In this thesis we present the connection between vertex operator algebras and modular forms which lies at the heart of Borcherds’ proof of the Monstrous Moonshine conjecture. In order to do so we introduce modular forms, vertex algebras, vertex operator algebras and their partition functions. Each notion is illustrated with examples.

vii, 41 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / We generalize a theorem of Zhu relating the trace of certain vertex algebra representations and modular invariants to the arena of vertex super algebras. The theorem explains why the space of simple characters for the Neveu-Schwarz minimal models NS( p, q ) is modular invariant. It also expresses negative products in terms of positive products, which are easier to compute. As a consequence of the main theorem, the subleading coefficient of the singular vectors of NS( p, q ) is determined for p and q odd. An interesting family of q -series identities is established. These consequences established here generalize results of Milas in this field. / Adviser: Arkady Vaintrob

This thesis consists of two parts, which can be read separately. In the first part we study aspects of topological field theories. We show how to topologically twist three-dimensional N=2 supersymmetric Chern-Simons theory using a contact structure on the underlying manifold. This gives us a formulation of Chern-Simons theory together with a set of auxiliary fields and an odd symmetry. For Seifert manifolds, we show how to use this odd symmetry to localize the path integral of Chern-Simons theory. The formulation of three-dimensional Chern-Simons theory using a contact structure admits natural generalizations to higher dimensions. We introduce and study these theories. The focus is on the five-dimensional theory, which can be understood as a topologically twisted version of N=1 supersymmetric Yang-Mills theory. When formulated on contact manifolds that are circle fibrations over a symplectic manifold, it localizes to contact instantons. For the theory on the five-sphere, we show that the perturbative part of the partition function is given by a matrix model. In the second part of the thesis, we study supersymmetric sigma models in the Hamiltonian formalism, both in a classical and in a quantum mechanical setup. We argue that the so called Chiral de Rham complex, which is a sheaf of vertex algebras, is a natural framework to understand quantum aspects of supersymmetric sigma models in the Hamiltonian formalism. We show how a class of currents which generate symmetry algebras for the classical sigma model can be defined within the Chiral de Rham complex framework, and for a six-dimensional Calabi-Yau manifold we calculate the equal-time commutators between the currents and show that they generate the Odake algebra.

<p>The main topic of this doctoral thesis is D-branes in string theory, expressed in the language of conformal field theory. The purpose of string theory is to describe the elementary particles and the fundamental interactions of nature, including gravitation as a quantum theory. String theory has not yet reached the status to make falsifiable predictions, thus it is not certain that string theory has any direct relevance to physics. On the other hand, string theory related research has led to progress in mathematics.</p><p>We begin with a short introduction to conformal field theory and some of its applications to string theory. We also introduce vertex algebras and discuss their relevance to conformal field theory. Some classes of conformal field theories are introduced, and we discuss the relevant vertex algebras, as well as their interpretation in terms of string theory.</p><p>In string theory, a D-brane specifies where the endpoint of the string lives. Many aspects of string theory can be described in terms of a conformal field theory, which is a field theory that lives on a two-dimensional space. The conformal field theory counterpart of a D-brane is a boundary state, which in some cases has a natural interpretation as constraining the string end point. The main focus of this thesis is on the interpretation of boundary states in terms of D-branes in curved target spaces.</p>

The main topic of this doctoral thesis is D-branes in string theory, expressed in the language of conformal field theory. The purpose of string theory is to describe the elementary particles and the fundamental interactions of nature, including gravitation as a quantum theory. String theory has not yet reached the status to make falsifiable predictions, thus it is not certain that string theory has any direct relevance to physics. On the other hand, string theory related research has led to progress in mathematics. We begin with a short introduction to conformal field theory and some of its applications to string theory. We also introduce vertex algebras and discuss their relevance to conformal field theory. Some classes of conformal field theories are introduced, and we discuss the relevant vertex algebras, as well as their interpretation in terms of string theory. In string theory, a D-brane specifies where the endpoint of the string lives. Many aspects of string theory can be described in terms of a conformal field theory, which is a field theory that lives on a two-dimensional space. The conformal field theory counterpart of a D-brane is a boundary state, which in some cases has a natural interpretation as constraining the string end point. The main focus of this thesis is on the interpretation of boundary states in terms of D-branes in curved target spaces.

Cette these est composee de deux parties independantes ayant pour point commun l’utilisation intensive de la theorie des ∞-categories. Dans la premiere, on s’interesse aux liens entre deux approches differentes de la formalisation de la physique des particules : les algebres vertex et les algebres a factorisation a la Costello. On montre en particulier que dans le cas des theories dites topologiques, elles sont equivalentes. Plus precisement, on montre que les∞-categories de fibres vectoriels factorisant non-unitaires sur une variete algebrique complexe lisse X est equivalente a l’∞-categorie des EM-algebres non-unitaires et de dimension finie, ou M est la variete topologique associee a X. Dans la seconde, avec Mathieu Anel, nous etudions la caracterisation de l’exponentiabilite dans l’∞-categorie des ∞-topos. Nous montrons que les ∞-topos exponentiables sont ceux dont l’∞-categorie de faisceaux est continue. Une consequence notable est que l’∞-categorie des faisceaux en spectres sur un ∞-topos exponentiable est un objet dualisable de l’∞-categorie des ∞-categories cocompletes stables munie de son produit tensoriel. Ce chapitre contient aussi une construction des ∞-coends a partir de la theorie du produit tensoriel d’∞- categories cocompletes, ainsi qu’une description des ∞-categories de faisceaux sur un ∞-topos exponentiable en termes de faisceaux de Leray. / This thesis is made of two independent parts, both relying heavily on the theory of ∞-categories. In the first chapter, we approach two different ways to formalize modern particle physics, through the theory of vertex algebras and the theory of factorisation algebras a la Costello. We show in particular that in the case of ‘topological field theories’, they are equivalent. More precisely, we show that the ∞-category of non-unital factorization vector bundles on a smooth complex variety X is equivalent to the ∞-category of non-unital finite dimensional EM-algebras where M is the topological manifold associated to X. In the second one, with Mathieu Anel, we study a characterization of exponentiable objects of the∞-category of∞-toposes.We show that an ∞-topos is exponentiable if and only if its ∞-category of sheaves of spaces is continuous. An important consequence is the fact that the ∞-category of sheaves of spectra on an exponentiable ∞-topos is a dualisable object of the ∞-category of cocontinuous stable ∞-categories endowed with its usual tensor product. This chapter also includes a ix construction of∞-coends from the theory of tensor products of cocomplete∞- categories, together with a description of∞-categories of sheaves on exponentiable ∞-toposes in terms of Leray sheaves.

Motivados pelos resultados do artigo [BBFK11], nosso trabalho começa analisando, no caso da álgebra de Lie afim sl(n;C), a possibilidade de se obter módulos de Verma J-imaginários, via representações análogas às feitas por Cox em [Cox05]. Inicialmente consideramos, por simplicidade, n = 2 e, só então, analisamos o caso geral. Depois, de modo análogo, estudamos os artigos [CF04] e [CF05] com o intuito de obter módulos J-intermediários de Wakimoto. Finalmente imbutimos, no caso n = 2, uma ação de álgebra de Virasoro nos módulos imaginários de Wakimoto, utilizando-nos do resultado exposto em [EFK98], em que tal problema é abordado para o caso dos módulos de Verma. Desta forma, obtemos equações análogas às de Knizhnik-Zamolodchikov (equações KZ) para os módulos imaginários de Wakimoto. / Following the results of [BBFK11], our work starts analyzing (for bsl(n;C)) if we can obtain J-imaginary Verma modules using similar representations used by Cox in [Cox05]. We did it for n = 2 and after, for the general case. The next step was the study of J-intermediate Wakimoto modules, following the ideas of [CF04] and [CF05]. To finish, for affine sl(2;C), we defined an action of Virasoro algebra on the imaginary Wakimoto modules following [EFK98] and we obtained an analogue of the KZ-equations for imaginary Wakimoto modules.

Motivados pelos resultados do artigo [BBFK11], nosso trabalho começa analisando, no caso da álgebra de Lie afim sl(n;C), a possibilidade de se obter módulos de Verma J-imaginários, via representações análogas às feitas por Cox em [Cox05]. Inicialmente consideramos, por simplicidade, n = 2 e, só então, analisamos o caso geral. Depois, de modo análogo, estudamos os artigos [CF04] e [CF05] com o intuito de obter módulos J-intermediários de Wakimoto. Finalmente imbutimos, no caso n = 2, uma ação de álgebra de Virasoro nos módulos imaginários de Wakimoto, utilizando-nos do resultado exposto em [EFK98], em que tal problema é abordado para o caso dos módulos de Verma. Desta forma, obtemos equações análogas às de Knizhnik-Zamolodchikov (equações KZ) para os módulos imaginários de Wakimoto. / Following the results of [BBFK11], our work starts analyzing (for bsl(n;C)) if we can obtain J-imaginary Verma modules using similar representations used by Cox in [Cox05]. We did it for n = 2 and after, for the general case. The next step was the study of J-intermediate Wakimoto modules, following the ideas of [CF04] and [CF05]. To finish, for affine sl(2;C), we defined an action of Virasoro algebra on the imaginary Wakimoto modules following [EFK98] and we obtained an analogue of the KZ-equations for imaginary Wakimoto modules.