Empreintes de l'Énergie Noire sur la structuration de l'Univers

Vincent Bouillot 1
1 Cosmologie: Origine et Structures
LUTH - Laboratoire Univers et Théories
Abstract : This thesis is dedicated to the research of specific imprints of Dark Energy in both linear and non-linear gravitational collapse processes through theoretical and numerical developments. Indeed, many aspects of cosmology has been tackled: first, to study the influence of various complex Dark Energy models on the halo clustering, we develop in a covariant formalism the usual linear cosmological perturbation theory. It gives an extent of the classical Sasaki-Mukhanov equations to scalar fields coupled with multiple cosmological fluids. The result is the description of the evolution of linear perturbations of complex Dark Energy models with a minimal number of degrees of freedom. In the last decade, the number and quality of cosmological observations on the matter distribution in the Universe as well on the velocity fields have increased exponentially. In particular, recent measurements show the existence of abnormally high velocity fields with respect to the linear theory in $\Lambda$CDM. The explanation of this cosmic flow excess at intermediate scales is the main contribution of this thesis: reinterpreting the anomalous cosmic flow (Watkins et al.) measured at scales ~50 Mpc/h as a rare event realization in linear theory, we propose a new cosmological probe. This probe uses the scale of convergence of the measured cosmic flow with the theoretical one. We develop the sensibility on this new cosmological probe in three competitive Dark Energy models. Those results, based on analytical methods, are compared with measures issued from state-of-the-art numerical simulations we're deeply involved in. Then, starting from those numerical simulations, we investigate the dynamical origin of such a cosmic flow: we prove this movement to be due to an asymmetry of the three-dimensional matter distribution at higher scales (80 Mpc/h). This asymmetry is shown by introducing an original estimator of the matter field, which quantify the deviation from symmetry of a given field. Finally, we demonstrate that the spatial arrangement of the environments presenting such an anomalous cosmic flow in the Universe is correlated with the density peak distribution. This correlation indicates in a local way the structures distribution responsible for the anomalously high cosmic flow. An another way to understand Dark Energy is to use density field instead of velocity fields. In particular, we characterize the density field in terms of correlation function. In this thesis, we present many promising results to understand the role of Dark Energy in halo and galaxy clustering from correlation function measurements issued from the Dark Energy Universe Simulation Series (DEUSS). On the one hand, this is achieved by introducing a mass segregation for correlation functions. On the other hand, this is reached by considering the difference between comoving space and redshifts space. The emphasize is laid on two particular sides of this problematic. First, we underline the impact of correlation measures on the bias in cosmology: it give many results on the dependence of this bias on the cosmological model and the redshift. Then, those measurements prove that the imprint of Dark Energy on the non-linear regime of structures formation in the Universe, already shown on the continuous matter field, remains on dark matter halo correlation function. Finally, this thesis presents a lot of improvements done in numerical cosmology. In particular, the realization of the DEUSS: Full Universe Runs simulations, first numerical modeling of the whole observable Universe from Big Bang to nowadays, triggers the optimization of all cosmological codes used. This set of simulations has already given striking results, using an unprecedented statistics. The numerical methods used to follow the gravitational collapse of a density field and detect structures and their various optimizations are presented in a numerical part at the end of the thesis.
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Vincent Bouillot. Empreintes de l'Énergie Noire sur la structuration de l'Univers. Cosmologie et astrophysique extra-galactique [astro-ph.CO]. Observatoire de Paris, 2012. Français. ⟨tel-00783033⟩

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