# Flot de Ricci sans borne supérieure sur la courbure et géométrie de certains espaces métriques

Abstract : The Ricci flow was introduced by Hamilton in the beginning of the 90's. It has been a valuable tool to study the topology and the geometry of smooth Riemannian manifolds. For example, it was essential in the of the Poincaré conjecture (Perelman, 2003) and of the differentiable sphere theorem (Brendle and Schoen, 2008). In this thesis, we are interested in the applications of Ricci flow to metric spaces with curvature bounded from below which are not smooth. We define what it means for a Ricci flow to admit a metric space as initial condition. In Chapter 2, we present some works of Simon which allow to build a Ricci flow for some metric spaces of dimension 3. We also give two applications of this result : a finiteness theorem in dimension 3 and an alternative of a theorem of Cheeger and Colding in dimension 3. In Chapter 3, we treat the special case of dimension 2. We show that for singular surfaces whose curvature is boded from below (in the sense of Alexandrov), we can define a Ricci and it is unique. This allow to show that for surfaces with curvature bounded from below, the application which maps a surface to its Ricci flow is continuous with respect to Gromov-Hausdorff perturbations of the initial condition. Chapter 4 generalizes some of these methods in higher dimension. Here one needs to consider other conditions on the curvature than the usual "Ricci curvature bounded from below" and "sectional curvature bounded from below". The methods used there allow us to build a Ricci flow for some non-collapsed metric spaces which are limits of manifolds whose curvature operator is bounded from below. We also show that under some non-collapsing assumptions manifolds with almost non-negative curvature operator admit metrics with non-negative curvature operator.
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Submitted on : Thursday, December 20, 2012 - 6:29:09 PM
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Thomas Richard. Flot de Ricci sans borne supérieure sur la courbure et géométrie de certains espaces métriques. Autre [q-bio.OT]. Université de Grenoble, 2012. Français. ⟨NNT : 2012GRENM038⟩. ⟨tel-00768066⟩

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