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Theses

Cosmologies spatialement homogènes en théories tenseur-scalaires

Abstract : This thesis studies the homogeneous but anisotropic cosmological models in scalar-tensor theories. Its goal is to determine the properties of these theories so that these models asymptotically behave as our current Universe or bring some responses to some of its problems like the cosmological constant or coincidence problems. The first part of the thesis is devoted to a historical introduction and a physical justification of the scalar-tensor theories and anisotropic cosmological models. The second part details the mathematical tools, necessary to understand this thesis, namely anisotropic cosmologies classification and the form of the field equations in the Lagrangian and Hamiltonian formalism. The third part is made up of a series of seven published papers and shows how one can constraint the scalar-tensor theories using exact solutions, requiring some dynamical characteristics for the Universe(expansion, inflation, etc), preventing the singularity occurence or showing Noether symmetries. In the fourth part, the isotropisation process of the anisotropic models is studied in detail for many classes of scalar-tensor theories. Necessary constraints for isotropisation, the asymptotic behaviors of the metric functions and potential in the vicinity of this state are determined and the quintessence phenomenon is analyzed. A link between quintessent scalar fields which could populate our Universe and dark matter in the galaxies is shown. The six papers at the origin of this chapter are reproduced in the sixth part. We conclude in the fifth part.
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Submitted on : Friday, January 14, 2005 - 12:04:52 PM
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Stéphane Fay. Cosmologies spatialement homogènes en théories tenseur-scalaires. Cosmologie et astrophysique extra-galactique [astro-ph.CO]. Université Paris-Diderot - Paris VII, 2004. Français. ⟨tel-00008063⟩

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