Random Generation of Finite and Profinite Groups and Group
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The Homology of Peiffer Products of Groups
New York Journal of Mathematics New York J. Math. 6 (2000) 55–71. The Homology of Peiffer Products of Groups W. A. Bogley and N. D. Gilbert Abstract. The Peiffer product of groups first arose in work of J.H.C. White- head on the structure of relative homotopy groups, and is closely related to problems of asphericity for two-complexes. We develop algebraic methods for computing the second integral homology of a Peiffer product. We show that a Peiffer product of superperfect groups is superperfect, and determine when a Peiffer product of cyclic groups has trivial second homology. We also introduce a double wreath product as a Peiffer product. Contents Introduction 55 1. The low-dimensional homology of products of subgroups 57 2. Twisted bilinear relations 60 3. The structure of SG∗H 61 4. Computations 63 References 70 Introduction Given two groups acting on each other by automorphisms, it is natural to ask whether these groups can be embedded in an overgroup in such a way that the given actions are realized by conjugation. If the actions are trivial, this can be done simply by forming the direct product of the two groups. In general, the question has a negative answer. One is led to the following construction. Let G and H be groups and suppose we are given fixed actions (g, h) 7→ gh and (h, g) 7→ hg of each group on the other. Received October 1, 1999. Mathematics Subject Classification. 20J05, 20E22, 20F05. Key words and phrases. homology, Peiffer product, asphericity, two-complex, double wreath product. -
Minimal Generation of Transitive Permutation Groups
Minimal generation of transitive permutation groups Gareth M. Tracey∗ Mathematics Institute, University of Warwick, Coventry CV4 7AL, United Kingdom October 30, 2017 Abstract This paper discusses upper bounds on the minimal number of elements d(G) required to generate a transitive permutation group G, in terms of its degree n, and its order G . In particular, we | | reduce a conjecture of L. Pyber on the number of subgroups of the symmetric group Sym(n). We also prove that our bounds are best possible. 1 Introduction A well-developed branch of finite group theory studies properties of certain classes of permutation groups as functions of their degree. The purpose of this paper is to study the minimal generation of transitive permutation groups. For a group G, let d(G) denote the minimal number of elements required to generate G. In [21], [7], [26] and [28], it is shown that d(G)= O(n/√log n) whenever G is a transitive permutation group of degree n 2 (here, and throughout this paper, “ log ” means log to the base 2). A beautifully ≥ constructed family of examples due to L. Kov´acs and M. Newman shows that this bound is ‘asymp- totically best possible’ (see Example 6.10), thereby ending the hope that a bound of d(G)= O(log n) could be proved. The constants involved in these theorems, however, were never estimated. We prove: arXiv:1504.07506v3 [math.GR] 30 Jan 2018 Theorem 1.1. Let G be a transitive permutation group of degree n 2. Then ≥ (1) d(G) cn ,where c := 1512660 log (21915)/(21915) = 0.920581 . -
Bounds of Some Invariants of Finite Permutation Groups Hülya Duyan
Bounds of Some Invariants of Finite Permutation Groups H¨ulya Duyan Department of Mathematics and its Applications Central European University Budapest, Hungary CEU eTD Collection A dissertation presented for the degree of Doctor of Philosophy in Mathematics CEU eTD Collection Abstract Let Ω be a non-empty set. A bijection of Ω onto itself is called a permutation of Ω and the set of all permutations forms a group under composition of mapping. This group is called the symmetric group on Ω and denoted by Sym(Ω) (or Sym(n) or Sn where jΩj = n). A permutation group on Ω is a subgroup of Sym(Ω). Until 1850's this was the definition of group. Although this definition and the ax- iomatic definition are the same, usually what we first learn is the axiomatic approach. The reason is to not to restrict the group elements to being permutations of some set Ω. Let G be a permutation group. Let ∼ be a relation on Ω such that α ∼ β if and only if there is a transformation g 2 G which maps α to β where α; β 2 Ω. ∼ is an equivalence relation on Ω and the equivalence classes of ∼ are the orbits of G. If there is one orbit then G is called transitive. Assume that G is intransitive and Ω1;:::; Ωt are the orbits of G on Ω. G induces a transitive permutation group on each Ωi, say Gi where i 2 f1; : : : ; tg. Gi are called the transitive constituents of G and G is a subcartesian product of its transitive constituents. -
A Survey on Automorphism Groups of Finite P-Groups
A Survey on Automorphism Groups of Finite p-Groups Geir T. Helleloid Department of Mathematics, Bldg. 380 Stanford University Stanford, CA 94305-2125 [email protected] February 2, 2008 Abstract This survey on the automorphism groups of finite p-groups focuses on three major topics: explicit computations for familiar finite p-groups, such as the extraspecial p-groups and Sylow p-subgroups of Chevalley groups; constructing p-groups with specified automorphism groups; and the discovery of finite p-groups whose automorphism groups are or are not p-groups themselves. The material is presented with varying levels of detail, with some of the examples given in complete detail. 1 Introduction The goal of this survey is to communicate some of what is known about the automorphism groups of finite p-groups. The focus is on three topics: explicit computations for familiar finite p-groups; constructing p-groups with specified automorphism groups; and the discovery of finite p-groups whose automorphism groups are or are not p-groups themselves. Section 2 begins with some general theorems on automorphisms of finite p-groups. Section 3 continues with explicit examples of automorphism groups of finite p-groups found in the literature. This arXiv:math/0610294v2 [math.GR] 25 Oct 2006 includes the computations on the automorphism groups of the extraspecial p- groups (by Winter [65]), the Sylow p-subgroups of the Chevalley groups (by Gibbs [22] and others), the Sylow p-subgroups of the symmetric group (by Bon- darchuk [8] and Lentoudis [40]), and some p-groups of maximal class and related p-groups. -
A Classification of Clifford Algebras As Images of Group Algebras of Salingaros Vee Groups
DEPARTMENT OF MATHEMATICS TECHNICAL REPORT A CLASSIFICATION OF CLIFFORD ALGEBRAS AS IMAGES OF GROUP ALGEBRAS OF SALINGAROS VEE GROUPS R. Ablamowicz,M.Varahagiri,A.M.Walley November 2017 No. 2017-3 TENNESSEE TECHNOLOGICAL UNIVERSITY Cookeville, TN 38505 A Classification of Clifford Algebras as Images of Group Algebras of Salingaros Vee Groups Rafa lAb lamowicz, Manisha Varahagiri and Anne Marie Walley Abstract. The main objective of this work is to prove that every Clifford algebra C`p;q is R-isomorphic to a quotient of a group algebra R[Gp;q] modulo an ideal J = (1 + τ) where τ is a central element of order 2. p+q+1 Here, Gp;q is a 2-group of order 2 belonging to one of Salingaros isomorphism classes N2k−1;N2k; Ω2k−1; Ω2k or Sk. Thus, Clifford al- gebras C`p;q can be classified by Salingaros classes. Since the group algebras R[Gp;q] are Z2-graded and the ideal J is homogeneous, the quotient algebras R[G]=J are Z2-graded. In some instances, the isomor- ∼ phism R[G]=J = C`p;q is also Z2-graded. By Salingaros Theorem, the groups Gp;q in the classes N2k−1 and N2k are iterative central products of the dihedral group D8 and the quaternion group Q8, and so they are extra-special. The groups in the classes Ω2k−1 and Ω2k are central products of N2k−1 and N2k with C2 × C2, respectively. The groups in the class Sk are central products of N2k or N2k with C4. Two algorithms to factor any Gp;q into an internal central product, depending on the class, are given. -
UCLA Electronic Theses and Dissertations
UCLA UCLA Electronic Theses and Dissertations Title Shapes of Finite Groups through Covering Properties and Cayley Graphs Permalink https://escholarship.org/uc/item/09b4347b Author Yang, Yilong Publication Date 2017 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA Los Angeles Shapes of Finite Groups through Covering Properties and Cayley Graphs A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Mathematics by Yilong Yang 2017 c Copyright by Yilong Yang 2017 ABSTRACT OF THE DISSERTATION Shapes of Finite Groups through Covering Properties and Cayley Graphs by Yilong Yang Doctor of Philosophy in Mathematics University of California, Los Angeles, 2017 Professor Terence Chi-Shen Tao, Chair This thesis is concerned with some asymptotic and geometric properties of finite groups. We shall present two major works with some applications. We present the first major work in Chapter 3 and its application in Chapter 4. We shall explore the how the expansions of many conjugacy classes is related to the representations of a group, and then focus on using this to characterize quasirandom groups. Then in Chapter 4 we shall apply these results in ultraproducts of certain quasirandom groups and in the Bohr compactification of topological groups. This work is published in the Journal of Group Theory [Yan16]. We present the second major work in Chapter 5 and 6. We shall use tools from number theory, combinatorics and geometry over finite fields to obtain an improved diameter bounds of finite simple groups. We also record the implications on spectral gap and mixing time on the Cayley graphs of these groups. -
On Finitely Generated Profinite Groups, Ii 241
Annals of Mathematics, 165 (2007), 239–273 On finitely generated profinite groups, II: products in quasisimple groups By Nikolay Nikolov* and Dan Segal Abstract We prove two results. (1) There is an absolute constant D such that for any finite quasisimple group S, given 2D arbitrary automorphisms of S, every element of S is equal to a product of D ‘twisted commutators’ defined by the given automorphisms. (2) Given a natural number q, there exist C = C(q) and M = M(q) such that: if S is a finite quasisimple group with |S/Z(S)| >C, βj (j =1,... ,M) are any automorphisms of S, and qj (j =1,... ,M) are any divisors of q, then M qj there exist inner automorphisms αj of S such that S = 1 [S, (αjβj) ]. These results, which rely on the classification of finite simple groups, are needed to complete the proofs of the main theorems of Part I. 1. Introduction The main theorems of Part I [NS] were reduced to two results about finite quasisimple groups. These will be proved here. A group S is said to be quasisimple if S =[S, S] and S/Z(S) is simple, where Z(S) denotes the centre of S. For automorphisms α and β of S we write −1 −1 α β Tα,β(x, y)=x y x y . Theorem 1.1. There is an absolute constant D ∈ N such that if S is a finite quasisimple group and α1,β1,... ,αD,βD are any automorphisms of S then ····· S = Tα1,β1 (S, S) TαD ,βD (S, S). -
Finite Simple Groups Which Projectively Embed in an Exceptional Lie Group Are Classified!
BULLETIN (New Series) OF THE AMERICAN MATHEMATICAL SOCIETY Volume 36, Number 1, January 1999, Pages 75{93 S 0273-0979(99)00771-5 FINITE SIMPLE GROUPS WHICH PROJECTIVELY EMBED IN AN EXCEPTIONAL LIE GROUP ARE CLASSIFIED! ROBERT L. GRIESS JR. AND A. J. E. RYBA Abstract. Since finite simple groups are the building blocks of finite groups, it is natural to ask about their occurrence “in nature”. In this article, we consider their occurrence in algebraic groups and moreover discuss the general theory of finite subgroups of algebraic groups. 0. Introduction Group character theory classifies embeddings of finite groups into classical groups. No general theory classifies embeddings into the exceptional complex al- gebraic group, i.e., one of G2(C), F4(C), E6(C), E7(C), E8(C). For exceptional groups, special methods seem necessary. Since the early 80s, there have been ef- forts to determine which central extensions of finite simple groups embed in an exceptional group. For short, we call this work a study of projective embeddings of finite simple groups into exceptional groups. Table PE on page 84 contains a summary. The classification program for finite subgroups of complex algebraic groups involves both existence of embeddings and their classification up to conjugacy. We have just classified embeddings of Sz(8) into E8(C) (there are three, up to E8(C)- conjugacy), thus settling the existence question for projective embeddings of finite simple groups into exceptional algebraic groups. The conjugacy part of the program is only partially resolved. The finite subgroups of the smallest simple algebraic group PSL(2; C)(upto conjugacy) constitute the famous list: cyclic, dihedral, Alt4, Sym4, Alt5. -
Arxiv:0712.4069V2 [Math.GR] 2 Jan 2008 Ooooycasswoersrcint N Bla Ugopof Subgroup Abelian Any to Restriction Whose Classes Cohomology by Denote Multiplier
THE BOGOMOLOV MULTIPLIER OF FINITE SIMPLE GROUPS BORIS KUNYAVSKI˘I Abstract. The subgroup of the Schur multiplier of a finite group G consisting of all cohomology classes whose restriction to any abelian subgroup of G is zero is called the Bogomolov multiplier of G. We prove that if G is quasisimple or almost simple, its Bogomolov multiplier is trivial. 1. Results Let G be a finite group, and let M(G) := H2(G, Q/Z) be its Schur multiplier. Denote by B0(G) the subgroup of M(G) consisting of the cohomology classes whose restriction to any abelian subgroup of G is zero. We call B0(G) the Bogomolov multiplier of G. This subgroup was introduced in [Bo87] in order to provide an explicit expression for the unramified Brauer group of the quotient V/G where V stands for any faithful linear representation of G over C. This birational invari- ant had earlier on been used by Saltman to give a negative answer to Noether’s problem [Sa]. The reader interested in historical perspective and geometric context is referred to [Sh], [CTS], [GS, 6.6, 6.7], [Bo07]. We say that G is quasisimple if G is perfect and its quotient by the arXiv:0712.4069v2 [math.GR] 2 Jan 2008 centre L = G/Z is a nonabelian simple group. We say that G is almost simple if for some nonabelian simple group L we have L ⊆ G ⊆ Aut L. Our first observation is Theorem 1.1. If G is a finite quasisimple group, then B0(G)=0. As a particular case, Theorem 1.1 contains the assertion on vanishing of B0(G) for all finite simple groups stated as a conjecture in [Bo92] and proved for the groups of Lie type An in [BMP]. -
Threads Through Group Theory
Contemporary Mathematics Threads Through Group Theory Persi Diaconis Abstract. This paper records the path of a letter that Marty Isaacs wrote to a stranger. The tools in the letter are used to illustrate a different way of studying random walk on the Heisenberg group. The author also explains how the letter contributed to the development of super-character theory. 1. Introduction Marty Isaacs believes in answering questions. They can come from students, colleagues, or perfect strangers. As long as they seem serious, he usually gives it a try. This paper records the path of a letter that Marty wrote to a stranger (me). His letter was useful; it is reproduced in the Appendix and used extensively in Section 3. It led to more correspondence and a growing set of extensions. Here is some background. I am a mathematical statistician who, for some unknown reason, loves finite group theory. I was trying to make my own peace with a corner of p-group theory called extra-special p-groups. These are p-groups G with center Z(G) equal to commutator subgroup G0 equal to the cyclic group Cp. I found considerable literature about the groups [2, Sect. 23], [22, Chap. III, Sect. 13], [39, Chap. 4, Sect. 4] but no \stories". Where do these groups come from? Who cares about them, and how do they fit into some larger picture? My usual way to understand a group is to invent a \natural" random walk and study its rate of convergence to the uniform distribution. This often calls for detailed knowledge of the conjugacy classes, characters, and of the geometry of the Cayley graph underlying the walk. -
Quasisimple Classical Groups and Their Complex Group Algebras
ISRAEL JOURNAL OF MATHEMATICS 195 (2013), 973–998 DOI: 10.1007/s11856-012-0142-9 QUASISIMPLE CLASSICAL GROUPS AND THEIR COMPLEX GROUP ALGEBRAS BY Hung Ngoc Nguyen Department of Mathematics, The University of Akron Akron, Ohio 44325, USA e-mail: [email protected] ABSTRACT Let H be a finite quasisimple classical group, i.e., H is perfect and S := H/Z(H) is a finite simple classical group. We prove that, excluding the open cases when S has a very exceptional Schur multiplier such as PSL3(4) or PSU4(3), H is uniquely determined by the structure of its complex group algebra. The proofs make essential use of the classification of finite simple groups as well as the results on prime power character degrees and relatively small character degrees of quasisimple classical groups. 1. Introduction A fundamental question in representation theory of finite groups is the extent to which the complex group algebra of a finite group determines the group ∼ or some of its properties. In the late 1980s, Isaacs proved that if CG = CH and p is a prime, then G has a normal p-complement if and only if H has a normal p-complement, and therefore the nilpotency of a group is determined by the complex group algebra of the group (cf. [Isa]). Later, Hawkes gave a counterexample showing that the same statement does not hold for supersolv- ability (cf. [Haw]). It is still unknown whether the solvability of a finite group is preserved by its complex group algebra (cf. [MaK, Problem 11.8]). While some properties of a solvable group G are determined by CG,itiswell ∼ known that G in general is not determined by CG. -
A Survey: Bob Griess's Work on Simple Groups and Their
Bulletin of the Institute of Mathematics Academia Sinica (New Series) Vol. 13 (2018), No. 4, pp. 365-382 DOI: 10.21915/BIMAS.2018401 A SURVEY: BOB GRIESS’S WORK ON SIMPLE GROUPS AND THEIR CLASSIFICATION STEPHEN D. SMITH Department of Mathematics (m/c 249), University of Illinois at Chicago, 851 S. Morgan, Chicago IL 60607-7045. E-mail: [email protected] Abstract This is a brief survey of the research accomplishments of Bob Griess, focusing on the work primarily related to simple groups and their classification. It does not attempt to also cover Bob’s many contributions to the theory of vertex operator algebras. (This is only because I am unqualified to survey that VOA material.) For background references on simple groups and their classification, I’ll mainly use the “outline” book [1] Over half of Bob Griess’s 85 papers on MathSciNet are more or less directly concerned with simple groups. Obviously I can only briefly describe the contents of so much work. (And I have left his work on vertex algebras etc to articles in this volume by more expert authors.) Background: Quasisimple components and the list of simple groups We first review some standard material from the early part of [1, Sec 0.3]. (More experienced readers can skip ahead to the subsequent subsection on the list of simple groups.) Received September 12, 2016. AMS Subject Classification: 20D05, 20D06, 20D08, 20E32, 20E42, 20J06. Key words and phrases: Simple groups, classification, Schur multiplier, standard type, Monster, code loops, exceptional Lie groups. 365 366 STEPHEN D. SMITH [December Components and the generalized Fitting subgroup The study of (nonabelian) simple groups leads naturally to consideration of groups L which are: quasisimple:namely,L/Z(L) is nonabelian simple; with L =[L, L].