by general Lorentz invariant Lagrangians that are at most first order in field derivatives (including fast-roll models) and identify which templates provide good approximations. The scaling of relative contributions to the total bispectrum is computed as slow roll is relaxed.

Problem of Time in Quantum Gravity

Orateur: 
Edward Anderson (APC)
Lieu: 
454A - Valentin
Horaire: 
Tuesday, 6. March 2012 - 14:00

This concerns how what one means by "time" in GR is not the same as what one means by "time" in QM, causing foundational difficulties in trying to combine these two individually successful theoretical arenas.  I will cover the multiple facets of this problem, and some of the strategies suggested to resolve it (which have a long history of none working when examined in detail, ergo this probably remains an open problem).  A variety of toy models usually suffice to illustrate the various points in question in a somewhat more technically tractable setting than ful

Gravitational Waves and Kaluza-Klein Modes from Cosmic Super-Strings

Orateur: 
Dufaux Jean-François (APC)
Lieu: 
646A - Mondrian
Horaire: 
Tuesday, 28. February 2012 - 14:00

Cosmic super-strings are fundamental objects of string theory that have a cosmological size and evolve as a network of cosmic strings. They could lead to observational signatures of string theory, notably through gravitational wave (GW) astronomy, if they can be distinguished to some degree from their field theory counterparts. In the first part of this talk, I will revisit the computation of the GW background produced by cosmic (super-)string networks and discuss its essential and distinctive properties.

The mass distribution of dark matter halos

Orateur: 
Ixandra Achitouv (LUTH, Meudon)
Lieu: 
454A - Klee/Valentin
Horaire: 
Tuesday, 21. February 2012 - 14:00

Dark Matter halos are the building blocks of the cosmic structure
formation. The halo mass function quantifies their number density as
function of the mass and it is a key quantity to predicting several
large scale structure observables. In this talk, I will review the
latest theoretical advancements on the derivation of a halo mass
function which encodes physical aspects of the halo formation process
and is capable of reproducing numerical N-body simulation results with
unprecedented accuracy.

Soutenance de thèse : Multi-trace deformations in AdS/CFT models of cosmological singularities and condensed matter

Orateur: 
Lorenzo Battarra (APC)
Lieu: 
454A - Valentin
Horaire: 
Monday, 13. February 2012 - 14:00
The AdS/CFT correspondence provides a framework in which intrinsically quantum gravitational phenomena can be investigated in terms of a non–gravitational field theory. In a different regime, it allows an alternative description of certain strongly coupled field theo- ries via the properties of classical solutions of supergravity.

The light-cone averaging and the luminosity-redshift relation

Orateur: 
Giovanni Marozzi (College de France)
Lieu: 
454A - Klee/Valentin
Horaire: 
Tuesday, 14. February 2012 - 14:00

I will show a general gauge invariant formalism for defining
cosmological averages that are relevant for observations based on
light-like signals. Such averages involve either null hypersurfaces
corresponding to a family of past light-cones or compact surfaces
given by their intersection with timelike hypersurfaces. Afterwards,
using such formalism, together with adapted "geodesic light-cone"
coordinates, I will show as induced backreaction effect emerges from

Self tuning and the cosmological constant problem

Orateur: 
Christos Charmousis (LPT Orsay)
Home Institute: 
Unusual day, time and room!!
Lieu: 
483A - MALEVITCH
Horaire: 
Wednesday, 1. February 2012 - 13:30

We will discuss the cosmological constant problem in the context of
self-tuning scalar tensor theories in 4 dimensions. After reviewing the
most general scalar tensor theory proposed in the 70 's by Hornedski we
shall define and then apply the self-tuning filter and reduce to a scalar
tensor theory dubbed fab 4. We shall briefly discuss some of its geometric
and other properties.

Asymptotically (anti) de Sitter Black Holes and Wormholes with a Self Interacting Scalar Field in Four Dimensions.

Orateur: 
Andrés Anabalon
Home Institute: 
Adolfo Ibanez University, Valparaiso (Chile)
Lieu: 
454A - Klee
Horaire: 
Tuesday, 7. February 2012 - 14:00
The aim of the talk is to report on the existence of a wide variety of exact solutions, ranging from black holes to wormholes, when a conformally coupled scalar field with a self interacting potential containing a linear, a cubic and a quartic self interaction is taken as a source of the energy-momentum tensor, in the Einstein theory with a cosmological constant. Among all the solutions there are two particularly interesting.
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