REPRESENTATIONS of ELEMENTARY ABELIAN P-GROUPS and BUNDLES on GRASSMANNIANS
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Fusion Systems and Group Actions with Abelian Isotropy Subgroups
FUSION SYSTEMS AND GROUP ACTIONS WITH ABELIAN ISOTROPY SUBGROUPS OZG¨ UN¨ UNL¨ U¨ AND ERGUN¨ YALC¸IN Abstract. We prove that if a finite group G acts smoothly on a manifold M so that all the isotropy subgroups are abelian groups with rank ≤ k, then G acts freely and smoothly n1 n on M × S × · · · × S k for some positive integers n1; : : : ; nk. We construct these actions using a recursive method, introduced in an earlier paper, that involves abstract fusion systems on finite groups. As another application of this method, we prove that every finite solvable group acts freely and smoothly on some product of spheres with trivial action on homology. 1. Introduction and statement of results Madsen-Thomas-Wall [7] proved that a finite group G acts freely on a sphere if (i) G has no subgroup isomorphic to the elementary abelian group Z=p × Z=p for any prime number p and (ii) has no subgroup isomorphic to the dihedral group D2p of order 2p for any odd prime number p. At that time the necessity of these conditions were already known: P. A. Smith [12] proved that the condition (i) is necessary and Milnor [8] showed the necessity of the condition (ii). As a generalization of the above problem we are interested in the problem of character- izing those finite groups which can act freely and smoothly on a product of k spheres for a given positive integer k. In the case k = 1, Madsen-Thomas-Wall uses surgery theory and considers the unit spheres of linear representations of subgroups to show that certain surgery obstructions vanish. -
Finite Group Actions on the Four-Dimensional Sphere Finite Group Actions on the Four-Dimensional Sphere
Finite Group Actions on the Four-Dimensional Sphere Finite Group Actions on the Four-Dimensional Sphere By Sacha Breton, B.Sc. A Thesis Submitted to the School of Graduate Studies in Partial Fulfilment of the Requirements for the Degree of Master of Science McMaster University c Copyright by Sacha Breton, August 30th 2011 Master of Science (2011) McMaster University Hamilton, Ontario Department of Mathematics and Statistics TITLE: Finite Group Actions on the Four-Dimensional Sphere AUTHOR: Sacha Breton B.Sc. (McGill University) SUPERVISOR: Ian Hambleton NUMBER OF PAGES: 41 + v ii Abstract Smith theory provides powerful tools for understanding the geometry of singular sets of group actions on spheres. In this thesis, tools from Smith theory and spectral sequences are brought together to study the singular sets of elementary abelian groups acting locally linearly on S4. It is shown that the singular sets of such actions are homeomorphic to the singular sets of linear actions. A short review of the literature on group actions on S4 is included. iii Acknowledgements I would like to thank Professor Ian Hambleton for his suggestion of thesis topic, for the breadth and depth of his advice, and for his patience and encouragement. I would also like to thank Val´erieTremblay, Barnaby and Sue Ore, my parents, and my friends for their continued support. iv Contents Descriptive Note ii Abstract iii Acknowledgements iv 1 Introduction 1 2 Introductory Material 1 2.1 Basic definitions and conventions . .1 2.2 The Projection and the Transfer homomorphisms . .4 2.3 Smith Theory . .7 2.4 Group cohomology . -
ELEMENTARY ABELIAN P-SUBGROUPS of ALGEBRAIC GROUPS
ROBERT L. GRIESS, JR ELEMENTARY ABELIAN p-SUBGROUPS OF ALGEBRAIC GROUPS Dedicated to Jacques Tits for his sixtieth birthday ABSTRACT. Let ~ be an algebraically closed field and let G be a finite-dimensional algebraic group over N which is nearly simple, i.e. the connected component of the identity G O is perfect, C6(G °) = Z(G °) and G°/Z(G °) is simple. We classify maximal elementary abelian p-subgroups of G which consist of semisimple elements, i.e. for all primes p ~ char K. Call a group quasisimple if it is perfect and is simple modulo the center. Call a subset of an algebraic group total if it is in a toms; otherwise nontoral. For several quasisimple algebraic groups and p = 2, we define complexity, and give local criteria for whether an elementary abelian 2-subgroup of G is total. For all primes, we analyze the nontoral examples, include a classification of all the maximal elementary abelian p-groups, many of the nonmaximal ones, discuss their normalizers and fusion (i.e. how conjugacy classes of the ambient algebraic group meet the subgroup). For some cases, we give a very detailed discussion, e.g. p = 3 and G of type E6, E 7 and E 8. We explain how the presence of spin up and spin down elements influences the structure of projectively elementary abelian 2-groups in Spin(2n, C). Examples of an elementary abelian group which is nontoral in one algebraic group but toral in a larger one are noted. Two subsets of a maximal torus are conjugate in G iff they are conjugate in the normalizer of the torus; this observation, with our discussion of the nontoral cases, gives a detailed guide to the possibilities for the embedding of an elementary abelian p-group in G. -
The M\" Obius Number of the Socle of Any Group
Contents 1 Definitions and Statement of Main Result 2 2 Proof of Main Result 3 2.1 Complements ........................... 3 2.2 DirectProducts.......................... 5 2.3 The Homomorphic Images of a Product of Simple Groups . 6 2.4 The M¨obius Number of a Direct Power of an Abelian Simple Group ............................... 7 2.5 The M¨obius Number of a Direct Power of a Nonabelian Simple Group ............................... 8 2.6 ProofofTheorem1........................ 9 arXiv:1002.3503v1 [math.GR] 18 Feb 2010 1 The M¨obius Number of the Socle of any Group Kenneth M Monks Colorado State University February 18, 2010 1 Definitions and Statement of Main Result The incidence algebra of a poset P, written I (P ) , is the set of all real- valued functions on P × P that vanish for ordered pairs (x, y) with x 6≤ y. If P is finite, by appropriately labeling the rows and columns of a matrix with the elements of P , we can see the elements of I (P ) as upper-triangular matrices with zeroes in certain locations. One can prove I (P ) is a subalgebra of the matrix algebra (see for example [6]). Notice a function f ∈ I(P ) is invertible if and only if f (x, x) is nonzero for all x ∈ P , since then we have a corresponding matrix of full rank. A natural function to consider that satisfies this property is the incidence function ζP , the characteristic function of the relation ≤P . Clearly ζP is invertible by the above criterion, since x ≤ x for all x ∈ P . We define the M¨obius function µP to be the multiplicative inverse of ζP in I (P ) . -
Arxiv:1310.6548V1 [Math.GR] 24 Oct 2013 Every Hwta H Iuto O Ocmatmnflsi Ut Di Quite Is 3
FINITE SUBGROUPS OF DIFFEOMORPHISM GROUPS ∗ VLADIMIR L. POPOV Abstract. We prove (1) the existence of a noncompact smooth four-di- mensional manifold M such that Diff(M) contains an isomorphic copy of every finitely presented group; (2) a finiteness theorem on finite simple subgroups of Diff(N) for compact manifolds N. 1. In [Po10, Sect. 2] was introduced the definition of abstract Jordan group and initiated exploration of the following two problems on automorphism groups and birational self-map groups of algebraic varieties: Problem A. Describe algebraic varieties X for which Aut(X) is Jordan. Problem B. The same with Aut(X) replaced by Bir(X). Recall from [Po10, Def. 2.1] that Jordaness of a group is defined as follows: Definition 1. A group G is called a Jordan group if there exists a positive integer dG, depending on G only, such that every finite subgroup F of G contains a normal abelian subgroup whose index in F is at most dG. Informally Jordaness means that all finite subgroups of G are “almost” abelian in the sense that they are extensions of abelian groups by finite groups taken from a finite list. Since the time of launching the exploration program of Problems A and B a rather extensive information on them has been obtained (see [Po132]), but, for instance, at this writing (October 2013) is still unknown whether there exists X with non-Jordan group Aut(X) (see Question 1 in [Po132]; it is interesting to juxtapose it with Corollary 2 below). 2. In this note we explore the counterpart of Problem A, in which algebraic varieties X are replaced by connected smooth topological manifolds M, and arXiv:1310.6548v1 [math.GR] 24 Oct 2013 Aut(X) is replaced by Diff(M), the diffeomorphism group of M. -
The Theory of Finite Groups: an Introduction (Universitext)
Universitext Editorial Board (North America): S. Axler F.W. Gehring K.A. Ribet Springer New York Berlin Heidelberg Hong Kong London Milan Paris Tokyo This page intentionally left blank Hans Kurzweil Bernd Stellmacher The Theory of Finite Groups An Introduction Hans Kurzweil Bernd Stellmacher Institute of Mathematics Mathematiches Seminar Kiel University of Erlangen-Nuremburg Christian-Albrechts-Universität 1 Bismarckstrasse 1 /2 Ludewig-Meyn Strasse 4 Erlangen 91054 Kiel D-24098 Germany Germany [email protected] [email protected] Editorial Board (North America): S. Axler F.W. Gehring Mathematics Department Mathematics Department San Francisco State University East Hall San Francisco, CA 94132 University of Michigan USA Ann Arbor, MI 48109-1109 [email protected] USA [email protected] K.A. Ribet Mathematics Department University of California, Berkeley Berkeley, CA 94720-3840 USA [email protected] Mathematics Subject Classification (2000): 20-01, 20DXX Library of Congress Cataloging-in-Publication Data Kurzweil, Hans, 1942– The theory of finite groups: an introduction / Hans Kurzweil, Bernd Stellmacher. p. cm. — (Universitext) Includes bibliographical references and index. ISBN 0-387-40510-0 (alk. paper) 1. Finite groups. I. Stellmacher, B. (Bernd) II. Title. QA177.K87 2004 512´.2—dc21 2003054313 ISBN 0-387-40510-0 Printed on acid-free paper. © 2004 Springer-Verlag New York, Inc. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. -
Kernels of Linear Representations of Lie Groups, Locally Compact
Kernels of Linear Representations of Lie Groups, Locally Compact Groups, and Pro-Lie Groups Markus Stroppel Abstract For a topological group G the intersection KOR(G) of all kernels of ordinary rep- resentations is studied. We show that KOR(G) is contained in the center of G if G is a connected pro-Lie group. The class KOR(C) is determined explicitly if C is the class CONNLIE of connected Lie groups or the class ALMCONNLIE of almost con- nected Lie groups: in both cases, it consists of all compactly generated abelian Lie groups. Every compact abelian group and every connected abelian pro-Lie group occurs as KOR(G) for some connected pro-Lie group G. However, the dimension of KOR(G) is bounded by the cardinality of the continuum if G is locally compact and connected. Examples are given to show that KOR(C) becomes complicated if C contains groups with infinitely many connected components. 1 The questions we consider and the answers that we have found In the present paper we study (Hausdorff) topological groups. Ifall else fails, we endow a group with the discrete topology. For any group G one tries, traditionally, to understand the group by means of rep- resentations as groups of matrices. To this end, one studies the continuous homomor- phisms from G to GLnC for suitable positive integers n; so-called ordinary representa- tions. This approach works perfectly for finite groups because any such group has a faithful ordinary representation but we may face difficulties for infinite groups; there do exist groups admitting no ordinary representations apart from the trivial (constant) one. -
On 2-Closures of Rank 3 Groups
On 2-closures of rank 3 groups S.V. Skresanov∗ Abstract A permutation group G on Ω is called a rank 3 group if it has pre- cisely three orbits in its induced action on Ω×Ω. The largest permutation group on Ω having the same orbits as G on Ω × Ω is called the 2-closure of G. A description of 2-closures of rank 3 groups is given. As a spe- cial case, it is proved that 2-closure of a primitive one-dimensional affine rank 3 permutation group of sufficiently large degree is also affine and one-dimensional. 1 Introduction Let G be a permutation group on a finite set Ω. Recall that the rank of G is the number of orbits in the induced action of G on Ω Ω; these orbits are called 2-orbits. If a rank 3 group has even order, then its non-diagonal× 2-orbit induces a strongly regular graph on Ω, which is called a rank 3 graph. It is readily seen that a rank 3 group acts on the corresponding rank 3 graph as an automorphism group. Notice that an arc-transitive strongly regular graph need not be a rank 3 graph, since its automorphism group might be intransitive on non-arcs. Related to this is the notion of a 2-closure of a permutation group. The group G(2) is the 2-closure of a permutation group G, if G(2) is the largest permutation group having the same 2-orbits as G. Clearly G G(2), the 2-closure of G(2) is again G(2), and G(2) has the same rank as G. -
Notes on Finite Group Theory
Notes on finite group theory Peter J. Cameron October 2013 2 Preface Group theory is a central part of modern mathematics. Its origins lie in geome- try (where groups describe in a very detailed way the symmetries of geometric objects) and in the theory of polynomial equations (developed by Galois, who showed how to associate a finite group with any polynomial equation in such a way that the structure of the group encodes information about the process of solv- ing the equation). These notes are based on a Masters course I gave at Queen Mary, University of London. Of the two lecturers who preceded me, one had concentrated on finite soluble groups, the other on finite simple groups; I have tried to steer a middle course, while keeping finite groups as the focus. The notes do not in any sense form a textbook, even on finite group theory. Finite group theory has been enormously changed in the last few decades by the immense Classification of Finite Simple Groups. The most important structure theorem for finite groups is the Jordan–Holder¨ Theorem, which shows that any finite group is built up from finite simple groups. If the finite simple groups are the building blocks of finite group theory, then extension theory is the mortar that holds them together, so I have covered both of these topics in some detail: examples of simple groups are given (alternating groups and projective special linear groups), and extension theory (via factor sets) is developed for extensions of abelian groups. In a Masters course, it is not possible to assume that all the students have reached any given level of proficiency at group theory. -
Annihilator$Small Right Ideals
ANNIHILATOR-SMALL RIGHT IDEALS W.K. Nicholson Yiqiang Zhou Department of Mathematics Department of Mathematics University of Calgary Memorial University of Newfoundland Calgary T2N 1N4, Canada St. John’sA1C 5S7, Canada [email protected] [email protected] April 22, 2008 Abstract A right ideal A of a ring R is called annihilator-small if A + T = R; T a right ideal, implies that l(T ) = 0; where l() indicates the left annihilator. The sum Ar of all such right ideals turns out to be a two-sided ideal that contains the Jacobson radical and the left singular ideal, and is contained in the ideal generated by the total of the ring. The ideal Ar is studied, conditions when it is annihilator small are given, its relationship to the total of the ring is examined, and its connection with related rings is investigated. Keywords: Small right ideals, annihilators, total of a ring Mathematics Subject Classi…cation (2000): 16A34, 16A21, 16D25 1. Introduction It is well known that if a; b are elements of a ring R; then 1 ab is a unit if and only if 1 ba is a unit. The starting point in this paper is that the analogue for left annihilators is also true: l(1 ab) = 0 if and only if l(1 ba) = 0: This leads to the concept of an “annihilator-small” right ideal. In fact, the set Kr of all elements k such that kR is annihilator small turns out to be a semi-ideal that contains both the Jacobson radical and the left singular ideal and is contained in the total of the ring. -
Primitive Idempotents and the Socle in Group Rings of Periodic Abelian Groups Compositio Mathematica, Tome 32, No 2 (1976), P
COMPOSITIO MATHEMATICA J. S. RICHARDSON Primitive idempotents and the socle in group rings of periodic abelian groups Compositio Mathematica, tome 32, no 2 (1976), p. 203-223 <http://www.numdam.org/item?id=CM_1976__32_2_203_0> © Foundation Compositio Mathematica, 1976, tous droits réservés. L’accès aux archives de la revue « Compositio Mathematica » (http: //http://www.compositio.nl/) implique l’accord avec les conditions géné- rales d’utilisation (http://www.numdam.org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d’une infrac- tion pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/ COMPOSITIO MATHEMATICA, Vol. 32, Fasc. 2, 1976, pag. 203-223 Noordhoff International Publishing Printed in the Netherlands PRIMITIVE IDEMPOTENTS AND THE SOCLE IN GROUP RINGS OF PERIODIC ABELIAN GROUPS J. S. Richardson Abstract Let K be a field and G a periodic abelian group containing no elements of order p if char K = p > 0. We establish necessary and sufficient conditions for the group ring KG to contain primitive idempotents. We also characterize the socle of KG, and show that when the socle is non-zero the ascending socular series reaches KG after a finite number of steps. 1. Introduction Let K be a field and G a periodic abelian group containing no elements of order p if char K = p > 0. We shall investigate the circumstances under which the group ring KG contains primitive idempotents. We find (Lemma 3.1 and Theorem 3.4) that the following three conditions are necessary and sufficient: (a) G is almost locally cyclic (i.e. -
Cyclotomy and Difference Families in Elementary Abelian Groups*
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector JOURNAL OF NUMBER THEORY 4, 17-47 (1972) Cyclotomy and Difference Families in Elementary Abelian Groups* RICHARD M. WILSON+ Department of Mathematics, Ohio State University, Columbus, Ohio 43210 Communicated by A. C. Woods Received May 1, 1970 By a (v, k, h)-difference family in an additive abelian group G of order v, we mean a family (4 j i E Z) of subsets of G, each of cardinality k, and such that among the differences (a - b / q b E Z3<; a # b; i E Z) each nonzero g E G occurs X times. The existence of such a difference family implies the existence of a (v, k, X)-BIBD with G as a regular group of automorphisms. The multiplicative structure of finite fields is used here to construct difference families in their additive groups. It is proven that if q is a prime power and q > {ik(k - l)}klk-l), then there exists a (q, k, h)-difference family in the elementary abelian group of order q iff X(q - 1) = 0 (mod k(k - 1)). Some extensions of known con- structions and partially balanced designs are also discussed. 1. BALANCED INCOMPLETE BLOCK DESIGNS An incidence structure is a triple (P, L, 9) where P is a set of points, L is a set of lines, and Y is an incidence relation between P and L which we view as a mapping from P x L into the set of integers (0, I}.