A proof that all Seifert 3-manifold groups and all virtual surface groups are conjugacy separable

Bianchi groups are conjugacy separable

We prove that non-uniform arithmetic lattices of $SL_2(\mathbb{C})$ and in particular the Bianchi groups are conjugacy separable. The proof based on recent deep results of Agol, Long, Reid and Minasyan.

Virtually compact special hyperbolic groups are conjugacy separable

We prove that any word hyperbolic group which is virtually compact special (in the sense of Haglund and Wise) is conjugacy separable. As a consequence we deduce that all word hyperbolic Coxeter groups and many classical small cancellation groups are conjugacy separable. To get the main result we establish a new criterion for showing that elements of prime order are conjugacy distinguished. This criterion is of independent interest; its proof is based on a combination of discrete and profinite (co)homology theories.

Limit Groups are Subgroup Conjugacy Separable

A group $G$ is called subgroup conjugacy separable if for every pair of non-conjugate finitely generated subgroups of $G$, there exists a finite quotient of $G$ where the images of these subgroups are not conjugate. We prove that limit groups are subgroup conjugacy separable. We also prove this property for one relator groups of the form $R=\langle a_1,...,a_n\mid W^n\rangle$ with $n>|W|$. The property is also proved for virtual retracts (equivalently for quasiconvex subgroups) of hyperbolic virtually special groups.

Separability of double cosets and conjugacy classes in 3-manifold groups

Let M = H^3 / Γbe a hyperbolic 3-manifold of finite volume. We show that if H and K are abelian subgroups of Γand g is in Γ, then the double coset HgK is separable in Γ. As a consequence we prove that if M is a closed, orientable, Haken 3-manifold and the fundamental group of every hyperbolic piece of the torus decomposition of M is conjugacy separable then so is the fundamental group of M. Invoking recent work of Agol and Wise, it follows that if M is a compact, orientable 3-manifold then π_1(M) is conjugacy separable.

On conjugacy separability of fibre products

In this paper we study conjugacy separability of subdirect products of two free (or hyperbolic) groups. We establish necessary and sufficient criteria and apply them to fibre products to produce a finitely presented group $G_1$ in which all finite index subgroups are conjugacy separable, but which has an index $2$ overgroup that is not conjugacy separable. Conversely, we construct a finitely presented group $G_2$ which has a non-conjugacy separable subgroup of index $2$ such that every finite index normal overgroup of $G_2$ is conjugacy separable. The normality of the overgroup is essential in…

Conjugacy in normal subgroups of hyperbolic groups

Let N be a finitely generated normal subgroup of a Gromov hyperbolic group G. We establish criteria for N to have solvable conjugacy problem and be conjugacy separable in terms of the corresponding properties of G/N. We show that the hyperbolic group from F. Haglund's and D. Wise's version of Rips's construction is hereditarily conjugacy separable. We then use this construction to produce first examples of finitely generated and finitely presented conjugacy separable groups that contain non-(conjugacy separable) subgroups of finite index.

$\boldsymbol{\textit{C}}$-遗传共轭可分群与 wreath 积

$\mathcal{C}$-Hereditarily conjugacy separable groups and wreath products

该研究给出限制 wreath 积为 $\boldsymbol{\textit{C}}$-遗传共轭可分群的充要条件，证明 Grigorchuk 群是 2-遗传共轭可分群，构造了无穷多类非多循环遗传共轭可分群。

Virtual pro-$p$ properties of 3-manifold groups

We answer a question of Aschenbrenner and Friedl regarding virtual $p$-efficiency for 3-manifold groups. We then study conjugacy $p$-separability and prove results for Fuchsian groups, Seifert fibre spaces and graph manifolds.

Hereditary conjugacy separability of right angled Artin groups and its applications

We prove that finite index subgroups of right angled Artin groups are conjugacy separable. We then apply this result to establish various properties of other classes of groups. In particular, we show that any word hyperbolic Coxeter group contains a conjugacy separable subgroup of finite index and has a residually finite outer automorphism group. Another consequence of the main result is that Bestvina-Brady groups are conjugacy separable and have solvable conjugacy problem.

Virtual retractions, conjugacy separability and omnipotence

We use wreath products to provide criteria for a group to be conjugacy separable or omnipotent. These criteria are in terms of virtual retractions onto cyclic subgroups. We give two applications: a straightforward topological proof of the theorem of Stebe that infinite-order elements of Fuchsian groups (of the first type) are conjugacy distinguished, and a proof that surface groups are omnipotent.

扭曲共轭与分离性

Twisted conjugacy and separability

研究扭曲共轭分离性及其在群结构中的性质，证明多项式群由nilpotent群由有限群的完全扭曲共轭分离等价于所有商群余有限。

Twisted conjugacy separable groups

We study the notion of twisted conjugacy separability (essentially introduced in our previous paper for a proof of twisted version of Burnside-Frobenius theorem) and some related properties. We give examples of groups with and without this property and study its behavior under some extensions. An affirmative answer to the twisted Dehn conjugacy problem for polycyclic-by-finite group is obtained. Some problems for the further study are indicated.

Groupes fondamentaux des varietes de dimension 3 et algebres d'operateurs

We provide a geometric characterization of manifolds of dimension 3 with fundamental groups of which all conjugacy classes except 1 are infinite, namely of which the von Neumann algebras are factors of type $II_1$: they are essentially the 3-manifolds with infinite fundamental groups on which there does not exist any Seifert fibration. Otherwise said and more precisely, let $M$ be a compact connected 3-manifold and let $Γ$ be its fundamental group, supposed to be infinite and with at least one finite conjugacy class besides 1. If $M$ is orientable, then $Γ$ is the fundamental group of a Seifer…

自由-循环群是共轭可分离的

Free-by-cyclic groups are conjugacy separable

本文证明了所有有限生成的自由-循环群都是共轭可分离的，并展示了外自同构群的残余有限性。

Conjugacy p-separability of right-angled Artin groups and applications

We prove that every subnormal subgroup of p-power index in a right-angled Artin group is conjugacy p-separable. As an application, we prove that every right-angled Artin group is conjugacy separable in the class of torsion-free nilpotent groups. As another application, we prove that the outer automorphism group of a right-angled Artin group is virtually residually p-finite. We also prove that the Torelli group of a right-angled group is residually torsion-free nilpotent, hence residually p-finite and bi-orderable.

Magnus pairs in, and free conjugacy separability of, limit groups

There are limit groups having non-conjugate elements whose images are conjugate in every free quotient. Towers over free groups are freely conjugacy separable.

Decision problems, complexity, traces, and representations

In this article, we study connections between representation theory and efficient solutions to the conjugacy problem on finitely generated groups. The main focus is on the conjugacy problem in conjugacy separable groups, where we measure efficiency in terms of the size of the quotients required to distinguish a distinct pair of conjugacy classes.

On the Conjugacy Separability of Generalized Free Products of Groups

It is proved that generalized free product of two finite p-groups is a conjugacy p-separable group if and only if it is residually finite p-groups. This result is then applied to establish some sufficient conditions for conjugacy p-separability of generalized free product of infinite groups.

Residual $p$ properties of mapping class groups and surface groups

Let $\mathcal M (Σ, \mathcal P)$ be the mapping class group of a punctured oriented surface $(Σ, \mathcal P)$ (where $\mathcal P$ may be empty), and let $\mathcal T_p(Σ,\mathcal P)$ be the kernel of the action of $\mathcal M (Σ, \mathcal P)$ on $H_1 (Σ\setminus \mathcal P, \mathbb F_p)$. We prove that $\mathcal T_p(Σ, \mathcal P)$ is residually $p$. In particular, this shows that $\mathcal M (Σ, \mathcal P)$ is virtually residually $p$. For a group $G$ we denote by $\mathcal I_p(G)$ the kernel of the natural action of ${\rm Out} (G)$ on $H_1(G, \mathbb F_p)$. In order to achieve our theorem, w…

Quantifying conjugacy separability in wreath products of groups

We study generalisations of conjugacy separability in restricted wreath products of groups. We provide an effective upper bound for $\mathcal{C}$-conjugacy separability of a wreath product $A \wr B$ in terms of the $\mathcal{C}$-conjugacy separability of $A$ and $B$, the growth of $\mathcal{C}$-cyclic subgroup separability of $B$, and the $\mathcal{C}$-residual girth of $B.$ As an application, we provide a characterisation of when $A \wr B$ is $p$-conjugacy separable. We use this characterisation to the provide for each prime $p$ an example of wreath products with infinite base group that are …

关于普通与广义Baumslag-Solitar群的共轭可分性

On the conjugacy separability of ordinary and generalized Baumslag-Solitar groups

该研究聚焦普通与广义Baumslag-Solitar（GBS）群的共轭可分性问题，在特定周期群类的封闭性条件下，推导非可解与可解GBS群的共轭可分判别准则，并得出GBS群共轭有限可分等价于剩余有限的推论。

Subgroup conjugacy separability for surface groups

A group $G$ is called subgroup conjugacy separable (abbreviated as SCS), if any two finitely generated and non-conjugate subgroups of $G$ remain non-conjugate in some finite quotient of $G$. We prove that free groups and the fundamental groups of orientable closed compact surfaces are SCS.

On the conjugacy separability in the class of finite $p$-groups of finitely generated nilpotent groups

It is proved that for any prime $p$ a finitely generated nilpotent group is conjugacy separable in the class of finite $p$-groups if and only if the torsion subgroup of it is a finite $p$-group and the quotient group by the torsion subgroup is abelian.

几乎阿贝尔群的有效共轭可分性

Effective conjugacy separability of virtually abelian groups

本文刻画了每个几乎阿贝尔群的共轭可分性函数，发现当扩张对应不可约表示时与剩余有限性函数相同，否则可能严格更大，并给出示例。

剩余自由群中的子群共轭可分性

Subgroup Conjugacy Separability in Residually Free Groups

本文研究剩余自由群的子群共轭性质，证明有限展示情形具有子群共轭可分性，$FP_\infty$ 型还具可辨识性，并推出其外自同构群剩余有限。

Injectors in $π$-separable groups

Let $π$ be a set of primes. We show that $π$-separable groups have a conjugacy class of $\mathfrak F$-injectors for suitable Fitting classes $\mathfrak F$, which coincide with the usual ones when specializing to soluble groups.

On subgroup conjugacy separability in the class of virtually free groups

A group G is called subgroup conjugacy separable (abbreviated as SCS), if any two finitely generated and non-conjugate subgroups of G remain non-conjugate in some finite quotient of G. We prove that the free groups and the fundamental groups of finite trees of finite groups with some normalizer condition are SCS. We also introduce the subgroup into-conjugacy separability property and prove that the above groups have this property too.

Extension of Carter subgroups in $π$-separable groups

Let $π$ be a set of primes. We show that $π$-separable groups have a conjugacy class of subgroups which specialize to Carter subgroups, i.e. self-normalizing nilpotent subgroups, or equivalently, nilpotent projectors, when specializing to soluble groups.

幂零群中共轭可分性增长的统一上界

Uniform Upper Bounds for Conjugacy Separability Growth in Nilpotent Groups

针对幂零群的共轭可分性增长函数，本文给出次数至多线性于幂零类、二次于Hirsch长度的显式多项式上界，并证明二步幂零情形下该界最优，同时纠正了文献错误。

关于子代数的共轭与扰动

On conjugacy and perturbation of subalgebras

本文研究迹冯·诺依曼代数中子代数的共轭轨道，构造了使具有Haagerup性质或性质(T)的子代数分别具有唯一嵌入的II$_1$因子，并讨论了可分性与密度特征。

论群的某些扩张的广义（扭曲）共轭可分性

On generalized (twisted) conjugacy separability of some extensions of groups

引入广义共轭可分性性质，证明群$G$在有限与循环扩张下扭曲共轭、Brinkmann共轭等可分性的等价与蕴含关系，并应用于自由群等群类。

On conjugacy separability of some Coxeter groups and parabolic-preserving automorphisms

We prove that even Coxeter groups, whose Coxeter diagrams contain no (4,4,2) triangles, are conjugacy separable. In particular, this applies to all right-angled Coxeter groups or word hyperbolic even Coxeter groups. For an arbitrary Coxeter group W, we also study the relationship between Coxeter generating sets that give rise to the same collection of parabolic subgroups. As an application we show that if an automorphism of W preserves the conjugacy class of every sufficiently short element then it is inner. We then derive consequences for the outer automorphism groups of Coxeter groups.

任意剩余有限性与共轭可分性增长

Arbitrary residual finiteness and conjugacy separability growth

本文证明了Bradford构造的群具有共轭可分性且其增长等于剩余有限性增长，并扩展构造出新群，证明这两种增长函数能独立变化且可任意远离。

On subgroup conjugacy separability of hyperbolic QVH-groups

A group $G$ is called subgroup conjugacy separable (abbreviated as SCS) if any two finitely generated and non-conjugate subgroups of $G$ remain non-conjugate in some finite quotient of $G$. An into-conjugacy version of SCS is abbreviated by SICS. We prove that if $G$ is a hyperbolic group, $H_1$ is a quasiconvex subgroup of $G$, and $H_2$ is a subgroup of $G$ which is elementwise conjugate into $H_1$, then there exists a finite index subgroup of $H_2$ which is conjugate into $H_1$. As corollary, we deduce that fundamental groups of closed hyperbolic 3-manifolds and torsion-free small cancellat…

具有互质大小共轭类的群

Groups with conjugacy classes of coprime sizes

针对有限群中位于互质大小共轭类的元素，证明其共轭类生成子群的交为阿贝尔正规子群，并推广$π$-正则元共轭类乘积的性质，扩展了$p$-正则共轭类公因子图的相关结果。

On the residual finiteness of outer automorphisms of relatively hyperbolic groups

We show that every virtually torsion-free subgroup of the outer automorphism group of a conjugacy separable relatively hyperbolic group is residually finite. As a direct consequence, we obtain that the outer automorphism group of a limit group is residually finite.

Complete Reducibility and Separability

Let G be a reductive linear algebraic group over an algebraically closed field of characteristic p > 0. A subgroup of G is said to be separable in G if its global and infinitesimal centralizers have the same dimension. We study the interaction between the notion of separability and Serre's concept of G-complete reducibility for subgroups of G. The separability hypothesis appears in many general theorems concerning G-complete reducibility. We demonstrate that many of these results fail without this hypothesis. On the other hand, we prove that if G is a connected reductive group and p is very go…

On the residual finiteness of outer automorphisms of relatively hyperbolic groups

We show that every virtually torsion-free subgroup of the outer automorphism group of a conjugacy separable hyperbolic group is residually finite. As a result, we are able to prove that the group of outer automorphisms of every finitely generated Fuchsian group and of every free-by-finite group is resudually finite. We also generalize the main result for relatively hyperbolic groups.

p-正则类上具有无三角图的群

Groups with triangle-free graphs on p-regular classes

该研究针对素数p，对满足“任三个非中心p-正则元共轭类中必有两类长度互素”的有限p-可分群的p-结构展开分类，推进了群论中相关结构问题的研究。

某些Halls群的余有限性质

Residual finiteness properties of some of Halls groups

本文研究了某些Halls群的余有限性质，构造了具有不同共轭分离增长和余有限性增长的群类，并首次展示了余有限性增长介于多项式与指数之间的例子。

On finitely generated normal subgroups of right-angled Artin groups and graph products of groups

A classical result of Schreier states that nontrivial finitely generated normal subgroups of free groups are of finite index, that is, free groups can only quotient to finite groups with finitely generated kernel. In this note we extend this result to the class of right-angled Artin groups (RAAGs). More precisely, we prove that the quotient of a RAAG by a finitely generated (full) normal subgroup is abelian-by-finite and finite-by-abelian. As Schreier's result extends to nontrivial free products of groups, we further show that our result extends to graph products of groups. As a corollary, we …

p-正则类上的公因子图直径为3的群

Groups whose common divisor graph on $p$-regular classes has diameter three

本文针对有限p-可分群的p-正则元素非中心共轭类公因子图Γ_p(G)，正面解答了最大基数顶点与其他顶点最大距离的公开问题，并研究了该图直径为3时群的p-结构。

Profinite properties of graph manifolds

Let $M$ be a closed, orientable, irreducible, geometrizable 3-manifold. We prove that the profinite topology on the fundamental group of $π_1(M)$ is efficient with respect to the JSJ decomposition of $M$. We go on to prove that $π_1(M)$ is good, in the sense of Serre, if all the pieces of the JSJ decomposition are. We also prove that if $M$ is a graph manifold then $π_1(M)$ is conjugacy separable.

Finite Affine Groups: Cycle Indices, Hall-Littlewood Polynomials, and Probabilistic Algorithms

The asymptotic study of the conjugacy classes of a random element of the finite affine group leads one to define a probability measure on the set of all partitions of all positive integers. Four different probabilistic understandings of this measure are given--three using symmetric function theory and one using Markov chains. This leads to non-trivial enumerative results. Cycle index generating functions are derived and are used to compute the large dimension limiting probabilities that an element of the affine group is separable, cyclic, or semisimple and to study the convergence to these lim…

有限典型群的不变生成

Invariable generation of finite classical groups

本文将对称群中三、四个随机元素不变生成概率的结论推广至有限典型群，利用可分元素与极大环面-Weyl群共轭类对应，证明四元概率一致有界远离零、三元概率随q和r趋无穷而趋于零。

On endomorphisms of torsion-free hyperbolic groups

Let $H$ be a torsion-free $δ$-hyperbolic group with respect to a finite generating set $S$. Let $a_1,..., a_n$ and $a_{1*},..., a_{n*}$ be elements of $H$ such that $a_{i*}$ is conjugate to $a_i$ for each $i=1,..., n$. Then, there is a uniform conjugator if and only if $W(a_{1*},..., a_{n*})$ is conjugate to $W(a_1,..., a_n)$ for every word $W$ in $n$ variables and length up to a computable constant depending only on $δ$, $\sharp{S}$ and $\sum_{i=1}^n |a_i|$. As a corollary, we deduce that there exists a computable constant $\mathcal{C}=\mathcal{C}(δ, \sharp S)$ such that, for any endomorphism…

On equationally Noetherian and residually finite groups

The aim of this paper is to compare and contrast the class of residually finite groups with the class of equationally Noetherian groups - groups over which every system of coefficient-free equations is equivalent to a finite subsystem. It is easy to construct groups that are residually finite but not equationally Noetherian (e.g. the direct sum of all finite groups) or vice versa (e.g. the additive group $(\mathbb{Q},+)$ of the rationals). However, no explicit examples that are finitely generated seem to appear in the literature. In this paper, we show that among finitely generated groups, the…

Cocycle and Orbit Equivalence Superrigidity for Malleable Actions of w-Rigid Groups

We prove that if a countable discrete group $Γ$ is {\it w-rigid}, i.e. it contains an infinite normal subgroup $H$ with the relative property (T) (e.g. $Γ= SL(2,\Bbb Z) \ltimes \Bbb Z^2$, or $Γ= H \times H'$ with $H$ an infinite Kazhdan group and $H'$ arbitrary), and $\Cal V$ is a closed subgroup of the group of unitaries of a finite von Neumann algebra (e.g. $\Cal V$ countable discrete, or separable compact), then any $\Cal V$-valued measurable cocycle for a measure preserving action $Γ\curvearrowright X$ of $Γ$ on a probability space $(X,μ)$ which is weak mixing on $H$ and {\it s-malleable} …

The profinite completion of the fundamental group of infinite graphs of groups

Let $(\mathcal{G},Γ)$ be an abstract graph of finite groups. If $Γ$ is finite, we can construct a profinite graph of groups in a natural way $(\hat{\mathcal{G}},Γ)$, where $\hat{\mathcal{G}}(m)$ is the profinite completion of $\mathcal{G}(m)$ for all $m \in Γ$. The main reason for this is that $Γ$ is finite, so it is already profinite. In this paper we deal with the infinite case, by constructing a profinite graph $\overlineΓ$ where $Γ$ is densely embedded and then defining a profinite graph of groups $(\widehat{\mathcal{G}},\overlineΓ)$. We also prove that the fundamental group $Π_1(\widehat{…

通过覆盖的同调群刻画 Riemann 曲面上的闭曲线

Characterizing closed curves on Riemann surfaces via homology groups of coverings

本文利用无分歧 $p$-覆盖紧化同调群中的辛子模检测闭曲线几何交，并通过 $p$-进 Reidemeister 配对刻画正交性，进而几何证明有向曲面群的共轭 $p$-可分性。

一个稳健的剩余有限群族；剩余有限增长谱、可计算性性质及其他应用（附 Arman Darbinyan 和 Emmanuel Rauzy 的附录）

A robust family of residually finite groups; spectra of residual finiteness growth, computability properties, and other applications (with an appendix by Arman Darbinyan and Emmanuel Rauzy)

本文引入一个剩余有限群族，证明满足特定快速增长条件的函数均可实现为二元生成可解群的剩余有限增长函数，并刻画其与字问题可判定性、左可计算函数及递归可枚举图灵度的关系，进而回答了若干公开问题。