Wir berechnen L²-Invarianten bestimmter nichtuniformer Gitter in halbeinfachen Lie-Gruppen mithilfe der Borel-Serre-Kompaktifizierung arithmetisch definierter lokalsymmetrischer Räume. Als Hauptergebnisse erhalten wir neue Abschätzungen für Novikov-Shubin-Zahlen und das Verschwinden der L²-Torsion für Gitter in Gruppen mit geradem Fundamentalrang. Wir diskutieren Anwendungen auf Gromovs Null-im-Spektrum-Vermutung sowie auf eine Proportionalitätsvermutung für die L²-Torsion maßäquivalenter Gruppen. Im Schlussteil der Arbeit beschreiben wir einen Anpassungsvorgang für Chevalley-Basen komplexer halbeinfacher Lie-Algebren. Zu einer gegebenen Realform liefert dieser eine Basis mit halb- und ganzzahligen Strukturkonstanten, die wir durch das Wurzelsystem mit Involution ausdrücken.

In this thesis we explore various aspects of Calabi-Yau (CY) manifolds and com- pactifications of the heterotic string over them. At first we focus on classifying symmetries and computing Hodge numbers of smooth CY quotients. Being non- simply connected, these quotients are an integral part of CY compactifications of the heterotic string, aimed at producing realistic string vacua. Discrete symmetries of such spaces that are generically present in the moduli space, are phenomenologically important since they may appear as symmetries of the associated low energy theory. We classify such symmetries for the class of smooth Complete Intersection CY (CICY) quotients, resulting in a large number of regular and R-symmetry examples. Our results strongly suggest that generic, non-freely acting symmetries for CY quotients arise relatively frequently. A large number of string derived Standard Models (SM) were recently obtained over this class of CY manifolds indicating that our results could be phenomenologically important. We also specialise to certain loci in the moduli space of a quintic quotient to produce highly symmetric CY quotients. Our computations thus far are the first steps towards constructing a sizeable class of highly symmetric smooth CY quotients. Knowledge of the topological properties of the internal space is vital in determining the suitability of the space for realistic string compactifications. Employing the tools of polynomial deformation and counting of invariant Kähler classes, we compute the Hodge numbers of a large number of smooth CICY quotients. These were later verified by independent cohomology computations. We go on to develop the machinery to understand the geometry of CY manifolds embedded as hypersurfaces in a product of del Pezzo surfaces. This led to an interesting account of the quotient space geometry, enabling the computation of Hodge numbers of such CY quotients. Until recently only a handful of CY compactifications were known that yielded low energy theories with desirable MSSM features. The recent construction of rank 5 line bundle sums over smooth CY quotients has led to several SU(5) GUTs with the exact MSSM spectrum. We derive semi-analytic results on the finiteness of the number of such line bundle models, and study the relationship between the volume of the CY and the number of line bundle models over them. We also imply a possible correlation between the observed number of generations and the value of the gauge coupling constants of the corresponding GUTs. String compactifications with underlying SO(10) GUTs are theoretically attractive especially since the discovery that neutrinos have non-zero mass. With this in mind, we construct tens of thousands of rank 4 stable line bundle sums over smooth CY quotients leading to SO(10) GUTs.

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Neste trabalho estudaremos alguns resultados propostos por Benoit Kloe kner [Kl2] em sua tese de doutorado. Apresentamos prin ipalmente a prova da não-existência de compactificações diferenciáveis de Hadamard em espaços simétri os de tipo não- ompa to de posto k ≥ 2. / In this dissertation we will study some results proposed by Benoit Kloe kner [Kl2] in his do toral thesis. We mainly present the proof of non-existen e of diferentiable Hadamard compactific ations in symmetric spaces of non compact type of rank ≥ 2.

Neste trabalho estudaremos alguns resultados propostos por Benoit Kloe kner [Kl2] em sua tese de doutorado. Apresentamos prin ipalmente a prova da não-existência de compactificações diferenciáveis de Hadamard em espaços simétri os de tipo não- ompa to de posto k ≥ 2. / In this dissertation we will study some results proposed by Benoit Kloe kner [Kl2] in his do toral thesis. We mainly present the proof of non-existen e of diferentiable Hadamard compactific ations in symmetric spaces of non compact type of rank ≥ 2.

Orientador: Luiz Antonio Barrera San Martin / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-11T09:58:09Z (GMT). No. of bitstreams: 1 Souza_JosineyAlvesde_D.pdf: 1777083 bytes, checksum: 43943f3a9ea228d0eb5fbe6c6906cd93 (MD5) Previous issue date: 2008 / Resumo: Um semigrupo de transformação consiste de um semigrupo de aplicações contínuas definidas num espaço topológico. A hipótese sobre o semigrupo é a propriedade de reversibilidade, isto é, que a coleção das translações do semigrupo satisfaz a propriedade de intersecção finita. A idéia central é de dinamizar um semigrupo de transformação, sendo isto realizado pela introdução dos correspondentes objetos dinâmicos elementares da teoria de semifluxos, ou seja, os conjuntos limites, atratores e repulsores. O conceito de recorrência por cadeias é abordado de uma forma generalizada, sobre espaços paracompactos, tendo como fundamento certas famílias especiais de coberturas abertas do espaço base chamadas famílias admissíveis. Estudamos também ações de grupos de homeomorfismos sobre espaços compactos. Neste caso, a hipótese sobre o grupo é que ele seja gerado por um subsemigrupo reversível, a partir do qual são definidos todos os objetos dinâmicos elementares. Estudamos dois casos específicos de semigrupos de transformações. No primeiro caso, abordamos semigrupos de transformações em fibrados topológicos, especialmente em fibrados flag, e enfatizamos o estudo sobre transitividade por cadeias fibra a fibra. No segundo caso, estudamos ações de grupos sobre compactificações de Ellis, onde apresentamos uma relação entre o conceito de subsemigrupo semitotal e a transitividade por cadeias. Por último, introduzimos o conceito de função recorrente por cadeias, generalizando o conceito de função recorrente. / Abstract: Transformation semigroups are actions of semigroups of continuous maps on topological spaces. We consider reversible semigroups and study dynamics behaviors by introducing the elementary dynamic objects, originals of the semiflows theory, that is, the limit sets, attractors and repellers. We present the concept of chain recurrence for admissible families on paracompact spaces. We also study homeomorphism group action on compact spaces. In this case, the hypothesis on the group is the Ore's condictions. The elementary dynamics objects are defined from the action of the generator reversible subsemigroup. Then we study two specific cases of transformation semigroups. In the first case, we present results on the actions of endomorphism in flag bundles by emphasizing the chain transitivity in the fibres. Next, we study group actions in Ellis compactifications and relate the concept of semitotal subsemigroup to the chain transitivity. Finally, we introduce the concept of chain recurrent function and generalize the concept of recurrent function. / Doutorado / Geometria / Doutor em Matemática

Thesis advisor: Maksym Fedorchuk / A general smooth curve of genus six lies on a quintic del Pezzo surface. In [AK11], Artebani and Kondō construct a birational period map for genus six curves by taking ramified double covers of del Pezzo surfaces. The map is not defined for special genus six curves. In this dissertation, we construct a smooth Deligne-Mumford stack P₀ parametrizing certain stable surface-curve pairs which essentially resolves this map. Moreover, we give an explicit description of pairs in P₀ containing special curves. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Mathematics.

The nature of this paper is expository. The purpose is to present the fundamental material concerning actions of infinite discrete groups on the n-sphere and pseudo-Riemannian space forms based on the works of Gehring, Martin and Kulkarni and provide appropriate examples. Actions on the n-sphere split it into ordinary and limit sets. Assuming, additionally, that a group acting on the n-sphere has a certain convergence property, this thesis includes conditions for the existence of a homeomorphism between the limit set and the set of Freudenthal ends, as well as topological and quasiconformal conjugacy between convergence and Mobius groups. Since the certain pseudo-Riemannian space forms are diffeomorphic to non-compact spaces, the work of Hambleton and Pedersen gives conditions for the extension of discrete co-compact group actions on pseudo-Riemannian space forms to actions on the sphere. An example of such an extension is described. / Thesis / Master of Science (MSc)

This thesis is devoted to a study of applications of gauged linear sigma models. First, by constructing (0,2) analogues of Hori-Vafa mirrors, we have given and checked proposals for (0,2) mirrors to projective spaces, toric del Pezzo and Hirzebruch surfaces with tangent bundle deformations, checking not only correlation functions but also e.g. that mirrors to del Pezzos are related by blowdowns in the fashion one would expect. Also, we applied the recent proposal for mirrors of non-Abelian (2,2) supersymmetric two-dimensional gauge theories to examples of two-dimensional A-twisted gauge theories with exceptional gauge groups G_2 and E_8. We explicitly computed the proposed mirror Landau-Ginzburg orbifold and derived the Coulomb ring relations (the analogue of quantum cohomology ring relations). We also studied pure gauge theories, and provided evidence (at the level of these topologicalfield-theory-type computations) that each pure gauge theory (with simply-connected gauge group) flows in the IR to a free theory of as many twisted chiral multiplets as the rank of the gauge group. Last, we have constructed hybrid Landau-Ginzburg models that RG flow to a new family of non-compact Calabi-Yau threefolds, constructed as fiber products of genus g curves and noncompact Kahler threefolds. We only considered curves given as branched double covers of P^1. Our construction utilizes nonperturbative constructions of the genus g curves, and so provides a new set of exotic UV theories that should RG flow to sigma models on Calabi-Yau manifolds, in which the Calabi-Yau is not realized simply as the critical locus of a superpotential. / Doctor of Philosophy / This thesis is devoted to a study of vacua of supersymmetric string theory (superstring theory) by gauged linear sigma models. String theory is best known as the candidate to unify Einstein’s general relativity and quantum field theory. We are interested in theories with a symmetry exchanging bosons and fermions, known as supersymmetry. The study of superstring vacua makes it possible to connect string theory to the real world, and describe the Standard model as a low energy effective theory. Gauged linear sigma models are one of the most successful models to study superstring vacua by, for example, providing insights into the global structure of their moduli spaces. We will use gauged linear sigma models to study mirror symmetry and its heterotic generalization “(0, 2) mirror symmetry.” They are both world-sheet dualities relating different interpretations of the same (internal) superstring vacua. Mirror symmetry is a very powerful duality which exchanges classical and quantum effects. By studying mirror symmetry and (0, 2) mirror symmetry, we gain more knowledge of the properties of superstring vacua.

Si G est . un groupe localement compact, est-ce que chaque dérivation de LI (G) à M( G) est interne? Victor Losert dans [10] a démontré que la réponse est positive. Le but d'écrire ce mémoire est raconter son preuve en détail.