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Residual properties of graph products of groups  [PDF]
Federico Berlai,Michal Ferov
Mathematics , 2015,
Abstract: 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.
Intersection graph of cyclic subgroups of groups  [PDF]
R. Rajkumar,P. Devi
Mathematics , 2015,
Abstract: Let $G$ be a group. The intersection graph of cyclic subgroups of $G$, denoted by $\mathscr I_c(G)$, is a graph having all the proper cyclic subgroups of $G$ as its vertices and two distinct vertices in $\mathscr I_c(G)$ are adjacent if and only if their intersection is non-trivial. In this paper, we classify the finite groups whose intersection graph of cyclic subgroups is one of totally disconnected, complete, star, path, cycle. We show that for a given finite group $G$, $girth(\mathscr I_c (G)) \in \{3, \infty\}$. Moreover, we classify all finite non-cyclic abelian groups whose intersection graph of cyclic subgroups is planar. Also for any group $G$, we determine the independence number, clique cover number of $\mathscr I_c (G)$ and show that $\mathscr I_c (G)$ is weakly $\alpha$-perfect. Among the other results, we determine the values of $n$ for which $\mathscr I_c (\mathbb{Z}_n)$ is regular and estimate its domination number.
Sofic groups: graph products and graphs of groups  [PDF]
Laura Ciobanu,Derek F. Holt,Sarah Rees
Mathematics , 2012,
Abstract: 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.
Knapsack in graph groups, HNN-extensions and amalgamated products  [PDF]
Markus Lohrey,Georg Zetzsche
Computer Science , 2015,
Abstract: It is shown that the knapsack problem, which was introduced by Myasnikov et al. for arbitrary finitely generated groups, can be solved in NP for graph groups. This result even holds if the group elements are represented in a compressed form by SLPs, which generalizes the classical NP-completeness result of the integer knapsack problem. We also prove general transfer results: NP-membership of the knapsack problem is passed on to finite extensions, HNN-extensions over finite associated subgroups, and amalgamated products with finite identified subgroups.
Surface subgroups of right-angled Artin groups  [PDF]
John Crisp,Michah Sageev,Mark Sapir
Mathematics , 2007,
Abstract: We consider the question of which right-angled Artin groups contain closed hyperbolic surface subgroups. It is known that a right-angled Artin group $A(K)$ has such a subgroup if its defining graph $K$ contains an $n$-hole (i.e. an induced cycle of length $n$) with $n\geq 5$. We construct another eight "forbidden" graphs and show that every graph $K$ on $\le 8$ vertices either contains one of our examples, or contains a hole of length $\ge 5$, or has the property that $A(K)$ does not contain hyperbolic closed surface subgroups. We also provide several sufficient conditions for a \RAAG to contain no hyperbolic surface subgroups. We prove that for one of these "forbidden" subgraphs $P_2(6)$, the right angled Artin group $A(P_2(6))$ is a subgroup of a (right angled Artin) diagram group. Thus we show that a diagram group can contain a non-free hyperbolic subgroup answering a question of Guba and Sapir. We also show that fundamental groups of non-orientable surfaces can be subgroups of diagram groups. Thus the first integral homology of a subgroup of a diagram group can have torsion (all homology groups of all diagram groups are free Abelian by a result of Guba and Sapir).
Products of finite groups and nonmeasurable subgroups  [PDF]
F. Javier Trigos-Arrieta
Mathematics , 2014,
Abstract: It is proven that if $G$ is a finite group, then $G^\omega$ has $2^{\mathfrak c}$ dense nonmeasurable subgroups. Also, other examples of compact groups with dense nonmeasurable subgroups are presented.
Rigidity of graph products of groups  [PDF]
David G. Radcliffe
Mathematics , 2002, DOI: 10.2140/agt.2003.3.1079
Abstract: We show that if a group can be represented as a graph product of finite directly indecomposable groups, then this representation is unique.
Commensurator Subgroups of Surface Groups
OCAMPO URIBE,OSCAR EDUARDO;
Revista Colombiana de Matemáticas , 2010,
Abstract: let m be a surface, and let h be a subgroup of π1m. in this paper we study the commensurator subgroup c\\pi_1m(h) of π1m, and we extend a result of l. paris and d. rolfsen [7], when h is a geometric subgroup of π1m. we also give an application of commensurator subgroups to group representation theory. finally, by considering certain closed curves on the klein bottle, we apply a classification of these curves to self-intersection nielsen theory.
On Products of Quasiconvex Subgroups in Hyperbolic Groups  [PDF]
Ashot Minasyan
Mathematics , 2004,
Abstract: An interesting question about quasiconvexity in a hyperbolic group concerns finding classes of quasiconvex subsets that are closed under finite intersections. A known example is the class of all quasiconvex subgroups. However, not much is yet learned about the structure of arbitrary quasiconvex subsets. In this work we study the properties of products of quasiconvex subgroups; we show that such sets are quasiconvex, their finite intersections have a similar algebraic representation and, thus, are quasiconvex too.
Random graphs of free groups contain surface subgroups  [PDF]
Danny Calegari,Henry Wilton
Mathematics , 2013,
Abstract: A random graph of free groups contains a surface subgroup
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