Thesis (doctoral)--Rheinische Friedrich-Wilhelms-Universität Bonn, 2004. / Includes bibliographical references (p. 87-89).

Graduation date: 1997

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Additional advisors: Nikolai Chernov, S. S. Ravindran, Alan Sprague, Min Sun. Description based on contents viewed Feb. 6, 2008; title from title screen. Includes bibliographical references.

One of the methods used for the construction of the classical Alexander horned sphere leads naturally to generalization to horned spheres of higher order. Let M2, denote the Alexander horned sphere. This is a 2-horned sphere of order 2. Denote by M 3 and M4, two 2-horned spheres of orders 3 and 4, respectively, constructed by such a generalization. The fundamental groups of the complements of M2, M3, and M4 are derived, and representations of these groups onto the Alternating Group, A5, are found. The form of the presentations of these fundamental groups leads to a more general class of groups, denoted by Gk, k ≥ 2. A set of homomorphisms ϴkl : Gk, k ≥ l ≥ 2 is found, which has a clear geometric meaning as applied to the groups G2, G3, and G4. Two theorems relating to direct systems of non-abelian groups are proved and applied to the groups Gk. The implication of these theorems is that the groups Gk, k≥2 are all free groups of countably infinite rank and that the embeddings of M2, M3, and M4 in E3 cannot be distinguished by means of fundamental groups. *33 pages)

This dissertation provides the first known examples of finite co-volume Kleinian groups which have co- final towers of finite index subgroups with positive rank gradient. We prove that if the fundamental group of an orientable finite volume hyperbolic 3-manifold has fi nite index in the reflection group of a right-angled ideal polyhedron in H^3 then it has a co-fi nal tower of fi nite sheeted covers with positive rank gradient. The manifolds we provide are also known to have co- final towers of covers with zero rank gradient. We also prove that the reflection groups of compact right-angled hyperbolic polyhedra satisfying mild conditions have co-fi nal towers of fi nite sheeted covers with positive rank gradient. / text

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.

Let F be a field finitely generated and of transcendence degree 2 over \(\bar{\mathbb{Q}}\). We describe a correspondence between the smooth algebraic surfaces X defined over \(\bar{\mathbb{Q}}\) with field of rational functions F and Florian Pop’s geometric sets of prime divisors on \(Gal(\bar{F}/F)\), which are purely group-theoretical objects. This allows us to give a strong anabelian theorem for these surfaces. As a corollary, for each number field K, we give a method to construct infinitely many profinite groups \(\Gamma\) such that \(Out_{cont} (\Gamma)\) is isomorphic to \(Gal(\bar{K}/K)\), and we find a host of new categories which answer the Question of Ihara/Conjecture of Oda-Matsumura. / Mathematics

The Selmer varieties of a hyperbolic curve X over ℚ are refinements of the Selmer group arising from replacing the Tate module of the Jacobian with higher quotients of the unipotent étale fundamental group. It is hoped that these refinements carry extra arithmetic information. In particular the nonabelian Chabauty method developed by Kim uses the Selmer variety to give a new method to find the set X(ℚ). This thesis studies certain local and global properties of the Selmer varieties associated to finite dimensional quotients of the unipotent fundamental group of a curve over ℚ. We develop new methods to prove finiteness of the intersection of the Selmer varieties with the set of local points (and hence of the set of rational points) and new methods to implement this explicitly, giving the first examples of explicit nonabelian Chabauty theory for rational points on projective curves.

Orientador: Dessislava Hristova Kochloukova / Dissertação (mestrado) - Universidade Estadual de Campinas. Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-04T11:05:09Z (GMT). No. of bitstreams: 1 Kitani_PatriciaMassae_M.pdf: 1013676 bytes, checksum: 794e7e67a9a90f759b790877a816b7f6 (MD5) Previous issue date: 2005 / Resumo: Este trabalho consistiu no estudo das aplicações de topologia algébrica (recobrimentos, teorema de Van Kampen) em teoria de grupos e também, no estudo detalhado do resultado de R. Bieri, R. Strebel [Proc. London Math. Soc. (3) 41 (1980), no. 3, 439¿464], que para um grupo G do tipo FP2, ou G contém subgrupo livre não cíclico ou para qualquer subgrupo normal N C G tal que Q = G/N é abeliano, N/[N,N] é um ZQ-módulo manso via conjugação. A definição de módulo manso usa o invariante de Bieri-Strebel §A(Q), nesse caso A = N/[N,N] / Abstract: This work consisted of the study of the applications of algebraic topology (covering maps, Van Kampen theorem) in group theory and also, in the detailed study of a result of R. Bieri, R. Strebel [Proc. London Math. Soc. (3) 41 (1980), no. 3, 439¿464], that for a group G of type FP2, either G has a free non-cyclic subgroup or for any normal subgroup N C G such that Q = G/N is abelian, N/[N,N] is a tame ZQ-module where Q acts via conjugation. The definition of tame module uses the Bieri-Strebel invariant §A(Q), in this case A = N/[N,N] / Mestrado / Algebra / Mestre em Matemática

Deux méthodes de construction de représentations de groupes sont présentées. La première propose une stratégie essayant de déterminer les représentations de groupes libres de type fini à valeurs dans tout réseau de groupes de Lie réel. La seconde, après avoir revu une construction d'une surface hyperbolique complexe, c'est-à-dire le quotient du plan hyperbolique complexe par un réseau, et examiné soigneusement ses propriétés, produit une infinité de représentations non-conjuguées, à valeurs dans un réseau du groupe des isométries du plan hyperbolique complexe, de groupes fondamentaux de variétés hyperboliques fermées de dimension 3, obtenues comme des fibrés en surfaces sur le cercle. / Two construction methods of group representations are presented. The first one proposes a strategy to try to determine the representations of finitely generated free groups into any lattice in real Lie groups. The second, after reviewing a construction of a complex hyperbolic surface, that is the quotient of the complex hyperbolic plane by a lattice, and examining its properties carefully, yields infinitely many non-conjugate representations into a lattice in the group of isometries of the complex hyperbolic plane, of fundamental groups of closed hyperbolic 3-dimensional manifolds, obtained as surface bundles over the circle.