Connectivity of the coset poset and the subgroup poset of a group

On families of nilpotent subgroups and associated coset posets

We study some properties of the coset poset associated with the family of subgroups of class $\leq 2$ of a nilpotent group of class $\leq 3$. We prove that under certain assumptions on the group the coset poset is simply-connected if and only if the group is $2$-Engel, and $2$-connected if and only if the group is nilpotent of class $2$ or less. We determine the homotopy type of the coset poset for the group of $4\times 4$ upper unitriangular matrices over $\mathbb{F}_p$, and for the Burnside groups of exponent $3$.

Connectivity of the coset poset

Topological concepts may be applied to any poset via the simplicial complex of finite chains. The coset poset C(G) of a finite group G (consisting of all cosets of all proper subgroups of G, ordered by inclusion) was introduced by Kenneth S. Brown in his study of the probabilistic zeta function P(G,s), and Brown's results motivate the study of the homotopy type of C(G). After a detailed introduction to basic simplicial topology and homotopy theory for finite posets (Chapter 2), we examine the connectivity of the coset poset (Chapter 3). Of particular interest is the fundamental group, and we p…

有限单群的不变生成与陪集偏序集的有理同调

Invariable generation of finite simple groups and rational homology of coset posets

本文证明每个有限单群都可由一个西洛子群与一个循环群不变生成，并据此推出任意有限群的陪集偏序集阶复形具有非平凡约化有理同调。

Spherical posets from commuting elements

In this paper we study the homotopy type of the partially ordered set of left cosets of abelian subgroups in an extraspecial $p$-group. We prove that the universal cover of its nerve is homotopy equivalent to a wedge of $r$-spheres where $2r \geq 4$ is the rank of its Frattini quotient. This determines the homotopy type of the universal cover of the classifying space of transitionally commutative bundles.

Higher generation by abelian subgroups in Lie groups

To a compact Lie group $G$ one can associate a space $E(2,G)$ akin to the poset of cosets of abelian subgroups of a discrete group. The space $E(2,G)$ was introduced by Adem, F. Cohen and Torres-Giese, and subsequently studied by Adem and Gómez, and other authors. In this short note, we prove that $G$ is abelian if and only if $π_i(E(2,G))=0$ for $i=1,2,4$. This is a Lie group analogue of the fact that the poset of cosets of abelian subgroups of a discrete group is simply--connected if and only if the group is abelian.

几何可定向3-流形群的交换性分类空间

The classifying space for commutativity of geometric orientable 3-manifold groups

本文研究无限离散群的万有过渡交换主丛全空间，证明闭可定向几何3-流形基本群的该空间总是同伦等价于圆环楔和，并建立了相关同伦型结构结果。