仿射Weyl群上的Demazur乘积

Demazure乘积是定义在一般Coxeter群上的一类幺半群乘积.它自然地出现在李理论中的不同领域中.本文将研究仿射Weyl群上Demazur乘积.我们的主要结果是发现了它与有限Weyl群上的量子Bruhat图之间的一个紧密联系.作为应用,我们给出了仿射Weyl群最低双边胞腔元素之间Demazure乘积的显示表达式,并得到了最低双边胞腔元素的一般牛顿点以及Lusztig-Vogan映射的具体刻画.     

一类对称群的胞腔

胞腔理论是Kazhdan-Lusztig理论中的核心理论之一,它对Coxeter群以及Hecke代数的表示起着重要作用.本文借助Matlab软件,对于对称群中的任意一个置换,可以很快得出其所对应的标准Young表;其次,借助程序,得到了在一定情形下,一类对称群所对应的双边胞腔、右(左)胞腔的个数.     

加权的Coxeter群C_n的左胞腔(英文)

仿射Weyl群(C_n,S)可以看做仿射Weyl群(A_m,S_m)(其中m∈{2n-1,2n,2n+1})在其某个群自同构α下的固定点集合.A_m上的长度函数l_m可以看作C_n上的一个权函数.因此通过对仿射Weyl群(A_m,S_m)在其群自同构α下的固定点集合的研究可以得出加权的Coxeter群(C_n,l_m)的性质.本文给出了加权的Coxeter群(C_n,l_(2n))对应于划分42~(n-2)1的所有胞腔的清晰刻画.     

Kazhdan-Lusztig理论:起源、发展、影响和一些待解决的问题

Kazhdan-Lusztig理论是代数群表示论近40年来最重要的发展之一.该理论在很多重要问题的解决上起关键作用,如有限Lie型群的不可约特征标的分类和Lie理论中某些不可约表示的特征标的确定等.同时该理论开创了很多有活力的研究课题,如Kazhdan-Lusztig多项式的研究、Coxeter群的胞腔的研究及Coxeter群与相交上同调和K理论的联系等.本文将简要介绍这一理论的起源、发展、影响和一些未解决的问题.     

带权的Coxeter群(_n,l_(2n))的左胞腔（英文）

仿射Weyl群五_(2n)在某个群自同构下的固定点集合可以看作仿射Weyl群_n.因此通过研究_(2n)在这个群自同构下的固定点集合,可以得出加权的Coxeter群_n中划分32~(n-1)对应的所有胞腔的清晰刻画.     

万花筒型散射的杨-Baxter方程组

本文以根图及Weyl分类的B_n与D_n万花筒型散射所满足的杨-Baxter方程组,并证明它们在Coxeter 图端点具有反射行为,也讨论了它们的物理意义。     

扭型Kazhdan-Lusztig理论中的逆反多项式

本文研究扭型Kazhdan-Lusztig多项式的逆反多项式的性质及其计算方法.构造了Lusztig对偶模M的一类特异基(或D-基),获得了Hecke代数在此基上的作用公式.在有限Coxeter群情形下,获得了Lusztig-Vogan模的结构常数的关系.     

关于E型群高次层上同调群的一个零化性质

令 G 是特征数 p>0 的代数闭域上的单连通半单线性代数群.设 p≥h-1 (h 是 G 的根系的 Coxeter 数),ρ 是正根之和半.[1]证明:若λ=0 或 λ 是“强支配权”,则对所有 i>0 有H~i(G/B,S~n(u~*)(?)λ)=0,式中u~*=(LieU)~*,U 是 G 的 Borel 子群 B 的幺幂根基.特别,当 G 是 A,B,C 或 D 型群时,上述零化性质对所有 λ∈-ρ+X(T)_+ 成立.本文证明了:当 G 是 E_6 型群时,上述零化性质对所有 λ∈-ρ+X(T)_+ 成立.当 G 是 E_7 或 E_8 型群时,我们也在比“强支配权”弱的条件下得到了如上零化性质.     

4p阶3度点传递图

一个图称为点传递图,如果它的全自同构群在它的顶点集合上作用传递.证明了一个4p(p为素数)阶连通3度点传递图或者是Cayley图,或者同构于下列之一;广义Petersen图P(10,2),正十二面体,Coxeter图,或广义Petersen图P(2p,k),这里k2≡-1(mod 2p).     

子群的核平凡或正规闭包极大的有限p群

称有限p群G为ACT群,如果对每个交换子群H,其正规核HG=1或HG=H.又称p群G是CC群,如果对每个非正规交换子群H,有HG=1或HG在G中的指数为p.本文分类了ACT群和CC群.     

Reflection Independence in Even Coxeter Groups

If (W,S) is a Coxeter system, then an element of W is a reflection if it is conjugate to some element of S. To each Coxeter system there is an associated Coxeter diagram. A Coxeter system is called reflection preserving if every automorphism of W preserves reflections in this Coxeter system. As a direct application of our main theorem, we classify all reflection preserving even Coxeter systems. More generally, if (W,S) is an even Coxeter system, we give a combinatorial condition on the diagram for (W,S) that determines whether or not two even systems for W have the same set of reflections. If (W,S) is even and (W,S) is not even, then these systems do not have the same set of reflections. A Coxeter group is said to be reflection independent if any two Coxeter systems (W,S) and (W,S) have the same set of reflections. We classify all reflection independent even Coxeter groups.Mathematics Subject Classifications (2000). 20F05, 20F55, 20F65, 51F15.     

On the Derived Length of Coxeter Groups

We characterize certain properties of the derived series of Coxeter groups by properties of the corresponding Coxeter graphs. In particular, we give necessary and sufficient conditions for a Coxeter group to be quasiperfect.     

A complex for right-angled Coxeter groups

We associate to each right-angled Coxeter group a 2-dimensional complex. Using this complex, we show that if the presentation graph of the group is planar, then the group has a subgroup of finite index which is a 3-manifold group (that is, the group is virtually a 3-manifold group). We also give an example of a right-angled Coxeter group which is not virtually a 3-manifold group.

     

Spherical coxeter groups and hyperelliptic 3-manifolds

Reflection groups of Coxeter polyhedra in three-dimensional Thurston geometries are examined. For a wide class of Coxeter groups, the existence of subgroups of finite index that uniformize hyperelliptic 3-manifolds is established. Translated fromMatematicheskie Zametki, Vol. 66, No. 2, pp. 173–177, August, 1999.     

An Adjacency Criterion for Coxeter Matroids

A Coxeter matroid is a generalization of matroid, ordinary matroid being the case corresponding to the family of Coxeter groups A _n , which are isomorphic to the symmetric groups. A basic result in the subject is a geometric characterization of Coxeter matroid in terms of the matroid polytope, a result first stated by Gelfand and Serganova. This paper concerns properties of the matroid polytope. In particular, a criterion is given for adjacency of vertices in the matroid polytope.     

On Subgroup Separability in Hyperbolic Coxeter Groups

We prove that certain hyperbolic Coxeter groups are separable on their geometrically finite subgroups.     

Alternating subgroups of Coxeter groups

We study combinatorial properties of the alternating subgroup of a Coxeter group, using a presentation of it due to Bourbaki.     

Commensurability classification of a family of right-angled Coxeter groups

We classify the members of an infinite family of right-angled Coxeter groups up to abstract commensurability.

     

Representation type of 0-Hecke algebras

In the present paper we determine the representation type of the 0-Hecke algebra of a finite Coxeter group.