scholarly journals ON A CLASS OF EDGE-TRANSITIVE DISTANCE-REGULAR ANTIPODAL COVERS OF COMPLETE GRAPHS

2021 ◽  
Vol 7 (2) ◽  
pp. 136
Author(s):  
Ludmila Yu. Tsiovkina
Keyword(s):  
Automorphism Group ◽  
Automorphism Groups ◽  
Satisfying Condition ◽  
Complete Graphs ◽  
Transitive Graph ◽  
Common Neighbour ◽  
Moore Graph ◽  
Antipodal Cover ◽  
Edge Transitive

The paper is devoted to the problem of classification of edge-transitive distance-regular antipodal covers of complete graphs. This extends the classification of those covers that are arc-transitive, which has been settled except for some tricky cases that remain to be considered, including the case of covers satisfying condition \(c_2=1\) (which means that every two vertices at distance 2  have exactly one common neighbour).Here it is shown that an edge-transitive distance-regular antipodal cover of a complete graph with \(c_2=1\) is either the second neighbourhood of a vertex in a Moore graph of valency 3 or 7, or a Mathon graph, or a half-transitive graph whose automorphism group induces an affine  \(2\)-homogeneous group on the set of its fibres. Moreover,  distance-regular  antipodal covers of complete graphs  with \(c_2=1\) that admit  an automorphism group acting  \(2\)-homogeneously on the set of fibres (which turns out to be an approximation of the property of edge-transitivity  of such  cover), are described.   A well-known correspondence between distance-regular antipodal covers of complete graphs with \(c_2=1\) and geodetic graphs of diameter two that can be viewed as underlying graphs of certain Moore geometries, allows us to effectively restrict admissible automorphism groups of covers under consideration by combining Kantor's classification of involutory automorphisms of these geometries together with the classification of finite 2-homogeneous permutation groups.

Automorphism Groups of Bouwer Graphs

2018 ◽  
Vol 25 (03) ◽  
pp. 493-508 ◽  
Author(s):  
Mimi Zhang ◽  
Jinxin Zhou
Keyword(s):  
Automorphism Group ◽  
Automorphism Groups ◽  
Transitive Graph ◽  
Full Automorphism Group ◽  
Vertex Set ◽  
Edge Transitive ◽  
Positive Integers

Let k, m and n be three positive integers such that 2m ≡ 1 (mod n) and k ≥ 2. The Bouwer graph, which is denoted by B(k, m, n), is the graph with vertex set [Formula: see text] and two vertices being adjacent if they can be written as (a, b) and (a + 1, c), where either c = b or [Formula: see text] differs from [Formula: see text] in exactly one position, say the jth position, where [Formula: see text]. Every B(k, m, n) is a vertex- and edge-transitive graph, and Bouwer proved that B(k, 6, 9) is half-arc-transitive for every k ≥ 2. In 2016, Conder and Žitnik gave the classification of half-arc-transitive Bouwer graphs. In this paper, the full automorphism group of every B(k, m, n) is determined.

On the Classification of Rational Quantum Tori and the Structure of Their Automorphism Groups

2008 ◽  
Vol 51 (2) ◽  
pp. 261-282 ◽  
Author(s):  
Karl-Hermann Neeb
Keyword(s):  
Automorphism Group ◽  
Normal Form ◽  
Exact Sequence ◽  
Present Note ◽  
Automorphism Groups ◽  
Roots Of Unity ◽  
Quantum Torus ◽  
Twisted Group Algebra ◽  
Quantum Tori

AbstractAn n-dimensional quantum torus is a twisted group algebra of the group ℤn. It is called rational if all invertible commutators are roots of unity. In the present note we describe a normal form for rational n-dimensional quantum tori over any field. Moreover, we show that for n = 2 the natural exact sequence describing the automorphism group of the quantum torus splits over any field.

scholarly journals CLASSIFICATION OF TETRAVALENT -TRANSITIVE NONNORMAL CAYLEY GRAPHS OF FINITE SIMPLE GROUPS

2021 ◽  
pp. 1-9
Author(s):  
XIN GUI FANG ◽  
JIE WANG ◽  
SANMING ZHOU
Keyword(s):  
Automorphism Group ◽  
Simple Group ◽  
Cayley Graph ◽  
Finite Simple Group ◽  
Cayley Graphs ◽  
Simple Groups ◽  
Finite Simple Groups ◽  
Edge Transitive

Abstract A graph $\Gamma $ is called $(G, s)$ -arc-transitive if $G \le \text{Aut} (\Gamma )$ is transitive on the set of vertices of $\Gamma $ and the set of s-arcs of $\Gamma $ , where for an integer $s \ge 1$ an s-arc of $\Gamma $ is a sequence of $s+1$ vertices $(v_0,v_1,\ldots ,v_s)$ of $\Gamma $ such that $v_{i-1}$ and $v_i$ are adjacent for $1 \le i \le s$ and $v_{i-1}\ne v_{i+1}$ for $1 \le i \le s-1$ . A graph $\Gamma $ is called 2-transitive if it is $(\text{Aut} (\Gamma ), 2)$ -arc-transitive but not $(\text{Aut} (\Gamma ), 3)$ -arc-transitive. A Cayley graph $\Gamma $ of a group G is called normal if G is normal in $\text{Aut} (\Gamma )$ and nonnormal otherwise. Fang et al. [‘On edge transitive Cayley graphs of valency four’, European J. Combin.25 (2004), 1103–1116] proved that if $\Gamma $ is a tetravalent 2-transitive Cayley graph of a finite simple group G, then either $\Gamma $ is normal or G is one of the groups $\text{PSL}_2(11)$ , $\text{M} _{11}$ , $\text{M} _{23}$ and $A_{11}$ . However, it was unknown whether $\Gamma $ is normal when G is one of these four groups. We answer this question by proving that among these four groups only $\text{M} _{11}$ produces connected tetravalent 2-transitive nonnormal Cayley graphs. We prove further that there are exactly two such graphs which are nonisomorphic and both are determined in the paper. As a consequence, the automorphism group of any connected tetravalent 2-transitive Cayley graph of any finite simple group is determined.

scholarly journals Regular dessins uniquely determined by a nilpotent automorphism group

2018 ◽  
Vol 21 (3) ◽  
pp. 397-415 ◽  
Author(s):  
Na-Er Wang ◽  
Roman Nedela ◽  
Kan Hu
Keyword(s):  
Finite Group ◽  
Automorphism Group ◽  
Upper Bound ◽  
Automorphism Groups ◽  
Nilpotency Class ◽  
Isomorphism Classes ◽  
One To One

Abstract It is well known that the automorphism group of a regular dessin is a two-generator finite group, and the isomorphism classes of regular dessins with automorphism groups isomorphic to a given finite group G are in one-to-one correspondence with the orbits of the action of {{\mathrm{Aut}}(G)} on the ordered generating pairs of G. If there is only one orbit, then up to isomorphism the regular dessin is uniquely determined by the group G and it is called uniquely regular. In this paper we investigate the classification of uniquely regular dessins with a nilpotent automorphism group. The problem is reduced to the classification of finite maximally automorphic p-groups G, i.e., the order of the automorphism group of G attains Hall’s upper bound. Maximally automorphic p-groups of nilpotency class three are classified.

scholarly journals Automorphisms and periods of cubic fourfolds

2021 ◽  
Author(s):  
Radu Laza ◽  
Zhiwei Zheng
Keyword(s):  
Fixed Point ◽  
Automorphism Group ◽  
Automorphism Groups ◽  
Leech Lattice ◽  
Torelli Theorem ◽  
Symplectic Automorphisms ◽  
Cubic Fourfold

AbstractWe classify the symplectic automorphism groups for cubic fourfolds. The main inputs are the global Torelli theorem for cubic fourfolds and the classification of the fixed-point sublattices of the Leech lattice. Among the highlights of our results, we note that there are 34 possible groups of symplectic automorphisms, with 6 maximal cases. The six maximal cases correspond to 8 non-isomorphic, and isolated in moduli, cubic fourfolds; six of them previously identified by other authors. Finally, the Fermat cubic fourfold has the largest possible order (174, 960) for the automorphism group (non-necessarily symplectic) among all smooth cubic fourfolds.

Local Expansion of Symmetrical Graphs

1992 ◽  
Vol 1 (1) ◽  
pp. 1-11 ◽  
Author(s):  
László Babai ◽  
Mario Szegedy
Keyword(s):  
Automorphism Group ◽  
Finite Subset ◽  
Harmonic Mean ◽  
Expansion Rate ◽  
Transitive Graph ◽  
Local Expansion ◽  
Vertex Set ◽  
Vertex Transitive ◽  
Edge Transitive ◽  
Vertex Transitive Graph

A graph is vertex-transitive (edge-transitive) if its automorphism group acts transitively on the vertices (edges, resp.). The expansion rate of a subset S of the vertex set is the quotient e(S):= |∂(S)|/|S|, where ∂(S) denotes the set of vertices not in S but adjacent to some vertex in S. Improving and extending previous results of Aldous and Babai, we give very simple proofs of the following results. Let X be a (finite or infinite) vertex-transitive graph and let S be a finite subset of the vertices. If X is finite, we also assume |S| ≤|V(X)/2. Let d be the diameter of S in the metric induced by X. Then e(S) ≥1/(d + 1); and e(S) ≥ 2/(d +2) if X is finite and d is less than the diameter of X. If X is edge-transitive then |δ(S)|/|S| ≥ r/(2d), where ∂(S) denotes the set of edges joining S to its complement and r is the harmonic mean of the minimum and maximum degrees of X. – Diverse applications of the results are mentioned.

On quasiprimitive edge-transitive graphs of odd order and twice prime valency

2020 ◽  
Vol 23 (6) ◽  
pp. 1017-1037
Author(s):  
Hong Ci Liao ◽  
Jing Jian Li ◽  
Zai Ping Lu
Keyword(s):  
Automorphism Group ◽  
Connected Graph ◽  
Automorphism Groups ◽  
Primitive Group ◽  
Odd Order ◽  
Vertex Set ◽  
Edge Transitive ◽  
Affine Type ◽  
Transitive Graphs

AbstractA graph is edge-transitive if its automorphism group acts transitively on the edge set. In this paper, we investigate the automorphism groups of edge-transitive graphs of odd order and twice prime valency. Let {\varGamma} be a connected graph of odd order and twice prime valency, and let G be a subgroup of the automorphism group of {\varGamma}. In the case where G acts transitively on the edge set and quasiprimitively on the vertex set of {\varGamma}, we prove that either G is almost simple, or G is a primitive group of affine type. If further G is an almost simple primitive group, then, with two exceptions, the socle of G acts transitively on the edge set of {\varGamma}.

scholarly journals AUTOMORPHISM GROUPS OF QUANDLES

2012 ◽  
Vol 11 (01) ◽  
pp. 1250008 ◽  
Author(s):  
MOHAMED ELHAMDADI ◽  
JENNIFER MACQUARRIE ◽  
RICARDO RESTREPO
Keyword(s):  
Automorphism Group ◽  
Automorphism Groups ◽  
Affine Group ◽  
Low Dimensional Topology ◽  
Inner Automorphism ◽  
Mathematical Sciences ◽  
Low Dimensional

We prove that the automorphism group of the dihedral quandle with n elements is isomorphic to the affine group of the integers mod n, and also obtain the inner automorphism group of this quandle. In [B. Ho and S. Nelson, Matrices and finite quandles, Homology Homotopy Appl.7(1) (2005) 197–208.], automorphism groups of quandles (up to isomorphisms) of order less than or equal to 5 were given. With the help of the software Maple, we compute the inner and automorphism groups of all seventy three quandles of order six listed in the appendix of [S. Carter, S. Kamada and M. Saito, Surfaces in 4-Space, Encyclopaedia of Mathematical Sciences, Vol. 142, Low-Dimensional Topology, III (Springer-Verlag, Berlin, 2004)]. Since computations of automorphisms of quandles relate to the problem of classification of quandles, we also describe an algorithm implemented in C for computing all quandles (up to isomorphism) of order less than or equal to nine.

Automorphisms of prime-cube order group

2019 ◽  
Vol 11 (03) ◽  
pp. 1950032
Author(s):  
Yi Wang
Keyword(s):  
Automorphism Group ◽  
Automorphism Groups ◽  
Full Automorphism Group ◽  
Order Group ◽  
Transitive Graphs

A graph is called half-arc-transitive if its full automorphism group acts transitively on vertices and edges, but not on arcs. Let [Formula: see text] be a prime-cube order group. In this paper, we determined the structures of the automorphism groups of [Formula: see text], and the result is used to determine the classification of half-arc-transitive graphs of order [Formula: see text] with valency [Formula: see text].

scholarly journals Conjugacy and dynamics in almost automorphism groups of trees

2021 ◽  
pp. 1-49
Author(s):  
Gil Goffer ◽  
Waltraud Lederle
Keyword(s):  
Automorphism Group ◽  
Automorphism Groups ◽  
Conjugacy Problem ◽  
Conjugacy Classes ◽  
Homogeneous Tree ◽  
Regular Tree

We determine when two almost automorphisms of a regular tree are conjugate. This is done by combining the classification of conjugacy classes in the automorphism group of a level-homogeneous tree by Gawron, Nekrashevych and Sushchansky and the solution of the conjugacy problem in Thompson’s [Formula: see text] by Belk and Matucci. We also analyze the dynamics of a tree almost automorphism as a homeomorphism of the boundary of the tree.

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