Thesis (Ph. D.)--University of Chicago, Dept. of Mathematics, June 1999. / Includes bibliographical references. Also available on the Internet.

This licentiate thesis consists of two papers. In paper I the tautological ring of a Hilbert modular variety at an unramified prime is computed. The method of van der Geer in the case of A_{g} is extended to deal with the case of the Hilbert modular variety, which is more complicated. An example involving the unitary group is given which shows that this method cannot be used to compute the tautological rings of all Shimura varieties of Hodge type. In paper II we compute the pushforward map from a sub flag variety defined by a Levi subgroup to the Siegel flag variety. Specifically, this is the Levi factor of the parabolic associated with the maximal rational boundary component of the Siegel Shimura datum. The method involves an explicit understanding of the pullback map and an application of the self intersection formula.

Motivated by the example of the tangent bundle of a stratified space, which is no longer a vector bundle, we begin the construction of a general theory of smooth stratified vector bundles. We show that one can construct a frame bundle of a smooth stratified vector bundle in a canonical way, but that there are substantial obstructions to constructing an orthonormal frame bundle. / Master of Science / Smooth manifolds are the natural class of spaces on which we can perform the normal operations of calculus. There have been many efforts to generalize the class of spaces on which one can perform these operations. One possible class are stratified spaces, which are spaces that are built out of smooth manifolds in sufficiently nice ways. Spaces such as vector bundles and their frame bundles play a central role in the smooth manifold theory, and here we begin the development of the appropriate corresponding theory for stratified spaces.

In this thesis we study some questions related to vector bundles over hypersurfaces. More precisely, for hypersurfaces of dimension ≥ 2, we study the extension problem of vector bundles. We find some cohomological conditions under which a vector bundle over an ample divisor of non-singular projective variety, extends as a vector bundle to an open set containing that ample divisor. Our method is to follow the general Groethendieck-Lefschetz theory by showing that a vector bundle extension exists over various thickenings of the ample divisor. For vector bundles of rank > 1, we find two separate cohomological conditions on vector bundles which shows the extension to an open set containing the ample divisor. For the case of line bundles, our method unifies and recovers the generalized Noether-Lefschetz theorems by Joshi and Ravindra-Srinivas. In the last part of the thesis, we make a specific study of vector bundles over elliptic curve.

In this thesis we study various ways in which every two general points on a variety can be connected by curves of a fixed genus, thus mimicking the notion of a rationally connected variety but for arbitrary genus. We assume the existence of a covering family of curves which dominates the product of a variety with itself either by allowing the curves in the family to vary in moduli, or by assuming the family is trivial for some fixed curve of genus g. A suitably free curve will be one with a large unobstructed deformation space, the images of whose deformations can join any number of points on a variety. We prove that, at least in characteristic zero, the existence of such a free curve of higher genus is equivalent to the variety being rationally connected. If one restricts to the case of genus one, similar results can be obtained even allowing the curves in the family to vary in moduli. In later chapters we study algebraic properties of such varieties and discuss attempts to prove the same rational connectedness result in positive characteristic.

No description available.

Wir studieren Moduln über Maximalordnungen auf glatten projektiven Flächen und ihre Modulräume. Wir untersuchen null- und zweidimensionale Modulräume auf K3 und abelschen Flächen für unverzweigte Ordnungen, den sogenannten Azumaya Algebren. Weiterhin untersuchen wir Modulräume für spezielle verzweigte Ordnungen auf der projektiven Ebene. Wir beweisen das diese Räume immer glatt sind. Mit Hilfe dieses Ergebnisses studieren wir die Deformationstheorie der betrachteten Moduln. Im letzten Kapitel konstruieren wir explizite Ordnungen und berechnen einige Modulräume.

Orientador: Marcos Benevenuto Jardim / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica / Made available in DSpace on 2018-08-17T21:21:11Z (GMT). No. of bitstreams: 1 Santos_RodrigoPiresdos_M.pdf: 1008454 bytes, checksum: e5ec1fd87b26efb201ece05c20531374 (MD5) Previous issue date: 2011 / Resumo: Apresentamos uma introdução aos conceitos de geometria complexa necessários à compreensão da correspondência Hitchin-Kobayashi. Enunciamos e provamos que todo fibrado que admite uma conexão de Hermite-Einstein é poliestável. Em seguida, discutimos resultados sobre Q-fibrados e enunciamos uma correspondência Hitchin-Kobayashi para esse caso. Por último, temos um resultado do autor que relaciona a estabilidade de fibrados com a estabilidade de Q-fibrados / Abstract: We present an introduction to the concepts of complex geometry necessary to the comprehension of the Hitchin-Kobayashi correspondence. We state and prove that every holomorphic vector bundle which admits a Hermite-Einstein connexion is polystable. Then, we discuss results regarding quiver bundles and state a Hitchin-Kobayashi correspondence for this case. Finally, we state and prove an author's result which relates the stability of vector bundles with the stability of quiver bundles / Mestrado / Geometria Diferencial / Mestre em Matemática

Orientador: Marcos Benevenuto Jardim / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica / Made available in DSpace on 2018-08-24T04:44:46Z (GMT). No. of bitstreams: 1 Silva_VitorMorettoFernandesda_D.pdf: 591420 bytes, checksum: aa507d8eca04760207f4e88b0636be83 (MD5) Previous issue date: 2013 / Resumo: Neste trabalho estudamos uma equivalência entre mônadas e representações de quivers. No segundo capítulo apresentamos um critério de decomponibilidade para mônadas lineares e, em particular, para instantons. No terceiro capítulo apresentamos exemplos de mônadas sobre espaços projetivos de dimensão par que generalizam a mônada de Horrocks-Mumford em P4 / Abstract: In this work, we study an equivalence between monads and representations of quivers. The second chapter presents a decomposability criterion for linear monads and, in particular, for instantons. In the third chapter we present new examples of monads on projective spaces of even dimension, which generalize the Horrocks-Mumford monad on P4 / Doutorado / Matematica / Doutor em Matemática

Soit X une courbe projective lisse et irréductible munie d'une involution σ. Dans cette thèse, nous étudions les fibrés vectoriels invariants and anti-invariants sur X sous l'action induite par σ. On introduit la notion de modules σ-quadratiques et on l'utilise, avec GIT, pour construire ces espaces de modules, puis on en étudie certaines propriétés. Ces espaces de modules correspondent aux espaces de modules de G-torseurs parahoriques sur la courbe X/σ , pour certains schémas en groupes parahoriques G de type Bruhat-Tits, qui sont twistés dans le cas des anti-invariants. Nous développons les systèmes de Hitchin sur ces espaces de modules et on les utilise pour dériver une classification de leurs composantes connexes en les dominant par des variétés de Prym. On étudie aussi le fibré déterminant sur les espaces de modules des fibrés vectoriels anti-invariants. Dans certains cas, ce fibré en droites admet certaines racines carrées appelées fibrés Pfaffiens. On montre que les espaces des sections globales des puissances de ces fibrés en droites (les espaces des fonctions thêta généralisées) peuvent être canoniquement identifier avec les blocs conformes associés aux algèbres de Kac-Moody affines twistées de type A(2). / Let X be a smooth irreducible projective curve with an involution σ. In this dissertation, we studythe moduli spaces of invariant and anti-invariant vector bundles over X under the induced action of σ. We introduce the notion of σ-quadratic modules and use it, with GIT, to construct these moduli spaces, and than we study some of their main properties. It turn out that these moduli spaces correspond to moduli spaces of parahoric G-torsors on the quotient curve X/σ, for some parahoric Bruhat-Tits group schemes G, which are twisted in the anti-invariant case.We study the Hitchin system over these moduli spaces and use it to derive a classification of theirconnected components using dominant maps from Prym varieties. We also study the determinant of cohomology line bundle on the moduli spaces of anti-invariant vector bundles. In some cases this line bundle admits some square roots called Pfaffian of cohomology line bundles. We prove that the spaces of global sections of the powers of these line bundles (spaces of generalized theta functions) can be canonically identified with the conformal blocks for some twisted affine Kac-Moody Lie algebras of type A(2).