We study the Neumann problem for the de Rham complex in a bounded domain of Rn with singularities on the boundary. The singularities may be general enough, varying from Lipschitz domains to domains with cuspidal edges on the boundary. Following Lopatinskii we reduce the Neumann problem to a singular integral equation of the boundary. The Fredholm solvability of this equation is then equivalent to the Fredholm property of the Neumann problem in suitable function spaces. The boundary integral equation is explicitly written and may be treated in diverse methods. This way we obtain, in particular, asymptotic expansions of harmonic forms near singularities of the boundary.

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In this thesis, we investigate sigma models and algebraic structures emerging from a Hamiltonian description of their dynamics, both in a classical and in a quantum setup. More specifically, we derive the phase space structures together with the Hamiltonians for the bosonic two-dimensional non-linear sigma model, and also for the N=1 and N=2 supersymmetric models. A convenient framework for describing these structures are Lie conformal algebras and Poisson vertex algebras. We review these concepts, and show that a Lie conformal algebra gives a weak Courant–Dorfman algebra. We further show that a Poisson vertex algebra generated by fields of conformal weight one and zero are in a one-to-one relationship with Courant–Dorfman algebras. Vertex algebras are shown to be appropriate for describing the quantum dynamics of supersymmetric sigma models. We give two definitions of a vertex algebra, and we show that these definitions are equivalent. The second definition is given in terms of a λ-bracket and a normal ordered product, which makes computations straightforward. We also review the manifestly supersymmetric N=1 SUSY vertex algebra. We also construct sheaves of N=1 and N=2 vertex algebras. We are specifically interested in the sheaf of N=1 vertex algebras referred to as the chiral de Rham complex. We argue that this sheaf can be interpreted as a formal quantization of the N=1 supersymmetric non-linear sigma model. We review different algebras of the chiral de Rham complex that one can associate to different manifolds. In particular, we investigate the case when the manifold is a six-dimensional Calabi–Yau manifold. The chiral de Rham complex then carries two commuting copies of the N=2 superconformal algebra with central charge c=9, as well as the Odake algebra, associated to the holomorphic volume form.

Wir fixeren einen Körper k, der bezüglich eines nicht-archimedischen Absolutbetrags vollständig ist. In Kapitel 1 konstruieren wir eine Algebra U bestehend aus überkonvergenten Funktionen. Sie ist eine Unteralgebra der Tate-Algebra, wobei mittels einer sogenannten Filterfunktion, eine zusätzliche Wachstumsbedingung an die Koeffizienten der Potenzreihen in U gestellt wird. In diesem Kontext beweisen wir das folgende Resultat: U ist ein Noetherscher, Jacobsonscher, faktorieller Integritätsbereich, der bezüglich der Norm vollständig ist, und jedes Ideal in U ist abgeschlossen in der induzierten Topologie. In Kapitel 2 definieren wir die Kategorie der NMK-Algebren als die Kategorie der Quotienten der U. Indem wir in der größeren Kategorie der Frèchet-Räume arbeiten, beweisen wir die Noethernormalisierung und untersuchen die Morphismen zwishen NMK-Algebren. Schließlich zeigen wir, dass die Kategorie der NMK-Algebren abgeschlossen ist unter vervollständigten Tersorprodukten. In Kapitel 3 untersuchen wir geometrische Aspekte der Algebren U nämlich Eigenschaften der maximalen Ideale und die Regularität von U. Abschließend zeigen wir, dass für jedes U der assoziierte algebraische v exact in positiven Graden ist. / We fix a complete field k with respect to a non-Archimedean absolute value. In Chapter 1, we build the overconvergent function algebra U to be the subalgebra of the Tate algebra by putting a growth condition on the coefficients of the power series using a decreasing function which we call a filter function (satisfying certain conditions). With this setting we prove the following result: U is a Noetherian, Jacobson, unique factorization domain and it is complete with respect to the norm on it, moreover every ideal of U is closed with respect to the induced topology. In Chapter 2, we define a category of NMK-algebras as the category of all quotients of U. Working in the larger category of Frèchet spaces, we establish Noether normalization and investigate the morphisms between NMK-algebras. Finally, we show that the category of NMK-algebras is closed under completed tensor products. We investigate certain geometric aspects of the algebra U in Chapter 3, such as the properties of maximal ideals and regularity of U. Further, we show that for each U the associated algebraic de Rham complex is exact in positive degrees.

This work deals with the application of supermathematics to supersymmetrical problems arising in physics. Some recent developments are presented in detail. A reduction scheme for general supermanifolds to vector bundles is presented, which significantly simplifies their mathematical treatment in a physical context. Moreover, some applications of this new approach are worked out, such as the Fermi oscillator. / text

O objetivo deste texto é apresentar uma classe de módulos para álgebra de Lie de campos vetoriais em um toro N -dimensional, Vect( T N ). O caso N = 1 nos dá a famosa álgebra de Witt (sua extensão central é álgebra de Virasoro). A álgebra Vect( T N ) apresenta um classe de módulos parametrizada por módulos de dimensão finita da álgebra gl N . Nosso objeto central de estudo são módulos induzidos dos módulos tensoriais de Vect( T N ) para Vect( T N +1 ). Estes módulos apresentam um quociente irredutível com espaços de peso de dimensão finita. A álgebra Vect( T N ) apresenta como subálgebra sl N +1 . Com a restrição da ação de Vect( T N ) a esta subálgebra obtemos o carácter deste quociente. Para obter um critério de irredutibilidade e construir sua realização de campo livre, consideramos uma classe de módulos para 1 (T N +1 )/ d 0 (T N +1 ) o Vect (T N ) , construída a partir de álgebras de vértice. Quando restritos a Vect (T N ) estes módulos continuam irredutíveis a menos que apareçam no chiral de De Rham. / The goal of this text is to present a class of modules for the Lie algebra of vector fields in a N -dimensional torus, Vect (T N ) . The case N = 1 give us the famous Witt algebra (its central extension is the Virasoro algebra). The algebra Vect( T N ) has a class of modules parametrized by finite dimensional gl N -modules. The central object of our study are modules induced from tensor modules for Vect( T N ) to Vect( T N +1 ). Those modules have an irreducible quotient such that every weight space has finite dimension. The algebra Vect( T N ) has as subalgebra sl N +1 . Restricting the action of Vect( T N ) to this subálgebra we have the character of this quotient. To obtain a irreducible critreria and construct a free field reazilation, we consider a class of modules for 1 (T N +1 )/ d 0 (T N +1 ) o Vect (T N ) , constructed from vertex algebras. When restricted to Vect (T N ) thesse modules remain irreducible, unless they belongs to the chiral De Rham complex.

Made available in DSpace on 2016-06-02T20:27:39Z (GMT). No. of bitstreams: 1 3703.pdf: 612745 bytes, checksum: 57763528b5a111b975b1122e35bbc887 (MD5) Previous issue date: 2011-06-16 / Universidade Federal de Minas Gerais / In this work, we extend some global L1 estimates proved by Bourgain-Brezis in the case of the de Rham complex on RN to the setup of local L1 estimates for elliptic complexes, namely, those associated to involutive elliptic structures spanned by a family of linearly independent smooth complex vector fields. In particular, we obtain a local version of Gagliardo-Nirenberg estimates for elliptic systems of vector fields. / Neste trabalho, estendemos algumas estimativas L1 provadas por Bourgain-Brezis no caso do complexo de de Rham em RN para o contexto local de estimativas L1 para complexos elíticos, a saber, aqueles associados a uma estrutura involutiva elítica gerada por uma família de campos vetoriais suaves e linearmente independentes. Em particular, obtemos uma versão local da desigualdade de Gagliardo-Nirenberg para um sistema de campos vetoriais elíticos.

Dans cette thèse, d’une part, nous généralisons au cas équivariant un résultat de J. Denef et F. Loeser sur les sommes trigonométriques sur un tore ; d’autre part, nous étudions la stratification de Thom-Boardman associée à la multiplication des sections globales des fibrés en droites sur une courbe. Nous montrons une inégalité subtile sur les dimensions de ces strates. Notre motivation vient du programme de Langlands géométrique. En s’appuyant sur les travaux de W. T. Gan, N. Gurevich, D. Jiang et de S. Lysenko, nous proposons, pour le groupe réductif G de type G2, une construction conjecturale du faisceau automorphe dont le paramètre d’Arthur est unipotent et sous-régulier. En utilisant nos deux résultats ci-dessus, nous déterminons les rangs génériques de toutes les composantes isotypiques d’un faisceau S₃-équivariant qui apparaît dans notre conjecture, ce S₃ étant le centralisateur du SL2 sous-régulier dans le groupe dual de Langlands de G. / In this thesis, on the one hand, we generalise to the equivariant case a result of J. Denef and F. Loeser about trigonometric sums on tori ; on the other hand, we study the Thom-Boardman stratification associated to the multiplication of global sections of line bundles on a curve. We prove a subtle inequaliity about the dimensions of these strata. Our motivation comes from the geometric Langlands program. Based on works of W. T. Gan, N. Gurevich, D. Jiang and S. Lysenko, we propose, for the reductive group G of type G2, a conjectural construction of the automorphic sheaf whose Arthur parameter is unipotent and sub-regular. Using our two results above, we determine the generic ranks of all isotypic components of an S3-equivaraint sheaf which appears in our conjecture, this S3 being the centraliser of the sub-regular SL2 inside the Langlands dual group of G.