DOCSLIB.ORG

On Non-Commuting Graphs of Dicyclic Group A

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
On Non-Commuting Graphs of Dicyclic Group A Sci.Int.(Lahore),29(1),7-11,2017 ISSN: 1013-5316; CODEN: SINTE 8 7 ON NON-COMMUTING GRAPHS OF DICYCLIC GROUP A. Mahboob1, Taswer Hussian2, ,M. Javaid3, Sajid Mahboob4 1,2Department of Mathematics, University of ducation, Lahore, Pakistan. [email protected] [email protected] 3Department of Mathematics,School of Science, University of Management and Technology (UMT), Lahore, Pakistan. [email protected]@gmail.com 4Departmentof Mathematics,MinhajUl-Quran University,Lahore. [email protected] ABSTRACT: For a given group G and a subset A⊆ G −Z(G), the non-commuting graph ∆ = [G, A] of the group G is a graph with vertex-set V(∆) = A such that two distinct vertices x, y ∈ V(∆) are connected by an edge i. e xy ∈ E(∆) if and only if xy = yx in G. In this paper, we study the certain properties of non-commuting graph on Dicyclic group 2n 2 n x DiCn = < a, x : a =1, x = a ,a = a−1> of order 4n and obtained certain parameters of graph theory as chromatic number, clique number and perfect matching. Keywords: Non-Commuting Graph, Dicyclic Group, Clique Number, Chromatic number. MR(2010) SubjectClassification:05C12. INTRODUCTION: triangles with exactly one common vertex, this common As we know, the algebraic structures pay a very important vertex is called the center of Fm. rule in the studies of different branches of Mathematics. A subset X of V(∆) is said to be clique if the sub graph The involvement of these structures in Graph Theory has induced by X is a complete graph. The maximum size of a become one of attractive research activities for clique in a graph ∆ is called clique number of ∆. It is Mathematicians of modern era. Therefore, in the literature, denoted by ω(∆). For k>0 (an integer), k-vertex coloring of there are many graphs like zero-divisor graphs, total graphs, the graph ∆ is an assignment of k-colors to the vertices of ∆ commutative graphs and non-commutative graphs. These such that no two adjacent vertices have same color. The graphs have been constructed from commutative rings and chromatic number of ∆ (denoted by χ(∆)) is the minimum k finite groups under certain algebraic properties of for which ∆ has k-vertex coloring. A graph ∆ is k-colorable idealization, modules, commutatively and non- (edge), if its edges can be colored with k-colors such that no commutatively, respectively. For a detail study, reader can 0 see [2,3, 5–7]. Now, we focus on the graphs, constructed two adjacent edges have same color. It is denoted by χ (∆) from finite groups. Segevand Seitz [13, 14] investigated the and called chromatic index of ∆. Length of minimal cycle in commuting graphs from non abelian simple groups. a graph ∆ is called girth of ∆. If u and v are the vertices in Iranmanesh and Jafarzadeh [9] associated the commuting ∆, the d(u, v) denotes the distance between u and v (length graphs with symmetric and alternating groups. In 2011, of shortest path between u and v). The largest distance Chelvametal. [8] and Mashkourietal. [10] found commutating between all the pairs of vertices of ∆ is called the diameter of graphs from dihedral groups. Abdullah oetal. [1] and ∆ and is denoted by dia(∆). A matching on a graph ∆ is a Moghaddam faretal. [11] constructed non-commuting graphs sub set of ∆ such that no two edges share a common vertex on different types of groups. In particularly, Asghar Talebi in it and order of this subset is called matching number of ∆ [4] constructed then on-commuting graphs of the Dihedral denoted by γ(G). The largest possible matching on a graph group. with n nodes consists of n/2 edges and such a matching is In this paper, we construct the non-commuting graphs from called a perfect matching. The center of a group G is denoted non-abelian and finite groups called dicyclic groups DiCn by Z(G) and defined as Z(G) = {x ∈G: xy = yx for all y with respect to its some specified sub sets. The of paper is ∈G}. Let a be any non-identity element to f G, then organized as follows ; the section 2 contains some notations centralizer of a in G is the set of elements of G which and basic definitions, while section 3 includes main results commutes with a and it is denoted by Ca(G). On the other of commuting graphs. hand, presents the set of elements which do 2 Preliminaries: Consider simple, finite and undirected graphs. For a graph ∆, not commute with a in G. we denote the vertex-set and edge-set by V(∆) and E(∆), Moreover, for a ∈A⊆G, Ca(G,A) is set of elements respectively. Moreover, m =|E(∆)|and n =|V(∆)| are called of A which commutes with a and size and order of the graph∆. The degree of a vertex v ∈ is set of elements of A which do not V(∆), denoted by deg∆(v) is number of incident edges on v. commute with a . Thus, if A=G, then A graph is regular if all the vertices are of same degree. A graph of order n is called a complete graph if each pair of Ca(G,A)=Ca(G) and = The Dicylic vertices is adjacent. It is denoted by Kn and is n−1 regular. group is represented by For n=2, it is also called a path of order 2 such that both vertices are of degree 1. A friendship graph Fm consists of m January-February 8 ISSN: 1013-5316; CODEN: SINTE 8 Sci.Int.(Lahore),29(1),7-11,2017 2n 2 n x −1 (ii) If A = DiC −Z(DiC ), then non-commuting graph is DiCn = <a, x: a =1, x =a , a =a > under the n n following multiplication rules; (i) asat=as+t, (ii) multipartite graph. So, dia(∆) = 2. Theorem3.3. For n ≥ 2 and A ⊆ DiC , if ∆ = [DiC , A] asatx=as+tx, n n s t s−t is a non-commuting graph. Then, (i) ∆ is an empty graph of (iii) a xa =a x, order 2 ⇔A= Bi for some i∈ I2 or A = X, where X⊂A1 s t s−t+n (iv) a xa x=a . such that |X| = 2. It is a member of a class of non-abelian groups of (i) ∆ is an empty graph of order 2n−2⇔A = A1. order 4n, where n>1. Every element of Dicyclic (ii) ∆ = Kn+1⇔A= C1∪{u}or C2∪{u} for some u∈ i j group can be written in the forma x , where A1 . i∈{0,1,2,...,2n−1} and j is 0 or 1. Suppose that Proof: (i)(case-i) Assume that ∆ = [DiC ,A] is an on-commuting graph such I1= {1,2,...,n−1,n+1,...,2n−1}, n that A = B for some i∈ I . As = Φ I2= {1,2,...,n}, I3={n+1,n+2,...,2n} i 2 i and I4=I2∪I3then = for each i∈ I2 ⇒ deg∆(a ) = 0 = i i n+I i A1 = {a : i∈ I1}, Bi={a x, a x:i∈I2}, deg∆(a x). i B=⋃ ∈ C1= {a x:i∈ I2}, i Moreover, |Bi| = 2 for each i∈ I2. Thus, ∆ is an empty C2 = {a x:i∈ I3}, graph of order 2. (case-ii)Assume that ∆=[DiCn, A] is a ai aix Di = { , :i∈ I1}, non-commuting graph such that A=X, where X ⊂A1 with are suitable subsets of DiCn. |X| = 2. As each element of A1 commutes with others in 3 MAIN RESULTS A1, there for both element of X, say a and b commutes with In this section, we present the main results of the each other. Thus, =Φ= non-commuting graphs ∆ = [DiCn, A], Where A ⇒ deg∆(a) =0 = deg∆(b). Thus, ∆ is an empty graph of order ⊆ DiCn. 2. Conversely, assume that ∆ = [DiCn, A] is a non- Lemma3.1. For n≥2 and A = DiCn, if ∆ = commuting graph such that ∆ is an empty graphoforder2. Let [DiCn, A] is a non-commuting graph. Then, v ∈ A⇒ v ∈ V(∆)⇒ deg ∆(v) = 0 ⇒. Thus, v ∈ Bi for some i∈ I or v ∈ X. If v ∈ B for some I ∈ I ⇒A ⊆ B and also 2n, for v ∈ A1 2 i 2 i B ⊆A. Consequently, A=B for some i. If v ∈ X ⇒A ⊆X ∈ i i deg∆(v)={ and also X ⊆A. Consequently, A=X. ∈ i (ii) Assume that ∆ =[DiCn,A] is a non-commuting graph Proof: Let v = a ∈ A1, where i ∈ I1.Then, such that A=A1.As j (DiCn) = {a x: j= 1,2,...,2n}. =Φ for each a ∈ A1 ⇒deg ∆(a) = 0 for each i Therefore, for i∈ I1, we have deg∆(a ) = 2n. a∈ A1.Thus, ∆ is an empty graph. Also |A| = 2n −2 ⇒ ∆ is Consequently, deg∆(v) = 2n for each v ∈ A1. anemptygraphoforder2n−2.Conversely, assume that ∆ = [DiC , A] is a non-commuting graph such that For v = aix ∈ B , where i ∈ {1, 2, 3,..., 2n}, we n ∆ is an empty graph of order 2n−2. Let v∈ A ⇒ v ∈ V(∆) ⇒ j have Caix(DiCn) = {a x: j = 1, 2, ..., 2n, j I and deg ∆(v) = 0⇒ v commutes with each element of A. Thus, j i v ∈ A ⇒A⊆ A and also A ⊆ A. Consequently, A = A . j n +i}∪{a : j∈ I1}. Thus, deg∆(a x) = 1 1 1 1 4(n−1) ⇒ deg∆(v) = 4 (n−1) for v∈ B deg∆ (iii) Assume that ∆ = [Di Cn,A] is a non-commuting graph i (a x) = 4(n−1)⇒deg∆(v) = 4 (n−1) for v ∈ B such that A= C1∪{u}, where u ∈A1.
Load more

Recommended publications
  • The Classification and the Conjugacy Classesof the Finite Subgroups of The
    Algebraic & Geometric Topology 8 (2008) 757–785 757 The classification and the conjugacy classes of the finite subgroups of the sphere braid groups DACIBERG LGONÇALVES JOHN GUASCHI Let n 3. We classify the finite groups which are realised as subgroups of the sphere 2 braid group Bn.S /. Such groups must be of cohomological period 2 or 4. Depend- ing on the value of n, we show that the following are the maximal finite subgroups of 2 Bn.S /: Z2.n 1/ ; the dicyclic groups of order 4n and 4.n 2/; the binary tetrahedral group T ; the binary octahedral group O ; and the binary icosahedral group I . We give geometric as well as some explicit algebraic constructions of these groups in 2 Bn.S / and determine the number of conjugacy classes of such finite subgroups. We 2 also reprove Murasugi’s classification of the torsion elements of Bn.S / and explain 2 how the finite subgroups of Bn.S / are related to this classification, as well as to the 2 lower central and derived series of Bn.S /. 20F36; 20F50, 20E45, 57M99 1 Introduction The braid groups Bn of the plane were introduced by E Artin in 1925[2;3]. Braid groups of surfaces were studied by Zariski[41]. They were later generalised by Fox to braid groups of arbitrary topological spaces via the following definition[16]. Let M be a compact, connected surface, and let n N . We denote the set of all ordered 2 n–tuples of distinct points of M , known as the n–th configuration space of M , by: Fn.M / .p1;:::; pn/ pi M and pi pj if i j : D f j 2 ¤ ¤ g Configuration spaces play an important roleˆ in several branches of mathematics and have been extensively studied; see Cohen and Gitler[9] and Fadell and Husseini[14], for example.
    [Show full text]
  • INTEGRAL CAYLEY GRAPHS and GROUPS 3 of G on W
    INTEGRAL CAYLEY GRAPHS AND GROUPS AZHVAN AHMADY, JASON P. BELL, AND BOJAN MOHAR Abstract. We solve two open problems regarding the classification of certain classes of Cayley graphs with integer eigenvalues. We first classify all finite groups that have a “non-trivial” Cayley graph with integer eigenvalues, thus solving a problem proposed by Abdollahi and Jazaeri. The notion of Cayley integral groups was introduced by Klotz and Sander. These are groups for which every Cayley graph has only integer eigenvalues. In the second part of the paper, all Cayley integral groups are determined. 1. Introduction A graph X is said to be integral if all eigenvalues of the adjacency matrix of X are integers. This property was first defined by Harary and Schwenk [9] who suggested the problem of classifying integral graphs. This problem ignited a signifi- cant investigation among algebraic graph theorists, trying to construct and classify integral graphs. Although this problem is easy to state, it turns out to be extremely hard. It has been attacked by many mathematicians during the last forty years and it is still wide open. Since the general problem of classifying integral graphs seems too difficult, graph theorists started to investigate special classes of graphs, including trees, graphs of bounded degree, regular graphs and Cayley graphs. What proves so interesting about this problem is that no one can yet identify what the integral trees are or which 5-regular graphs are integral. The notion of CIS groups, that is, groups admitting no integral Cayley graphs besides complete multipartite graphs, was introduced by Abdollahi and Jazaeri [1], who classified all abelian CIS groups.
    [Show full text]
  • Generalized Quaternions
    GENERALIZED QUATERNIONS KEITH CONRAD 1. introduction The quaternion group Q8 is one of the two non-abelian groups of size 8 (up to isomor- phism). The other one, D4, can be constructed as a semi-direct product: ∼ ∼ × ∼ D4 = Aff(Z=(4)) = Z=(4) o (Z=(4)) = Z=(4) o Z=(2); where the elements of Z=(2) act on Z=(4) as the identity and negation. While Q8 is not a semi-direct product, it can be constructed as the quotient group of a semi-direct product. We will see how this is done in Section2 and then jazz up the construction in Section3 to make an infinite family of similar groups with Q8 as the simplest member. In Section4 we will compare this family with the dihedral groups and see how it fits into a bigger picture. 2. The quaternion group from a semi-direct product The group Q8 is built out of its subgroups hii and hji with the overlapping condition i2 = j2 = −1 and the conjugacy relation jij−1 = −i = i−1. More generally, for odd a we have jaij−a = −i = i−1, while for even a we have jaij−a = i. We can combine these into the single formula a (2.1) jaij−a = i(−1) for all a 2 Z. These relations suggest the following way to construct the group Q8. Theorem 2.1. Let H = Z=(4) o Z=(4), where (a; b)(c; d) = (a + (−1)bc; b + d); ∼ The element (2; 2) in H has order 2, lies in the center, and H=h(2; 2)i = Q8.
    [Show full text]
  • 12.6 Further Topics on Simple Groups 387 12.6 Further Topics on Simple Groups
    12.6 Further Topics on Simple groups 387 12.6 Further Topics on Simple Groups This Web Section has three parts (a), (b) and (c). Part (a) gives a brief descriptions of the 56 (isomorphism classes of) simple groups of order less than 106, part (b) provides a second proof of the simplicity of the linear groups Ln(q), and part (c) discusses an ingenious method for constructing a version of the Steiner system S(5, 6, 12) from which several versions of S(4, 5, 11), the system for M11, can be computed. 12.6(a) Simple Groups of Order less than 106 The table below and the notes on the following five pages lists the basic facts concerning the non-Abelian simple groups of order less than 106. Further details are given in the Atlas (1985), note that some of the most interesting and important groups, for example the Mathieu group M24, have orders in excess of 108 and in many cases considerably more. Simple Order Prime Schur Outer Min Simple Order Prime Schur Outer Min group factor multi. auto. simple or group factor multi. auto. simple or count group group N-group count group group N-group ? A5 60 4 C2 C2 m-s L2(73) 194472 7 C2 C2 m-s ? 2 A6 360 6 C6 C2 N-g L2(79) 246480 8 C2 C2 N-g A7 2520 7 C6 C2 N-g L2(64) 262080 11 hei C6 N-g ? A8 20160 10 C2 C2 - L2(81) 265680 10 C2 C2 × C4 N-g A9 181440 12 C2 C2 - L2(83) 285852 6 C2 C2 m-s ? L2(4) 60 4 C2 C2 m-s L2(89) 352440 8 C2 C2 N-g ? L2(5) 60 4 C2 C2 m-s L2(97) 456288 9 C2 C2 m-s ? L2(7) 168 5 C2 C2 m-s L2(101) 515100 7 C2 C2 N-g ? 2 L2(9) 360 6 C6 C2 N-g L2(103) 546312 7 C2 C2 m-s L2(8) 504 6 C2 C3 m-s
    [Show full text]
  • Supplement. Direct Products and Semidirect Products
    Supplement: Direct Products and Semidirect Products 1 Supplement. Direct Products and Semidirect Products Note. In Section I.8 of Hungerford, we defined direct products and weak direct n products. Recall that when dealing with a finite collection of groups {Gi}i=1 then the direct product and weak direct product coincide (Hungerford, page 60). In this supplement we give results concerning recognizing when a group is a direct product of smaller groups. We also define the semidirect product and illustrate its use in classifying groups of small order. The content of this supplement is based on Sections 5.4 and 5.5 of Davis S. Dummitt and Richard M. Foote’s Abstract Algebra, 3rd Edition, John Wiley and Sons (2004). Note. Finitely generated abelian groups are classified in the Fundamental Theo- rem of Finitely Generated Abelian Groups (Theorem II.2.1). So when addressing direct products, we are mostly concerned with nonabelian groups. Notice that the following definition is “dull” if applied to an abelian group. Definition. Let G be a group, let x, y ∈ G, and let A, B be nonempty subsets of G. (1) Define [x, y]= x−1y−1xy. This is the commutator of x and y. (2) Define [A, B]= h[a,b] | a ∈ A,b ∈ Bi, the group generated by the commutators of elements from A and B where the binary operation is the same as that of group G. (3) Define G0 = {[x, y] | x, y ∈ Gi, the subgroup of G generated by the commuta- tors of elements from G under the same binary operation of G.
    [Show full text]
  • Universality of Single-Qudit Gates
    Ann. Henri Poincar´e Online First c 2017 The Author(s). This article is an open access publication Annales Henri Poincar´e DOI 10.1007/s00023-017-0604-z Universality of Single-Qudit Gates Adam Sawicki and Katarzyna Karnas Abstract. We consider the problem of deciding if a set of quantum one- qudit gates S = {g1,...,gn}⊂G is universal, i.e. if <S> is dense in G, where G is either the special unitary or the special orthogonal group. To every gate g in S we assign the orthogonal matrix Adg that is image of g under the adjoint representation Ad : G → SO(g)andg is the Lie algebra of G. The necessary condition for the universality of S is that the only matrices that commute with all Adgi ’s are proportional to the identity. If in addition there is an element in <S> whose Hilbert–Schmidt distance √1 S from the centre of G belongs to ]0, 2 [, then is universal. Using these we provide a simple algorithm that allows deciding the universality of any set of d-dimensional gates in a finite number of steps and formulate a general classification theorem. 1. Introduction Quantum computer is a device that operates on a finite-dimensional quantum system H = H1 ⊗···⊗Hn consisting of n qudits [4,19,28] that are described by d d-dimensional Hilbert spaces, Hi C [29]. When d = 2 qudits are typically called qubits. The ability to effectively manufacture optical gates operating on many modes, using, for example, optical networks that couple modes of light [9,33,34], is a natural motivation to consider not only qubits but also higher- dimensional systems in the quantum computation setting (see also [30,31] for the case of fermionic linear optics and quantum metrology).
    [Show full text]
  • The Classification and the Conjugacy Classes of the Finite Subgroups of the Sphere Braid Groups Daciberg Gonçalves, John Guaschi
    The classification and the conjugacy classes of the finite subgroups of the sphere braid groups Daciberg Gonçalves, John Guaschi To cite this version: Daciberg Gonçalves, John Guaschi. The classification and the conjugacy classes of the finite subgroups of the sphere braid groups. Algebraic and Geometric Topology, Mathematical Sciences Publishers, 2008, 8 (2), pp.757-785. 10.2140/agt.2008.8.757. hal-00191422 HAL Id: hal-00191422 https://hal.archives-ouvertes.fr/hal-00191422 Submitted on 26 Nov 2007 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. The classification and the conjugacy classes of the finite subgroups of the sphere braid groups DACIBERG LIMA GONC¸ALVES Departamento de Matem´atica - IME-USP, Caixa Postal 66281 - Ag. Cidade de S˜ao Paulo, CEP: 05311-970 - S˜ao Paulo - SP - Brazil. e-mail: [email protected] JOHN GUASCHI Laboratoire de Math´ematiques Nicolas Oresme UMR CNRS 6139, Universit´ede Caen BP 5186, 14032 Caen Cedex, France. e-mail: [email protected] 21st November 2007 Abstract Let n ¥ 3. We classify the finite groups which are realised as subgroups of the sphere braid 2 Õ group Bn ÔS .
    [Show full text]
  • Quaternionic Root Systems and Subgroups of the $ Aut (F {4}) $
    Quaternionic Root Systems and Subgroups of the Aut(F4) Mehmet Koca∗ and Muataz Al-Barwani† Department of Physics, College of Science, Sultan Qaboos University, PO Box 36, Al-Khod 123, Muscat, Sultanate of Oman Ramazan Ko¸c‡ Department of Physics, Faculty of Engineering University of Gaziantep, 27310 Gaziantep, Turkey (Dated: November 12, 2018) Cayley-Dickson doubling procedure is used to construct the root systems of some celebrated Lie algebras in terms of the integer elements of the division algebras of real numbers, complex numbers, quaternions and octonions. Starting with the roots and weights of SU(2) expressed as the real numbers one can construct the root systems of the Lie algebras of SO(4), SP (2) ≈ SO(5), SO(8), SO(9), F4 and E8 in terms of the discrete elements of the division algebras. The roots themselves display the group structures besides the octonionic roots of E8 which form a closed octonion algebra. The automorphism group Aut(F4) of the Dynkin diagram of F4 of order 2304, the largest crystallographic group in 4-dimensional Euclidean space, is realized as the direct product of two binary octahedral group of quaternions preserving the quaternionic root system of F4 .The Weyl groups of many Lie algebras, such as, G2, SO(7), SO(8), SO(9), SU(3)XSU(3) and SP (3) × SU(2) have been constructed as the subgroups of Aut(F4) .We have also classified the other non-parabolic subgroups of Aut(F4) which are not Weyl groups. Two subgroups of orders192 with different conju- gacy classes occur as maximal subgroups in the finite subgroups of the Lie group G2 of orders 12096 and 1344 and proves to be useful in their constructions.
    [Show full text]
  • On Some Probabilistic Aspects of (Generalized) Dicyclic Groups
    On some probabilistic aspects of (generalized) dicyclic groups Marius T˘arn˘auceanu and Mihai-Silviu Lazorec December 6, 2016 Abstract In this paper we study probabilistic aspects such as subgroup com- mutativity degree and cyclic subgroup commutativity degree of the (generalized) dicyclic groups. We find explicit formulas for these con- cepts and we provide another example of a class of groups whose (cyclic) subgroup commutativity degree vanishes asymptotically. MSC (2010): Primary 20D60, 20P05; Secondary 20D30, 20F16, 20F18. Key words: subgroup commutativity degree, subgroup lattice, cyclic sub- group commutativity degree, poset of cyclic subgroups. 1 Introduction The link between finite groups and probability theories is a topic which is frequently studied in the last years. Given a finite group G, many results regarding the appartenence of G to a class of groups were obtained using a arXiv:1612.01967v1 [math.GR] 6 Dec 2016 relevant concept known as the commutativity degree of G which measures the probability that two elements of the group commute. We refer the reader to [2, 3] and [5]-[9] for more details. Inspired by this notion, in [15, 21], we introduced another two probabilistic aspects called the subgroup commuta- tivity degree and the cyclic subgroup commutativity degree of a finite group G. Denoting by L(G) and L1(G) the subgroup lattice and the poset of cyclic subgoups of G, respectively, the above concepts are defined by 1 sd(G)= {(H,K) ∈ L(G)2|HK = KH} = |L(G)|2 1 1 = {(H,K) ∈ L(G)2|HK ∈ L(G)} |L(G)|2 and 1 csd G H,K L G 2 HK KH ( )= 2 {( ) ∈ 1( ) | = } = |L1(G)| 1 H,K L G 2 HK L G , = 2 {( ) ∈ 1( ) | ∈ 1( )} |L1(G)| respectively.
    [Show full text]
  • The Classification and the Conjugacy Classes of the Finite Subgroups Of
    The classification and the conjugacy classes of the finite subgroups of the sphere braid groups DACIBERG LIMA GONÇALVES Departamento de Matemática - IME-USP, Caixa Postal 66281 - Ag. Cidade de São Paulo, CEP: 05311-970 - São Paulo - SP - Brazil. e-mail: JOHN GUASCHI Laboratoire de Mathématiques Nicolas Oresme UMR CNRS 6139, Université de Caen BP 5186, 14032 Caen Cedex, France. e-mail: ºÖ 21st November 2007 Abstract Let n ¥ 3. We classify the finite groups which are realised as subgroups of the sphere braid 2 Õ group Bn ÔS . Such groups must be of cohomological period 2 or 4. Depending on the 2 Ô Õ ¡ Õ value of n, we show that the following are the maximal finite subgroups of Bn S : Z2Ô n 1 ; ¡ Õ the dicyclic groups of order 4n and 4Ô n 2 ; the binary tetrahedral group T1; the binary octahedral group O1; and the binary icosahedral group I. We give geometric as well as 2 Õ some explicit algebraic constructions of these groups in Bn ÔS , and determine the number arXiv:0711.3968v1 [math.GT] 26 Nov 2007 of conjugacy classes of such finite subgroups. We also reprove Murasugi’s classification of 2 2 Õ Ô Õ the torsion elements of Bn ÔS , and explain how the finite subgroups of Bn S are related 2 Õ to this classification, as well as to the lower central and derived series of Bn ÔS . 1 Introduction The braid groups Bn of the plane were introduced by E. Artin in 1925 [A1, A2]. Braid groups of surfaces were studied by Zariski [Z].
    [Show full text]
  • Quaternionic Roots of E8 Related Coxeter Graphs and Quasicrystals∗
    Tr. J. of Physics 22 (1998) , 421 – 435. c TUB¨ ITAK˙ Quaternionic Roots of E8 Related Coxeter Graphs and Quasicrystals∗ Mehmet KOCA, Nazife Ozde¸¨ sKOCA Department of Physics, College of Science, Sultan Qaboos University, P.O. Box 36, Al-Khod 123 Muscat, Sultanate of Oman, Department of Physics, C¸ ukurova University, 01330 Adana - TURKEY Ramazan KOC¸ Department of Physics, C¸ukurova University, 01330 Adana - TURKEY Received 25.02.1997 Abstract The lattice matching of two sets of quaternionic roots of F4 leads to quaternionic roots of E8 which has a decomposition H4 + σH4 where the Coxeter graph H4 is represented by the 120 quaternionic elements of the binary icosahedral group. The 30 pure imaginary quaternions constitute the roots of H3 which has a natural extension to H3 +σH3 describing the root system of the Lie algebra D6 . It is noted that there exist three lattices in 6-dimensions whose point group W(D6) admits the icosahedral symmetry H3 as a subgroup, the roots of which describe the mid-points of the edges of an icosahedron. A natural extension of the Coxeter group H2 of order 10 is the Weyl group W(A4)whereH2 + σH2 constitute the root system of the Lie algebra A4 . The relevance of these systems to quasicrystals are discussed. 1. Introduction Emergence of the noncrystallographic Coxeter graph H3 in SU(3) conformal field theory [1] motivates further studies of the noncrystallographic Coxeter graphs H2,H3 , and H4 and the associated Coxeter-Dynkin diagrams which naturally admit them as subgraphs. They are the respective Weyl groups W (A4),W(D6)andW (E8) generated by reflections.
    [Show full text]
  • Introduction to Groups 1
    Contents Contents i List of Figures ii List of Tables iii 1 Introduction to Groups 1 1.1 Disclaimer .............................................. 1 1.2 Why Study Group Theory? .................................... 1 1.2.1 Discrete and continuous symmetries .......................... 1 1.2.2 Symmetries in quantum mechanics ........................... 2 1.3 Formal definition of a discrete group ............................... 3 1.3.1 Group properties ..................................... 3 1.3.2 The Cayley table ...................................... 4 1.3.3 Loopsand groups ..................................... 4 1.3.4 The equilateral triangle : C3v and C3 .......................... 5 1.3.5 Symmetry breaking .................................... 8 1.3.6 The dihedralgroup Dn .................................. 9 1.3.7 The permutation group Sn ................................ 10 1.3.8 Our friend, SU(2) ..................................... 12 1.4 Aspects of Discrete Groups .................................... 14 1.4.1 Basic features of discrete groups ............................. 14 i ii CONTENTS 1.4.2 Other math stuff ...................................... 18 1.4.3 More about permutations ................................. 19 1.4.4 Conjugacy classes of the dihedral group ........................ 21 1.4.5 Quaternion group ..................................... 21 1.4.6 Group presentations .................................... 23 1.5 Lie Groups .............................................. 25 1.5.1 DefinitionofaLiegroup ................................
    [Show full text]