Thèse de doctorat : Mathématiques : Lyon, École normale supérieure (sciences) : 2006. / Bibliogr. p. [155]-159. Index.

Not available / text

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Jacques Distler. Vita. Includes bibliographical references. Also available from UMI.

Cette thèse se propose d'étudier sous divers points de vue les groupes d'automorphismes d'immeubles. Un de ses objectifs est de mettre en valeur les différences autant que les analogies entre les immeubles affines et non affines. Pour appuyer cette dichotomie, on y démontre que les groupes d'automorphismes d'immeubles non affines n'ont jamais de paire de Gelfand, contrairement aux immeubles affines. Dans l'autre sens, pour souligner l'analogie entre immeubles affines et non affines, on définit une nouvelle notion de bord combinatoire d'un immeuble. Dans le cas des immeubles affines, ce bord s'identifie au bord polyédral. On relie la construction de ce bord à d'autres constructions déjà existantes, par exemple, la compactification de Busemann du graphe des chambres. La compactification combinatoire est également isomorphe à la compactification par la topologie de Chabauty de l'ensemble des chambres, sous des hypothèses de transitivité. On relie aussi le bord combinatoire à un autre espace, généralisant une construction de F. Karpelevic pour les espaces symétriques : celle du bord raffiné d'un espace CAT(0).On démontre alors que les points du bord paramètrent les sous-groupes moyennables maximaux de l'immeuble, à indice fini près. Enfin, on prouve que l'action du groupe d'automorphismes d'un immeuble localement fini sur le bord combinatoire de ce dernier est moyennable, fournissant ainsi des résolutions en cohomologie bornée et des applications bord explicites. Ceci donne aussi une nouvelle preuve que ces groupes satisfont la conjecture de Novikov. / The object of this thesis is the study, from different point of views, of automorphism groups of buildings. One of its objectives is to highlight the differences as well as the analogies between affine and non-affine buildings. In order to support this dichotomy, we prove that automorphism groups of non-affine buildings never have a Gelfand pair, contrarily to affine buildings.In the other direction, the analogy between affine and non-affine buildings is supported by the new construction of a combinatorial boundary of a building. In the affine case, this boundary is in fact the polyhedral boundary. We connect the construction of this boundary to other compactifications, such as the Busemann compactification of the graph of chambers. The combinatorial compactification is also isomorphic to the group-theoretic compactification, which embeds the set of chambers into the set of closed subgroups of the automorphism group. We also connect the combinatorial boundary to another space, which generalises a construction of F. Karpelevic for symmetric spaces : the refined boundary of a CAT(0) space.We prove that the maximal amenable subgroups of the automorphism group are, up to finite index, parametrised by the points of the boundary. Finally, we prove that the action of the automorphism group of a locally finite building on its combinatorial boundary is amenable, thus providing resolutions in bounded cohomology and boundary maps. This also gives a new proof that these groups satisfy the Novikov conjecture.

In this thesis, we study compactifiations of ten-dimensional heterotic supergravity at O(α'), focusing on the moduli of such compactifications. We begin by studying supersymmetric compactifications to four-dimensional maximally symmetric space, commonly referred to as the Strominger system. The compactifications are of the form M₁₀ = M₄ x X, where M₄ is four-dimensional Minkowski space, and X is a six-dimensional manifold of what we refer to as heterotic SU(3)-structure. We show that this system can be put in terms of a holomorphic operator D on a bundle Q = T* X ⊕ End(TX) ⊕ End(V ) ⊕ TX, defined by a series of extensions. Here V is the E₈ x E₈ gauge-bundle, and TX is the tangent bundle of the compact space X. We proceed to compute the infinitesimal deformation space of this structure, given by TM = H^(0,1)(Q), which constitutes the infinitesimal spectrum of the lower energy four-dimensional theory. In doing so, we find an over counting of moduli by H^(0,1)(End(TX)), which can be reinterpreted as O(α') field redefinitions. In the next part of the thesis, we consider non-maximally symmetric compactifications of the form M₁₀ = M₃ x Y , where M₃ is three-dimensional Minkowski space, and Y is a seven-dimensional non-compact manifold with a G₂-structure. We write X → Y → ℝ, where X is a six dimensional compact space of half- at SU(3)-structure, non-trivially fibered over ℝ. These compactifications are known as domain wall compactifications. By focusing on coset compactifications, we show that the compact space X can be endowed with non-trivial torsion, which can be used in a combination with %α'-effects to stabilise all geometric moduli. The domain wall can further be lifted to a maximally symmetric AdS vacuum by inclusion of non-perturbative effects in a heterotic KKLT scenario. Finally, we consider domain wall compactifications where X is a Calabi-Yau. We show that by considering such compactifications, one can evade the usual no-go theorems for flux in Calabi-Yau compactifications, allowing flux to be used as a tool in such compactifications, even when X is Kähler. The ultimate success of these compactifications depends on the possibility of lifting such vacua to maximally symmetric ones by means of e.g. non-perturbative effects.

Cette thèse se propose d'étudier sous divers points de vue les groupes d'automorphismes d'immeubles. Un de ses objectifs est de mettre en valeur les différences autant que les analogies entre les immeubles affines et non affines. Pour appuyer cette dichotomie, on y démontre que les groupes d'automorphismes d'immeubles non affines n'ont jamais de paire de Gelfand, contrairement aux immeubles affines. Dans l'autre sens, pour souligner l'analogie entre immeubles affines et non affines, on définit une nouvelle notion de bord combinatoire d'un immeuble. Dans le cas des immeubles affines, ce bord s'identifie au bord polyédral. On relie la construction de ce bord à d'autres constructions déjà existantes, par exemple, la compactification de Busemann du graphe des chambres. La compactification combinatoire est également isomorphe à la compactification par la topologie de Chabauty de l'ensemble des chambres, sous des hypothèses de transitivité. On relie aussi le bord combinatoire à un autre espace, généralisant une construction de F. Karpelevic pour les espaces symétriques : celle du bord raffiné d'un espace CAT(0).On démontre alors que les points du bord paramètrent les sous-groupes moyennables maximaux de l'immeuble, à indice fini près. Enfin, on prouve que l'action du groupe d'automorphismes d'un immeuble localement fini sur le bord combinatoire de ce dernier est moyennable, fournissant ainsi des résolutions en cohomologie bornée et des applications bord explicites. Ceci donne aussi une nouvelle preuve que ces groupes satisfont la conjecture de Novikov.

The aim of this thesis is to establish the principal properties for the theory of ordered compactifications relating to connectedness and to provide particular examples. The initial idea of this subject is based on the notion of the Stone-Cech compactification.The ordered Stone-Cech compactification oX of an ordered topological space X is constructed analogously to the Stone-Cech compactification X of a topological space X, and has similar properties. This technique requires a conceptual understanding of the Stone-Cech compactification and how its product applies to the construction of ordered topological spaces with continuous increasing functions. Chapter 1 introduces background information. Chapter 2 addresses connectedness and compactification. If (A;B) is a separation ofa topological space X, then (A 8 B) = A 8 B, but in the ordered setting, o(A 8 B)need not be oA 8 oB. We give an additional hypothesis on the separation (A;B) tomake o(A 8 B) = oA 8 oB. An open question in topology is when is X -X = X. Weanswer the analogous question for ordered compactifications of totally ordered spaces. So, we are concerned with the remainder, that is, the set of added points oX -X. Wedemonstrate the topological properties by using lters. Moreover, results of lattice theory turn out to be some of the basic tools in our original approach. In Chapter 3, specific examples and counterexamples are given to illustrate earlierresults.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Physics and Astronomy." Includes bibliographical references (p. 165-172).

Orientifolds of type II string theory offer a promising toolkit for model builders, especially when one includes not only the usual fluxes from NSNS and RR field strengths, but also fluxes that are T-dual to the NSNS three-form flux. These additional ingredients can help stabilize moduli and lead to D-term contributions to the effective scalar potential. We describe in general how these fluxes appear as parameters of an effective N = 1 supergravity theory in four dimensions for type IIA and type IIB string theory. We also show how these fluxes arise from compactifications on six-dimensional spaces that can be described by toroidal fibers twisted over a toroidal base. This approach leads us to a more subtle treatment of the quantization of the general NSNS fluxes. We illustrate these phenomena with examples of certain orientifolds of T⁶/Z₄. / text