Alexander Dranishnikov, Viktor Schroeder
We prove that a right angled Coxeter group with chromatic number n can be embedded in a bilipschitz way into the product of n locally finite trees. We give applications of this result to various embedding problems and determine the hyperbolic rank of products of exponentially branching trees.
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We prove that a finitely generated, right-angled, hyperbolic Coxeter group can be quasiisometrically embedded into the product of n binary trees, where n is the chromatic number of the group. As application we obtain certain strongly aperiodic tilings of the Davis complex of these groups.
In this article, given two finite simplicial graphs $Γ_1$ and $Γ_2$, we state and prove a complete description of the possible morphisms $C(Γ_1) \to C(Γ_2)$ between the right-angled Coxeter groups $C(Γ_1)$ and $C(Γ_2)$. As an application, assuming that $Γ_2$ is triangle-free, we show that, if $C(Γ_1)$ is isomorphic to a subgroup of $C(Γ_2)$, then the ball of radius $8|Γ_1||Γ_2|$ in $C(Γ_2)$ contains the basis of a subgroup isomorphic to $C(Γ_1)$. This provides an algorithm determining whether or not, among two given two-dimensional right-angled Coxeter groups, one is isomorphic to a subgroup o…
RAAGedy right-angled Coxeter groups II: in the quasiisometry class of the tree RAAGs
本文对拟等距于树 RAAG 的二维右角 Coxeter 群分类，证明满足条件的此类群含可见有限指数右角 Artin 子群，解决了特定拟等距类群的结构问题。
The purpose of this paper is to discuss the validity of the assumptions (W) and (S) stated in a previous work, about the torsion in the modular l-adic cohomology of Deligne-Lusztig varieties associated to Coxeter elements. We prove that both (W) and (S) hold except for groups of type E_7 or E_8.
Coxeter embeddings are injective
本文利用Coxeter剖分概念证明了Coxeter群在某些嵌入下的单射性，通过研究Lusztig剖分对最简单类型的剖分进行分类，并证明这些嵌入保持Coxeter数。
We study the cohomology with modular coefficients of Deligne-Lusztig varieties associated to Coxeter elements. Under some torsion-free assumption on the cohomology we derive several results on the principal l-block of a finite reductive group G(F_q) when the order of q modulo l is assumed to be the Coxeter number. These results include the determination of the planar embedded Brauer tree of the block (as conjectured by Hiss, Lübeck and Malle) and the derived equivalence predicted by the geometric version of Broué's conjecture.
To any finite graph $X$ (viewed as a topological space) we assosiate some explicit compact metric space ${\cal X}^r(X)$ which we call {\it the reflection tree of graphs $X$}. This space is of topological dimension $\le1$ and its connected components are locally connected. We show that if $X$ is appropriately triangulated (as a simplicial graph $Γ$ for which $X$ is the geometric realization) then the visual boundary $\partial_\infty(W,S)$ of the right angled Coxeter system $(W,S)$ with the nerve isomorphic to $Γ$ is homeomorphic to ${\cal X}^r(X)$. For each $X$, this yields in particular many w…
Bowditch's JSJ tree for splittings over 2-ended subgroups is a quasi-isometry invariant for 1-ended hyperbolic groups which are not cocompact Fuchsian. Our main result gives an explicit, computable "visual" construction of this tree for certain hyperbolic right-angled Coxeter groups. As an application of our construction we identify a large class of such groups for which the JSJ tree, and hence the visual boundary, is a complete quasi-isometry invariant, and thus the quasi-isometry problem is decidable. We also give a direct proof of the fact that among the Coxeter groups we consider, the coco…
Stabilizers in Coxeter groups with a transpositional action
本文研究以简单图Γ的线图为Coxeter图的单链Coxeter群的换位作用的点稳定子，证明其为有限指数反射子群并确定其Coxeter图，还建立了两类Coxeter群间的有限指数嵌入关系。
In this paper we exhibit two infinite families of trees $\{T^1_n\}_{n \geq 17}$ and $\{T^2_n\}_{n \geq 17}$ on $n$ vertices, such that $T^1_n$ and $T^2_n$ are non-isomorphic, co-spectral, and the right-angled Coxeter groups (RACGs) based on $T^1_n$ and $T^2_n$ have the same geodesic growth with respect to the standard generating set. We then show that the spectrum of a tree does is not sufficient to determine the geodesic growth of the RACG based on that tree, by providing two infinite families of trees $\{S^1_n\}_{n \geq 11}$ and $\{S^2_n\}_{n \geq 11}$, on $n$ vertices, such that $S^1_n$ and…
An odd Coxeter group $W$ is one which admits a Coxeter system $(W,S)$ for which all the exponents $m_{ij}$ are either odd or infinity. The paper investigates the family of odd Coxeter groups whose associated labeled graphs $\mathcal{V}_{(W,S)}$ are trees. It is known that two Coxeter groups in this family are isomorphic if and only if they admit Coxeter systems having the same rank and the same multiset of finite exponents. In particular, each group in this family is isomorphic to a group that admits a Coxeter system whose associated labeled graph is a star shaped tree. We give the complete de…
A group G has property FA if G fixes a point of every tree on which G acts without inversions. We prove that every Coxeter system of finite rank has a visual JSJ decomposition over subgroups with property FA. As an application, we reduce the twist conjecture to Coxeter systems that are indecomposable with respect to amalgamated products over visual subgroups with property FA.
Let W be an irreducible finitely generated Coxeter group. The geometric representation of W in GL(V) provides a discrete embedding in the orthogonal group of the Tits form (the associated bilinear form of the Coxeter group). If the Tits form of the Coxeter group is non-positive and non-degenerate, the Coxeter group does not contain any finite index subgroup isomorphic to an irreducible lattice in a semisimple group of R-rank greater or equal to 2.
We give explicit necessary and sufficient conditions for the abstract commensurability of certain families of 1-ended, hyperbolic groups, namely right-angled Coxeter groups defined by generalized theta-graphs and cycles of generalized theta-graphs, and geometric amalgams of free groups whose JSJ graphs are trees of diameter at most 4. We also show that if a geometric amalgam of free groups has JSJ graph a tree, then it is commensurable to a right-angled Coxeter group, and give an example of a geometric amalgam of free groups which is not quasi-isometric (hence not commensurable) to any group w…
Finite Coxeter Groups and Generalized Elnitsky Tilings
本文基于Elnitsky对A、B、D型Coxeter群约化词与多边形铺砌的双射，通过嵌入对称群的方法，将其推广至所有有限Coxeter群。
Representations of Coxeter groups over fusion rings and hyperplane complements
本文研究Coxeter群在融合环上的忠实实现及其Vinberg系统，证明其诱导超平面补集嵌入，从而为Artin–Tits群间的强可容许同态提供几何实现。
Let W be an irreducible, finitely generated Coxeter group. The geometric representation provides an discrete embedding in the orthogonal group of the so-called Tits form. One can look at the representation modulo the kernel of this form; we give a new proof of the following result of Vinberg: if W is non-affine, then this representation remains faithful. Our proof uses relative Kazhdan Property (T). The following corollary was only known to hold when the Tits form is non-degenerate: the reduced C*-algebra of W is simple with a unique normalized trace. Some other corollaries are pointed out.
Profinite properties of Coxeter groups
该研究证明考克斯特群在 Serre 意义下是“好”的，其树作用产生的分裂可被 profinite 完备化检测，还证明多族考克斯特群及部分类型考克斯特群的 profinite 刚性，并在附录中证明 Atiyah 猜想对考克斯特群成立及相关不变量性质。
The Bruhat Order of a Finite Coxeter Group and Elnitsky Tilings
本文证明有限Coxeter群中任意元素及其约化表达式对应一个2m-多边形的Elnitsky铺砌，其中m为子群指数，构造性证明结合E-嵌入与删除序，并给出E8等示例。
This paper introduces a new class of right-angled Coxeter groups with totally disconnected Morse boundaries. We construct this class recursively by examining how the Morse boundary of a right-angled Coxeter group changes if we glue a graph to its defining graph. More generally, we present a method to construct amalgamated free products of CAT(0) groups with totally disconnected Morse boundaries that act geometrically on CAT(0) spaces that have a treelike block decomposition.
A generic finite presentation defines a word hyperbolic group whose boundary is homeomorphic to the Menger curve. In this article, we produce the first known examples of non-hyperbolic $CAT(0)$ groups whose visual boundary is homeomorphic to the Menger curve. The examples in question are the Coxeter groups whose nerve is a complete graph on $n$ vertices for $n\geq 5$. The construction depends on a slight extension of Sierpiński's theorem on embedding $1$--dimensional planar compacta into the Sierpiński carpet. See the appendix for a brief erratum.
Bestvina metric and tree reduction for $K(π,1)$-conjecture
本文通过构造Artin群在Bestvina复形上的作用，将$K(π,1)$猜想简化为Coxeter图为树的Artin群性质，推导出新的满足该猜想的Artin群类别。
We characterise when there exists a quasiisometric embedding between two solvable Baumslag-Solitar groups. This extends the work of Farb and Mosher on quasiisometries between the same groups. More generally, we characterise when there can exist a quasiisometric embedding between two treebolic spaces. This allows us to determine when two treebolic spaces are quasiisometric, confirming a conjecture of Woess. The question of whether there exists a quasiisometric embedding between two treebolic spaces turns out to be equivalent to the question of whether there exists a bilipschitz embedding betwee…
From Trees to Tripods: Proof of $K(π,1)$ for Artin groups with $ABI$-type spherical parabolics
本文通过构造注入度量空间的塔，证明了具有特定球面抛物子群性质的Artin群满足K(π,1)猜想。
We introduce and study certain topological spaces associated with connected rooted graphs. These spaces reflect combinatorial and order theoretic properties of the underlying graph and relate in the case of hyperbolic graphs to Gromov's hyperbolic compactification. They are particularly tractable in the case of Cayley graphs of finite rank Coxeter groups. In that context we speak of the compactification and the boundary of the Coxeter group. As it turns out, the canonical action of the Coxeter group on its Cayley graph induces a natural action on the compactification and the boundary. From thi…
Quasi-Isometries for certain Right-Angled Coxeter Groups
本文针对有限展示、单端、二维直角考克斯特群，基于定义图构造柱面JSJ树，证明其二端边稳定子与定义图不含特定细分K4等价，并利用结构不变量给出由定义图决定的拟等距不变量，在无刚性顶点情形下进一步细化为完全拟等距不变量。
Embedding products of trees into higher rank
该研究通过纯几何方法，证明了n个双曲平面乘积到任意秩n非紧型对称空间的拟等距嵌入、n个3正则树乘积到特定秩n厚欧氏建筑的双李普希茨嵌入，拓展了Fisher-Whyte的既有结果，也适用于非布吕阿-蒂茨建筑。
Embedding relatively hyperbolic groups into products of binary trees
本文证明了具有拟阿贝尔边缘子群的相对双曲群可拟等距嵌入二叉树乘积，推广了双曲群的结果，并发展了 diaries 和 linear statistics 理论以将无穷度数树乘积的嵌入升级为二叉树乘积的嵌入。
Conformal dimension bounds for certain Coxeter group Bowditch boundaries
针对定义图为完全图且边标签≥3的Coxeter群，通过拟等距嵌入圆树和CAT(-1)空间的几何有限作用给出其Bowditch边界共形维数的上下界，揭示相关群族存在无限拟等距类并得到共形维数的稠密性结果。
We show that every graph product of finitely generated abelian groups acts properly and cocompactly on a CAT(0) cubical complex. The complex generalizes (up to subdivision) the Salvetti complex of a right-angled Artin group and the Coxeter complex of a right-angled Coxeter group. In the right-angled Artin group case it is related to the embedding into a right-angled Coxeter group described by Davis and Januszkiewicz. We compare the approaches and also adapt the argument that the action extends to finite index supergroup that is a graph product of finite groups.
Conformal dimension bounds, Pontryagin sphere boundaries, and algebraic fibering of right-angled Coxeter groups
研究直角考克斯特群，通过引入\((n,m)\) - 分支条件构造组合圆树并嵌入戴维斯复形，给出双曲群边界共形维数下界，展示相关图族，证明嵌入结果，得出群的共形维数等结论，升级相关工作。
Hilbert transforms on Coxeter groups and groups acting on buildings
本文通过几何对象建立新模型，证明Coxeter群及作用于建筑的群上Hilbert变换满足Cotlar恒等式，从而得到$L_p$-有界性，并首次在具有性质(F$\mathbb{R}$)的群上实现该结果。
A Topological Embedding of the Binary Tree into the Square Lattice
该研究证明最大度为3的n顶点有限树可拓扑嵌入整数格点Z²且像顶点数不超7/3 n，以更优常数重现Valiant相关结果的弱形式，还解答了已有文献中的问题，给出无正则映射但粗布线轮廓线性增长的图对示例。
We prove that numerous negatively curved simply connected locally compact polyhedral complexes, admitting a discrete cocompact group of automorphisms, have automorphism groups which are locally compact, uncountable, non linear and virtually simple. Examples include hyperbolic buildings, Cayley graphs of word hyperbolic Coxeter systems, and generalizations of cubical complexes, that we call even polyhedral complexes. We use tools introduced by Tits in the case of automorphism groups of trees, and Davis-Moussong's geometric realisation of Coxeter systems.
We show that trees of manifolds, the topological spaces introduced by Jakobsche, appear as boundaries at infinity of various spaces and groups. In particular, they appear as Gromov boundaries of some hyperbolic groups, of arbitrary dimension, obtained by the procedure of strict hyperbolization. We also recognize these spaces as boundaries of arbitrary Coxeter groups with manifold nerves, and as Gromov boundaries of the fundamental groups of singular spaces obtained from some finite volume hyperbolic manifolds by cutting off their cusps and collapsing the resulting boundary tori to points.
We study isometric actions of tree automorphism groups on the infinite-dimensional hyperbolic spaces. On the one hand, we exhibit a general one-parameter family of such representations and analyse the corresponding equivariant embeddings of the trees, showing that they are convex-cocompact and asymptotically isometric. On the other hand, focusing on the case of sufficiently transitive groups of automorphisms of locally finite trees, we classify completely all irreducible representations by isometries of hyperbolic spaces. It turns out that in this case our one-parameter family exhausts all non…
We prove the equivalence between a relative bottleneck property and being quasi-isometric to a tree-graded space. As a consequence, we deduce that the quasi-trees of spaces defined axiomatically by Bestvina-Bromberg-Fujiwara are quasi-isometric to tree-graded spaces. Using this we prove that mapping class groups quasi-isometrically embed into a finite product of simplicial trees. In particular, these groups have finite Assouad-Nagata dimension, direct embeddings exhibiting $\ell^p$ compression exponent $1$ for all $p\geq 1$ and they quasi-isometrically embed into $\ell^1(\mathbb N)$. We deduce…
Coarse embeddings of products of trees as quasi-isometry invariants
研究茂密树乘积能粗嵌入到多种群中的最大因子数，利用此区分相关群并排除粗嵌入，基于树乘积到分层双曲空间的粗嵌入一般陈述得出这些应用。
Coset geometries acting on their elements: The $j$-diagonals twisting
该研究针对陪集关联系统定义$j$-对角线扭曲构造，证明对应正则超图的存在性，还定义结合Coxeter图的扩张运算，可还原正则多面体的相关扭曲扩张。
Uniquely labelled geodesics of Coxeter groups
本文提出唯一标记测地线（u.l.g.）概念，在有限 Coxeter 群中借助生成函数精确计数，并推广至无限 Coxeter 群，证明有限分支指数下长度有限，且以 $\widetilde{D}_6$ 为例展示无限 u.l.g. 的存在及其几何关系。
Using suitable deformations of simplicial trees and the duality theory for median sets, we show that every free action on a median set can be extended to a free and transitive one. We also prove that the category of median groups is a reflective full subcategory of the category of free actions on pointed median sets.
We say a permutation $π=π_1π_2\cdotsπ_n$ in the symmetric group $\mathfrak{S}_n$ has a peak at index $i$ if $π_{i-1}<π_i>π_{i+1}$ and we let $P(π)=\{i \in \{1, 2, \ldots, n\} \, \vert \, \mbox{$i$ is a peak of $π$}\}$. Given a set $S$ of positive integers, we let $P (S; n)$ denote the subset of $\mathfrak{S}_n$ consisting of all permutations $π$, where $P(π) =S$. In 2013, Billey, Burdzy, and Sagan proved $|P(S;n)| = p(n)2^{n-\lvert S\rvert-1}$, where $p(n)$ is a polynomial of degree $\max(S)- 1$. In 2014, Castro-Velez et al. considered the Coxeter group of type $B_n$ as the group of signed per…
Embedding Higman-Thompson groups of unfolding trees into the Leavitt path algebras
本文将有向图展开树的Higman-Thompson群嵌入Leavitt路代数，并证明有根Leavitt路代数的同构可诱导这些群之间的同构。
Simple Lattices in Products of Davis Complexes
本文研究了在特定Davis复形积中构造简单一致晶格的方法，引入了Burger-Mozes通用群的类比，并提供了一个局部标准来判断顶点传递群在通用群中的稠密性。
We show that a relatively hyperbolic group quasi-isometrically embeds in a product of finitely many trees if the peripheral subgroups do, and we provide an estimate on the minimal number of trees needed. Applying our result to the case of 3-manifolds, we show that fundamental groups of closed 3-manifolds have linearly controlled asymptotic dimension at most 8. To complement this result, we observe that fundamental groups of Haken 3-manifolds with non-empty boundary have asymptotic dimension 2.
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