Key information / Informations

•    Funding programme / Programme de financement: H2020 - ERC Advanced Grant - 2016
•    Coordinator / Coordinateur: Pr Thomas BUCHERT
•    Partners’ list / Liste des partenaires : NA
•    Budget : 2 091 000,00€
•    Grant / Subvention : 2 091 000,00€
•    Début – Fin : 2017-2022

Context / Contexte

The project ARTHUS aims at determining the physical origin of Dark Energy: in addition to the energy sources of the standard model of cosmology, effective terms arise through spatially averaging inhomogeneous cosmological models in General Relativity. It has been demonstrated that these additional terms can play the role of Dark Energy on large scales (but they can also mimic Dark Matter on scales of mass accumulations). The underlying rationale is that fluctuations in the Universe generically couple to spatially averaged intrinsic properties of space, such as its averaged scalar curvature, thus changing the global evolution of the effective (spatially averaged) cosmological model. At present, we understand these so-called backreaction effects only qualitatively.

Objectives / Objectifs

ARThUs investigates three Main Research Axes (each containing five workpackages - WPs): (i) the investigation of explicit models for structure formation in relativistic cosmology (Axis A), (ii) the robust statistical analysis and reinterpretation of observational data within the new framework (Axis B), and (iii) fundamental questions of averaging strategies (Axis C). Here, we shall also address problems of the Early Universe (inflation), and we shall spend a considerable effort on the generalization of the averaging scheme itself.
Axis A : Structure formation models in General Relativity (analytical approaches; investigation of the average properties)
Axis B : Inhomogeneities in observed structure (numerical and statistical analysis of observations and their reinterpretation)
Axis C : Advances in fundamental questions (the averaging problem, effective scalar field models)

Expected impact and results / Impact et résultats attendus

The project ARTHUS is directed towards a conclusive quantitative evaluation of these effects by developing generic and non-perturbative relativistic models of structure formation, by statistically measuring the key variables of the models in observations and in simulation data, and by reinterpreting observational results in light of the new models. It is to be emphasized that there is no doubt about the existence of backreaction effects; the question is whether they are even capable of getting rid of the dark sources (as some models discussed in the literature suggest), or whether their impact is substantially smaller. The project thus addresses an essential issue of current cosmological research: to find pertinent answers concerning the quantitative impact of inhomogeneity effects, a necessary, worldwide recognized step toward high-precision cosmology. If the project objectives are attained, the results will have a far-reaching impact on theoretical and observational cosmology, on the interpretation of astronomical experiments such as Planck and Euclid, as well as on a wide spectrum of particle physics theories and experiments.

LIP’s contribution / Rôle de LIP

LIP a accompagné le porteur de projet dans toute la phase de montage, coordination du montage administratif et financier du projet, conseil à la rédaction. LIP accompagne l’Université Lyon 1 pour le suivi administratif et financier du projet