Tadeusz Januszkiewicz, Jacek Swiatkowski
We define graph products of families of pairs of groups and study the question when two such graph products are commensurable. As an application we prove linearity of certain graph products.
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We initiate the study of the $p$-local commensurability graph of a group, where $p$ is a prime. This graph has vertices consisting of all finite-index subgroups of a group, where an edge is drawn between $A$ and $B$ if $[A : A\cap B]$ and $[B: A\cap B]$ are both powers of $p$. We show that any component of the $p$-local commensurability graph of a group with all nilpotent finite quotients is complete. Further, this topological criterion characterizes such groups. In contrast to this result, we show that for any prime $p$ the $p$-local commensurability graph of any large group (e.g. a nonabelia…
The commensurability index between two subgroups $A, B$ of a group $G$ is $[A : A \cap B] [B : A\cap B]$. This gives a notion of distance amongst finite-index subgroups of $G$, which is encoded in the p-local commensurability graphs of $G$. We show that for any metabelian group, any component of the $p$-local commensurabilty graph of $G$ has diameter bounded above by 4. However, no universal upper bound on diameters of components exists for the class of finite solvable groups. In the appendix we give a complete classification of components for upper triangular matrix groups in $\text{GL}(2, \m…
Suppose a group $G$ is quasi-isometric to a free product of a finite set $S$ of finitely generated abelian groups; let $S'$ denote the set of ranks of the free abelian parts of the groups in $S$. Then $G$ is commensurable with the free product of $\Z$ with a $\Z^n$ for each $n$ occurring in $S'$.
On the proofs of Leighton's Graph Covering Theorem, a notion dual to commensurability, and normal virtual retracts
本文通过反例说明Leighton定理的树格证明不充分，给出可公度化由共可公度化诱导的充要条件，并证明正规虚拟收缩子是虚拟直和项，回答Merladet和Minasyan的问题。
We define and discuss a notion called fibered commensurability of outer automorphisms of free groups. This notion lets us study symmetry of outer automorphisms. The notion of fibered commensurability is first defined by Calegari-Sun-Wang on mapping class groups. The Nielsen-Thurston type of mapping classes is a commensurability invariant. One of the important facts of fibered commensurability on mapping class groups is for the case of pseudo-Anosovs, there is a unique minimal element in each fibered commensurability class. For outer automorphisms, we first show that being atoroidal and fully i…
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…
We study to what extent torsion-free (Gromov)-hyperbolic groups are elementarily equivalent to their finite index subgroups. In particular, we prove that a hyperbolic limit group either is a free product of cyclic groups and surface groups, or admits infinitely many subgroups of finite index which are pairwise non elementarily equivalent.
Commensurability of lattices in right-angled buildings
本文证明均匀格子与图积弱可公度等价于其凸子群可分离，并推论特殊立方复形有共同有限覆盖，还推广至Coxeter群、Artin群及Fuchsian建筑的拟等距刚性。
We show that two uniform lattices of a regular right-angled Fuchsian building are commensurable, provided the chamber is a polygon with at least six edges. We show that in an arbitrary Gromov-hyperbolic regular right-angled building associated to a graph product of finite groups, a uniform lattice is commensurable with the graph product provided all of its quasiconvex subgroups are separable. We obtain a similar result for uniform lattices of the Davis complex of Gromov-hyperbolic two-dimensional Coxeter groups. We also prove that every extension of a uniform lattice of a CAT(0) square complex…
Commensurability and quasi-isometry classification for one vertex one loop tubular groups
本文对单顶点单环管状群按边映射交数分类：非零交数时全体可公度且拟等距；零交数时有两个拟等距类和无穷可公度类，两类间不拟等距。
Automorphisms of Bestvina-Brady Groups: IA Rigidity, Arithmetic Commensurability, and Finiteness
本文研究了Bestvina-Brady群的自同构性质，证明了IA刚性、算术共轭性和有限性相关结论，并探讨了其外自同构群的有限性。
Virtual inheritance properties of graph products
本文证明多种虚拟性质在图积下封闭，包括虚拟RFRS、虚拟（紧）特殊、虚拟CAT(0)立方体及虚拟正规多自由，并通过初等证明简化了Januszkiewicz和Świątkowski的强可公度定理。
Flat braid groups, right-angled Artin groups, and commensurability
本文研究了平坦辫群与直角Artin群的可公度性，证明了对于 $n=7$ 或 $\geq 11$ 时 $\mathrm{PFB}_n$ 并非实质上的直角Artin群，推翻了相关猜想，并发现 $\mathrm{FB}_7$ 与 $A(P_4)$ 可公度。
Let $G$ be a right-angled Artin group with defining graph $Γ$ and let $H$ be a finitely generated group quasi-isometric to $G(Γ)$. We show if $G$ satisfies (1) its outer automorphism group is finite; (2) $Γ$ does not have induced 4-cycle; (3) $Γ$ is star-rigid; then $H$ is commensurable to $G$. We show condition (2) is sharp in the sense that if $Γ$ contains an induced 4-cycle, then there exists an $H$ quasi-isometric to $G(Γ)$ but not commensurable to $G(Γ)$. Moreover, one can drop condition (1) if $H$ is a uniform lattice acting on the universal cover of the Salvetti complex of $G(Γ)$. As a …
Two groups have a common model geometry if they act properly and cocompactly by isometries on the same proper geodesic metric space. The Milnor-Schwarz lemma implies that groups with a common model geometry are quasi-isometric; however, the converse is false in general. We consider free products of uniform lattices in isometry groups of rank-1 symmetric spaces and prove, within each quasi-isometry class, residually finite groups that have a common model geometry are abstractly commensurable. Our result gives the first examples of hyperbolic groups that are quasi-isometric but do not virtually …
A BMW group of degree $(m,n)$ is a group that acts simply transitively on vertices of the product of two regular trees of degrees $m$ and $n$. We show that the number of commensurability classes of BMW groups of degree $(m,n)$ is bounded between $(mn)^{αmn}$ and $(mn)^{βmn}$ for some $0<α<β$. In fact, we show that the same bounds hold for virtually simple BMW groups. We introduce a random model for BMW groups of degree $(m,n)$ and show that asymptotically almost surely a random BMW group in this model is irreducible and hereditarily just-infinite.
We establish a general criterion for the finite presentability of subdirect products of groups and use this to characterize finitely presented residually free groups. We prove that, for all $n\in\mathbb{N}$, a residually free group is of type ${\rm{FP}}_n$ if and only if it is of type ${\rm{F}}_n$. New families of subdirect products of free groups are constructed, including the first examples of finitely presented subgroups that are neither ${\rm{FP}}_\infty$ nor of Stallings-Bieri type. The template for these examples leads to a more constructive characterization of finitely presented residua…
Rigidity and classification results for large-type Artin groups
本文计算了许多大类型Artin群交集图的自同构群，并以此为应用推导出包括外自同构群、可公度性分类及拟等距、测度等价、轨道等价、格嵌入和交叉积von Neumann代数刚性等一系列分类与刚性结果。
Graphically discrete groups and rigidity
本文引入群的图离散性概念，证明顶点群为图离散群的群图具强刚性，包括自由积的作用刚性与特定双曲群图的拟等距刚性，还给出例子并指出其非可公度不变性。
We prove that the topological full group $[[X]]$ of a two-sided full shift $X = Σ^{\mathbb{Z}}$ contains every right-angled Artin group (also called a graph group). More generally, we show that the family of subgroups with "linear look-ahead" is closed under graph products. We show that the lamplighter group $\mathbb{Z}_2 \wr \mathbb{Z}$ embeds in $[[X]]$, and conjecture that it does not embed in $[[X]]$ with linear look-ahead. Generalizing the lamplighter group, we show that whenever $G$ acts with "unique moves" (or at least "move-$A$ithfully"), we have $A \wr G \leq [[X]]$ for finite abelian…
We obtain a complete classification of graph products of finite abelian groups whose Cayley graphs with respect to the standard presentations are planar.
We prove that graph products of sofic groups are sofic, as are graphs of groups for which vertex groups are sofic and edge groups are amenable.
We study $(G,2)$-arc-transitive graphs for innately transitive permutation groups $G$ such that $G$ can be embedded into a wreath product $\symΓ\wr\sy\ell$ acting in product action on $Γ^\ell$. We find two such connected graphs: the first is Sylvester's double six graph with 36 vertices, while the second is a graph with $120^2$ vertices whose automorphism group is $\aut\sp 44$. We prove that under certain conditions no more such graphs exist.
We describe an underlying right angled building structure of any graph product of buildings. We describe the automorphism group of the graph product of buildings. We show that the notion of generalized graph product of a collection of groups, each with an action on a building, corresponds to the group of automorphisms generated via lifts. It follows that if each building is finite, then the generalized graph product is residually finite.
Residual Finiteness of Graph Wreath Products
本文研究了图圈积的剩余有限性问题，证明了其充要条件，并推广了置换圈积和自由积情形的已知结果。
We study coherence of graph products and Coxeter groups and obtain many results in this direction.
We show that the automorphism group of a graph product of finite groups $Aut(G_Γ)$ has Kazhdan's property (T) if and only if $Γ$ is a complete graph.
A notion of \emph{graph-wreath product} is introduced. We obtain sufficient conditions for these products to satisfy the topologically inspired finiteness condition type $\operatorname{F}_n$. Under various additional assumptions we show that these conditions are necessary. Our results generalise results of Cornulier about wreath products in case $n=2$. Graph-wreath products include classical permutational wreath products and semidirect products of right-angled Artin groups by groups of automorphisms amongst others.
Graph products of residually finite monoids are residually finite
本文证明了剩余有限幺半群的图积是剩余有限的，并得出其自由积及半群图积的相应结论。
We prove that the class of residually C groups is closed under taking graph products, provided that C is closed under taking subgroups, finite direct products and that free-by-C groups are residually C. As a consequence, we show that local embeddability into various classes of groups is stable under graph products. In particular, we prove that graph products of residually amenable groups are residually amenable, and that locally embeddable into amenable groups are closed under taking graph products.
Given a finite simplicial graph $Γ=(V,E)$ with a vertex-labelling $φ:V\rightarrow\left\{\text{non-trivial finitely generated groups}\right\}$, the graph product $G_Γ$ is the free product of the vertex groups $φ(v)$ with added relations that imply elements of adjacent vertex groups commute. For a quasi-isometric invariant $\mathcal{P}$, we are interested in understanding under which combinatorial conditions on the graph $Γ$ the graph product $G_Γ$ has property $\mathcal{P}$. In this article our emphasis is on number of ends of a graph product $G_Γ$. In particular, we obtain a complete character…
Weak amenability of discrete groups was introduced by Haagerup and co-authors in the 1980's. It is an approximation property known to be stable under direct products and free products. In this paper we show that graph products of weakly amenable discrete groups are weakly amenable (with Cowling-Haagerup constant 1). Along the way we construct a wall space associated to the word length structure of a graph product and also give a method for extending completely bounded functions on discrete groups to a completely bounded function on their graph product.
In this paper, we generalise Magnus' Freiheitssatz and solution to the word problem for one-relator groups by considering one relator quotients of certain classes of right-angled Artin groups and graph products of locally indicable polycyclic groups.
The goal of the paper "A new graph over semi-direct products of groups" is to define a graph Γ(G) on a group G when G splits over a normal subgroup. We demonstrate herein that the graph is ill-defined. We also attempt to ascertain causes for the discrepancies.
We show that $\mathcal{U}(\mathbb{Z}G)$, the unit group of the integral group ring $\mathbb{Z} G$, either satisfies Kazhdan's property (T) or is, up to commensurability, a non-trivial amalgamated product, in case $G$ is a finite group satisfying some mild conditions. Crucial in the proof is the construction of amalgamated decompositions of the elementary group $\operatorname{E}_2(\mathcal{O})$, where $\mathcal{O}$ is an order in a rational division algebra. A major step is to introduce subgroups $\operatorname{E}_2(Γ_n(\mathbb{Z}))$ inside the so-called higher modular groups $\operatorname{SL}…
Wreath products in the automorphism group of a full shift
本文证明，若非平凡全转移的自同构群子群H在有限支撑点上具有自由轨道，则对任意有限生成阿贝尔群A，抽象群A≀H可嵌入自同构群，并给出Z≀Z等新嵌入实例。
On the Isomorphism Problem of Cayley Graphs of Graph Products
该研究探讨图乘积的Cayley图同构问题，证明顶点群的Cayley图同构可推出对应图乘积的Cayley图同构，为相关同构判定提供理论依据。
Inspired by the definition of generalized wreath product of permutation groups, we define the generalized wreath product of graphs, containing the classical Cartesian and wreath product of graphs as particular cases. We prove that the generalized wreath product of Cayley graphs of finite groups is the Cayley graph of the generalized wreath product of the corresponding groups.
A graph product kernel means the kernel of the natural surjection from a graph product to the corresponding direct product. We prove that a graph product kernel of countable groups is special, and a graph product of finite or cyclic groups is virtually cocompact special in the sense of Haglund and Wise. The proof of this yields conditions for a graph over which the graph product of arbitrary nontrivial groups (or some cyclic groups, or some finite groups) contains a hyperbolic surface group. In particular, the graph product of arbitrary nontrivial groups over a cycle of length at least five, o…
We prove that the rapid decay property (RD) of groups is preserved by graph products defined on finite simplicial graphs.
Beyond graph products and cactus groups: quandle products of groups
提出群的quandle积以统一图积、仙人掌群、圈积和trickle群，并通过拟中值Cayley图的几何性质分析其结构。
We compute: * the cohomology with group ring coefficients of Artin groups (or actually, of their associated Salvetti complexes), Bestvina-Brady groups, and graph products of groups, * the L^2-Betti numbers of Bestvina-Brady groups and of graph products of groups, * the weighted L^2-Betti numbers of graph products of Coxeter groups. In the case of arbitrary graph products there is an additional proviso: either all factors are infinite or all are finite.(However, for graph products of Coxeter groups this proviso is unnecessary.)
We prove the exponential growth of product replacement graphs for a large class of groups. Much of our effort is dedicated to the study of product replacement graphs of Grigorchuk groups, where the problem is most difficult.
In this paper, we discuss the structural information about 2-arc-transitive (non-bipartite and bipartite) graphs of product action type. It is proved that a 2-arc-transitive graph of product action type requires certain restrictions on either the vertex-stabilizers or the valency. Based on the existence of some equidistant linear codes, a construction is given for 2-arc-transitive graphs of non-diagonal product action type, which produces several families of such graphs. Besides, a nontrivial construction is given for 2-arc-transitive bipartite graphs of diagonal product action type
Graph products and measure equivalence: classification, rigidity, and quantitative aspects
本文从测度群论视角研究群的图乘积，建立其测度等价分类定理及定量版本，推导冯·诺依曼代数结构，解决直角阿廷群的定量轨道等价逆问题，还构造了测度等价刚性但拟等距不刚性的群的首个例子。
Hilbert--Schmidt stability for graph products
本文证明了在弦图上阿贝尔群和C*-代数的图积具有希尔伯特-施密特稳定性，并展示了右角艺术群在此类稳定性下的结果。
The power graph $P(G)$ of a finite group $G$ is the graph with vertex set $G$ and two distinct vertices are adjacent if either of them is a power of the other. Here we show that the power graph $P(G_1 \times G_2)$ of the direct product of two groups $G_1$ and $G_2$ is not isomorphic to either of the direct, cartesian and normal product of their power graphs $P(G_1)$ and $P(G_2)$. A new product of graphs, namely generalized product, has been introduced and we prove that the power graph $P(G_1 \times G_2)$ is isomorphic to a generalized product of $P(G_1)$ and $P(G_2)$.
We show that the class of groups satisfying the K- and L-theoretic Farrell-Jones conjecture is closed under taking graph products of groups.
We define a free product of connected simple graphs that is equivalent to several existing definitions when the graphs are vertex-transitive but differs otherwise. The new definition is designed for the automorphism group of the free product to be as large as possible, and we give sufficient criteria for it to be non-discrete. Finally, we transfer Tits' classification of automorphisms of trees and simplicity criterion to free products of graphs.
Polyhedral products, graph products and p-central series
本研究建立拓扑空间多面体乘积与群图乘积的联系，将多面体乘积的环路同调代数等同于图乘积中心序列相关李代数的泛包络代数，并应用于直角Coxeter群的下2-中心序列相关限制李代数的描述与对应泛包络代数的等同。
Rotation groups, mediangle graphs, and periagroups: a unified point of view on Coxeter groups and graph products of groups
本文通过旋转群和中角图的统一视角，为Coxeter群和群的图积提供了统一的代数和几何研究框架，并给出了相关结果的统一证明。
Infinite graph product of groups I: Geometry of the extension graph
本文引入图群的扩展图并研究其几何性质，证明扩展图与准中位图的交叉图同构，并应用该图证明图 wreath 产品的相对超几何性，提供新的相对超几何群构造方法。
Given an edge-independent random graph G(n,p), we determine various facts about the cohomology of graph products of groups for the graph G(n,p). In particular, the random graph product of a sequence of finite groups is a rational duality group with probability tending to 1 as n goes to infinity. This includes random right angled Coxeter groups as a special case.
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