Dark-energy dependent test of general relativity at cosmological scales

The $\Lambda$CDM framework offers a remarkably good description of our universe with a very small number of free parameters, which can be determined with high accuracy from currently available data. However, this does not mean that the associated physical quantities, such as the curvature of the universe, have been directly measured. Similarly, general relativity is assumed, but not tested. Testing the relevance of general relativity for cosmology at the background level includes a verification of the relation between its energy contents and the curvature of space. Using an extended Newtonian formulation, we propose an approach where this relation can be tested. Using the recent measurements on cosmic microwave background, baryonic acoustic oscillations and the supernova Hubble diagram, we show that the prediction of general relativity is well verified in the framework of standard $\Lambda$CDM assumptions, i.e. an energy content only composed of matter and dark energy, in the form of a cosmological constant or equivalently a vacuum contribution. However, the actual equation of state of dark fluids cannot be directly obtained from cosmological observations. We found that relaxing the equation of state of dark energy opens a large region of possibilities, revealing a new type of degeneracy between the curvature and the total energy content of the universe.Comment: 5 pages, 3 figures. Accepted for publication in Physical Review

Dark sectors of the Universe: A Euclid survey approach

In this paper we study the consequences of relaxing the hypothesis of the pressureless nature of the dark matter component when determining constraints on dark energy. To this aim we consider simple generalized dark matter models with constant equation of state parameter. We find that present-day low-redshift probes (type-Ia supernovae and baryonic acoustic oscillations) lead to a complete degeneracy between the dark energy and the dark matter sectors. However, adding the cosmic microwave background (CMB) high-redshift probe restores constraints similar to those on the standard $\Lambda$CDM model. We then examine the anticipated constraints from the galaxy clustering probe of the future Euclid survey on the same class of models, using a Fisher forecast estimation. We show that the Euclid survey allows us to break the degeneracy between the dark sectors, although the constraints on dark energy are much weaker than with standard dark matter. The use of CMB in combination allows us to restore the high precision on the dark energy sector constraints.Comment: 10 pages, 6 figure

Cosmological constraints in Lambda-CDM and Quintessence paradigms with Archeops

We review the cosmological constraints put by the current CMB experiment including the recent ARCHEOPS data, in the framework of Lambda-CDM and quintessence paradigm. We show that well chosen combinations of constraints from different cosmological observations lead to precise measurements of cosmological parameters. The Universe seems flat with a 70 percents contribution of dark energy with an equation of state very close to those of the vacuum.Comment: to appear in New Astronomy Reviews, Proceedings of the CMBNET Meeting, 20-21 February 2003, Oxford, U

Mesure de la section efficace de photoproduction de beaute en photons reels

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 20522 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

CONCEPTION ET MISE AU POINT DE LA PROCEDURE DE QUALIFICATION DU CALORIMETRE ELECTROMAGNETIQUE A ARGON LIQUIDE DU DETECTEUR ATLAS

CHAMBERY -BU Bourget (730512101) / SudocSudocFranceF

What can be learned about dark energy evolution?

Accepted in Astronomy and Astrophysics; new version: data updated, conclusion unchanged.We examine constraints obtained from SNIa surveys on a two parameter model of dark energy in which the equation of state $w (z) = P(z) / \rho (z)$ undergoes a transition over a period significantly shorter than the Hubble time. We find that a transition between $w \sim -0.2$ and $w \sim -1$ (the first value being somewhat arbitrary) is allowed at redshifts as low as $0.1$, despite the fact that data extend beyond $z \sim 1$. Surveys with the precision anticipated for space experiments should allow only slight improvement on this constraint, as a transition occurring at a redshift as low as $\sim 0.17$ could still remain undistinguishable from a standard cosmological constant. The addition of a prior on the matter density \Omega_\MAT = 0.3 only modestly improves the constraints. Even deep space experiments would still fail to identify a rapid transition at a redshift above $0.5$. These results illustrate that a Hubble diagram of distant SNIa alone will not reveal the actual nature of dark energy at a redshift above $0.2$ and that only the local dynamics of the quintessence field can be infered from a SNIa Hubble diagram. Combinations, however, seem to be very efficient: we found that the combination of present day CMB data and SNIa already excludes a transition at redshifts below $0.8$