Twisted conjugacy classes of the unit element

We study twisted conjugacy classes of the unit element in different groups. Fel’shtyn and Troitsky showed that the twisted conjugacy class of the unit element of an abelian group is a subgroup for every automorphism. The structure is investigated of a group whose twisted conjugacy class of the unit element is a subgroup for every automorphism (inner automorphism).     

On spherical twisted conjugacy classes

Let G be a simple algebraic group over an algebraically closed field of good odd characteristic, and let ?? be an automorphism of G arising from an involution of its Dynkin diagram. We show that the spherical ??-twisted conjugacy classes are precisely those intersecting only Bruhat cells corresponding to twisted involutions in the Weyl group. We show how the analogue of this statement fails in the triality case. As a byproduct, we obtain a dimension formula for spherical twisted conjugacy classes that was originally obtained by J.-H. Lu in characteristic zero.     

Nielsen Zeta Function, 3-Manifolds, and Asymptotic Expansions in the Nielsen Theory

We prove that the Nielsen zeta function is either a rational function or a radical of a rational function for orientation-preserving homeomorphisms of closed orientable 3-dimensional manifolds which are special Haken or Seifert manifolds. In the case of a pseudo-Anosov homeomorphism of a surface, we find an asymptotics for the number of twisted conjugacy classes or for the number of Nielsen fixed-point classes with norm at most x. Bibliography: 20 titles.     

Minimal length elements in some double cosets of Coxeter groups

We study the minimal length elements in some double cosets of Coxeter groups and use them to study Lusztig's G-stable pieces and the generalization of G-stable pieces introduced by Lu and Yakimov. We also use them to study the minimal length elements in a conjugacy class of a finite Coxeter group and prove a conjecture in [M. Geck, S. Kim, G. Pfeiffer, Minimal length elements in twisted conjugacy classes of finite Coxeter groups, J. Algebra 229 (2) (2000) 570-600].     

A module-theoretic approach to Clifford theory for blocks

This work concerns a generalization of Clifford theory to blocks of group-graded algebras. A module-theoretic approach is taken to prove a one-to-one correspondence between the blocks of a fully group-graded algebra covering a given block of its identity component, and conjugacy classes of blocks of a twisted group algebra. In particular, this applies to blocks of a finite group covering blocks of a normal subgroup.

     

CARTAN DECOMPOSITION FOR COMPLEX LOOP GROUPS

In this note we formulate and prove a version of Cartan decomposition for holomorphic loop groups, similar to Cartan decomposition for p-adic loop groups, discussed in [3], [6]. The main technical tool that we use is the (well-known) interpretation of twisted conjugacy classes in the holomorphic loop group in terms of principal holomorphic bundles on an elliptic curve.     

Using Mathematica to compute conjugacy classes

The conjugacy classes of finite groups play an important role in the representation theory of those groups, and it is useful to be able to compute the conjugacy classes quickly. A procedure is developed and then implemented with Mathematica to discover these conjugacy classes. The computations make use of the Cayley table in its regular form for the group. The conjugacy classes for C_4v, the point symmetry group of the square, are displayed.     

Products of conjugacy classes in Chevalley groups I. Extended covering numbers

This paper is concerned with products of conjugacy classes in Chevalley groups. We prove that in any quasisimple Chevalley groupG proper or twisted, over any field, the extended covering number is bounded above linearly in terms of the rank ofG, that is, for some constante, for any Chevalley groupG, the product of anye · rank(G) non-central classes covers all ofG. We give estimates for the constante in different cases. The authors gratefully acknowledge the support of EPSRC through a Visiting Fellowship number GR/M58542 and a Research grant number GR/L92174.     

Dimension formula of cusp form spaces on half-spaces of quaternions

A dimension formula for the spaces of cusp forms defined on quatemionic half-spacea of degree two is obtained by Selberg trace formula, and the contributions of some conjugacy classes are calculated. Some results on the classification of the conjugacy classes of modular group are obtained.     

Parity features for classes of the infinite symmetric group

A conjugacy class in the infinite-symmetric group is said to have parity features if no finitary odd permutation is a product of two of its members. The conjugacy classes having parity features are determined. The role played by a property of this kind in determining products of conjugacy classes in any group in which every element is conjugate with its inverse is studied.     

Conjugacy Length in Group Extensions

Determining the length of short conjugators in a group can be considered as an effective version of the conjugacy problem. The conjugacy length function provides a measure for these lengths. We study the behavior of conjugacy length functions under group extensions, introducing the twisted and restricted conjugacy length functions. We apply these results to show that certain abelian-by-cyclic groups have linear conjugacy length function and certain semidirect products ?^d ? ?^k have at most exponential (if k > 1) or linear (if k = 1) conjugacy length functions.     

On the existence of ternary quasi-groups with two or eight conjugacy classes

The existence of 3-quasi-groups with two and eight conjugacy classes is investigated and several infinite classes of orders of such quasi-groups are found. New 3-quasi-groups are constructed from sets of quasi-groups derived from Steiner quadruple systems. These derived quasi-groups are altered so as to destroy certain identities satisfied by the 3-quasi-group originally associated with the quadruple system. Only the appropriate identities for the required number of conjugacy classes remain satisfied by these reconstructed 3-quasi-groups.     

论有限群元素共轭类的平均长度

本文研究有限群元素共轭类的平均长度问题.利用初等群论方法和有限群特征标理论,在共轭类平均长度为某一定数时,获得了对有限群结构的刻划,且对有限群数量性质的研究是有意义的.