Advantages of the double coset enumeration technique include its use to represent group elements in a convenient shorter form than their usual permutation representations and to find nice permutation representations for groups. In this thesis we construct, by hand, several groups, including U₃(3) : 2, L₂(13), PGL₂(11), and PGL₂(7), represent their elements in the short form (symmetric representation) and produce their permutation representations.

Este projeto de mestrado tem por objetivo dar uma prova elementar do seguinte teorema de Tits, conhecido como Teorema da Alternativa de Tits: Seja G um grupo linear finitamente gerado sobre um corpo. Então G é solúvel por finito ou G contém um grupo livre não cíclico. Este teorema, que foi provado por J. Tits em 1972 [4], foi considerado pelo matemático J.P. Serre como um dos mais importantes resultados de álgebra do século XX. Quando dizemos uma prova elementar, não queremos absolutamente te dizer uma prova simples. Seguiremos a prova simplificada de John D. Dixon / This masters project aims to give an elementary proof of the following theorem of Tits, known as the Alternative Tits Theorem: Let G be a finitely generated linear group over a field. Then either G is solvable by finite or G contains a noncyclic free subgroup. This theorem was proved by J. Tits in 1972 [4], was considered by the mathematician J.P. Serre, as one of the most important algebra results of the XX century. When we say an elementary proof, we absolutely not mean a simple proof. We will follow the simplified proof of John D. Dixon

We establish several new results about the ( n )-solvable filtration, [Special characters omitted.] , of the string link concordance group [Special characters omitted.] . We first establish a relationship between ( n )-solvability of a link and its Milnor's μ-invariants. We study the effects of the Bing doubling operator on ( n )-solvability. Using this results, we show that the "other half" of the filtration, namely [Special characters omitted.] , is nontrivial and contains an infinite cyclic subgroup for links with sufficiently many components. We will also show that links modulo (1)-solvability is a nonabelian group. Lastly, we prove that the Grope filtration, [Special characters omitted.] of [Special characters omitted.] is not the same as the ( n )-solvable filtration.

The n-solvable filtration of the link concordance group, defined by Cochran, Orr, and Teichner in 2003, is a tool for studying smooth knot and link concordance that yields important results in low-dimensional topology. We focus on the first two stages of the n-solvable filtration, which are the class of 0-solvable links and the class of 0.5-solvable links. We introduce a new equivalence relation on links called 0-solve equivalence and establish both an algebraic and a geometric characterization 0-solve equivalent links. As a result, we completely characterize 0-solvable links and we give a classification of links up to 0-solve equivalence. We relate 0-solvable links to known results about links bounding gropes and Whitney towers in the 4-ball. We then establish a sufficient condition for a link to be 0.5-solvable and show that 0.5-solvable links must have vanishing Sato-Levine invariants.

Let G be a finite group and A be a subgroup of Aut(G). In this work, we studied the influence of the index of fixed point subgroup of A in G on the structure of G. When A is cyclic, we proved the following: (1) [G,A] is solvable if this index is squarefree and the orders of G and A are coprime. (2) G is solvable if the index of the centralizer of each x in H-G is squarefree where H denotes the semidirect product of G by A. Moreover, for an arbitrary subgroup A of Aut(G) whose order is coprime to the order of G, we showed that when G is solvable, then the Fitting length f([G,A]) of [G,A] is bounded above by the number of primes (counted with multiplicities) dividing the index of fixed point subgroup of A in G and this bound is best possible.

Groebner-Shirshov bases, introduced independently by Shirshov in 1962 and Buchberger in 1965, are powerful computational tools in mathematics, science, engineering, and computer science. This thesis focuses on the theories, algorithms, and applications of Groebner-Shirshov bases for two classes of noncommutative algebras: differential difference algebras and skew solvable polynomial rings. This thesis consists of three manuscripts (Chapters 2--4), an introductory chapter (Chapter 1) and a concluding chapter (Chapter 5). In Chapter 1, we introduce the background and the goals of the thesis. In Chapter 2, we investigate the Gelfand-Kirillov dimension of differential difference algebras. We find lower and upper bounds of the Gelfand-Kirillov dimension of a differential difference algebra under some conditions. We also give examples to demonstrate that our bounds are sharp. In Chapter 3, we generalize the Groebner-Shirshov basis theory to differential difference algebras with respect to any left admissible ordering and develop the Groebner-Shirshov basis theory of finitely generated free modules over differential difference algebras. By using the theory we develop, we present an algorithm to compute the Gelfand-Kirillov dimensions of finitely generated modules over differential difference algebras. In Chapter 4, we first define skew solvable polynomial rings, which are generalizations of solvable polynomial algebras and (skew) PBW extensions. Then we present a signature-based algorithm for computing Groebner-Shirshov bases in skew solvable polynomial rings over fields. Our algorithm can detect redundant reductions and therefore it is more efficient than the traditional Buchberger algorithm. Finally, in Chapter 5, we summarize our results and propose possible future work.

This Ph.D. thesis in mathematical physics concerns systems of interacting fermions with strong correlations. For these systems the physical properties can only be described in terms of the collective behavior of the fermions. Moreover, they are often characterized by a close competition between fermion localization versus delocalization, which can result in complex and exotic physical phenomena. Strongly correlated fermion systems are usually modelled by many-body Hamiltonians for which the kinetic- and interaction energy have the same order of magnitude. This makes them challenging to study as the application of conventional computational methods, like mean field- or perturbation theory, often gives unreliable results. Of particular interest are Hubbard-type models, which provide minimal descriptions of strongly correlated fermions. The research of this thesis focuses on such models defined on two-dimensional square lattices. One motivation for this is the so-called high-Tc problem of the cuprate superconductors. A main hypothesis is that there exists an underlying Fermi surface with nearly flat parts, i.e. regions where the surface is straight. It is shown that a particular continuum limit of the lattice system leads to an effective model amenable to computations. This limit is partial in that it only involves fermion degrees of freedom near the flat parts. The result is an effective quantum field theory that is analyzed using constructive bosonization methods. Various exactly solvable models of interacting fermions in two spatial dimensions are also derived and studied. / QC 20111207

Thesis (M.A.)--State University of New York at Binghamton, Department of Mathematical Sciences, 2009. / Includes bibliographical references.

Soit G un groupe de Lie résoluble connexe et H un de ses sous-groupes fermés connexes d'algèbres de Lie g et h respectivement. On note g* (resp. h*) le dual linéaire de g (resp. h) ). Le sujet de ma thèse consiste à étudier la restriction d'une série discrète π de G, associée à une orbite coadjointe Ω C g*, à H. Si la restriction de π à H se décompose en somme directe de représentations de H avec multiplicités finies, on dit que π est H-admissible. Notons Pg,n : Ω → h* l'application restriction. Il s'agit de démontrer la conjecture suivante due à Michel Duflo : 1. La représentation π est H-admissible si et seulement si l'application moment Pg,n est propre sur l'image. 2. Si π est H-admissible, et si T est une série discrète de H alors sa multiplicité dans la restriction de π à H doit pouvoir se calculer en « quantifiant » l'espace réduit correspondant (qui est compact dans ce cas). Dans cette thèse, nous apportons une réponse positive à cette conjecture dans deux situations, à savoir :(i) Le groupe G est résoluble exponentiel. (ii) Le groupe G est le produit semi direct d'un tore compact par le groupe de Heisenberg et H est un sous-groupe algébrique connexe. / Let G be a connected solvable Lie group and H a closed connected subgroup with Lie algebra g and h respectively. We denote g* (resp. h*) the dual of g (resp. h). The aim of my thesis is to study the restriction of a discrete series π of G, associated with a coadjoint orbit Ω C g* to H. If the restriction of π to H can be decomposed in to a direct sum of representations of H with finite multiplicities, we say that π is H-admissible. Let Pg,n : Ω → h* denote the restriction map. My objective is to show the following conjecture due to Michel Duflo : 1. The representation π i s H-admissible if and only if the moment application Pg,n is proper on the image. 2. If π is H-admissible, and if T is a discrete series of H then it s multiplicity in the restriction of π to H must be calculated by « quantifying » the corresponding reduced space (that is compact in this case). In this thesis, we provide a positive response to this conjecture in two situations, namely when: (i) G is exponential solvable Lie group. (ii) G is the semi direct product of a compact torus and the Heisenberg group and H is a connected algebraic subgroup.

Orientador: Luiz Antonio Barrera San Martin / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-10T11:48:47Z (GMT). No. of bitstreams: 1 Santos_EdsonCarlosLicurgo_D.pdf: 405695 bytes, checksum: 334d5172d85f7bc35539dbd900fbef67 (MD5) Previous issue date: 2007 / Resumo: Seja (g; [·,·]) uma álgebra de Lie com uma estrutura complexa integrável J. Os ± i-auto-espaços de J são subálgebras complexas de gC isomorfas a álgebra (g; [*]J ) com colchete [X * Y ]J = ½ ([X, Y ] - [JX, JY ]). Consideramos, no capítulo 2, o caso onde estas subálgebras são nilpotentes e mostramos que a álgebra de Lie original (g, [·,·]) é solúvel. Consideramos também o caso 6-dimensional e determinamos explicitamente a única álgebra de Lie possível (g; [*]J ). Finalizamos esse capítulo pruduzindo vários exemplos ilustrando diferentes situações, em particular mostramos que para cada s existe g com estrutura complexa J tal que (g; [*]J ) é s-passos nilpotente. Exemplos similares para estruturas hipercomplexas são também construidos. No capítulo 3 consideramos o caso onde os ±i-auto-espaços de J são subálgebras complexas solúveis e a álgebra complexa é uma álgebra de Lie semi-simples. Mostramos que, se a álgebra real é compacta, uma tal estrutura complexa depende unicamente de um subespaço da subálgebra de Cartan. Finalizamos esse capítulo considerando o caso em que as subálgebras solúveis complexas estão contidas em subálgebras de Borel de uma órbita aberta da ação dos automorfismos internos da álgebra real. Mostramos que, assim como no caso compacto, as estruturas complexas são determinandas, de modo único, por subespaços da subálgebra de Cartan. Ao final da tese apresentamos um procedimento, elaborado em MAPLE, que possibilita testar a identidade de Jacobi quando os colchetes de Lie são dados pelas constantes de estrutura / Abstract: Let (g; [·,·]) be a Lie algebra with an integrable complex structure J. The ±i eigenspaces of J are complex subalgebras of gC isomorphic to the algebra (g; [*]J )with bracket [X * Y ]J = ½ ([X, Y ] - [JX, JY ]). We consider, in chapter three, thecase where these subalgebras are nilpotent and prove that the original Lie algebra(g, [·,·]) must be solvable. We consider also the 6-dimensional case and determineexplicitly the possible nilpotent Lie algebras (g; [*]J ). We finish this chapter byproducing several examples illustrating different situations, in particular we showthat for each given s there exists g with complex structure J such that (g; [*]J ) iss-step nilpotent. Similar examples of hypercomplex structures are also built.In Chapter 3 we consider the case where the ± i eigenspaces of J are solvablecomplex subalgebras and gC is a semisimple Lie algebra. We prove that, if g is compact, such a complex structure comes from a subspace of the Cartan subalgebra.We finish this chapter by considering the case where the solvable complex subalgebras are contained in Borel subalgebras of an open orbit of the action of inner automorphisms of the real algebra.At the end of the thesis we present an algorithm, made in MAPLE, that allowus to verify the Jacobi identity when the Lie brackets are defined by the structureconstants / Doutorado / Mestre em Matemática