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We characterize the solvable Lie groups of the form ${\mathbb R}^m\rtimes {\mathbb R}$, whose $C^*$-algebras are quasidiagonal. Using this result, we determine the connected simply connected solvable Lie groups of type~I whose…

Operator Algebras · Mathematics 2018-02-12 Ingrid Beltita , Daniel Beltita

We define strict C(n) small-cancellation complexes, intermediate to C(n) and C(n+1), and we prove groups acting properly cocompactly on a simply-connected strict C(6) complex are hyperbolic relative to a collection of maximal virtually free…

Group Theory · Mathematics 2025-05-28 Zachary Munro , Daniel T. Wise

We consider two families of subgroups of a group. Each subgroup which belongs to one family is contained in some subgroup which belongs to the other family. We then discuss relations of relative hyperbolicity for the group with respect to…

Group Theory · Mathematics 2013-01-18 Yoshifumi Matsuda , Shin-ichi Oguni , Saeko Yamagata

A closed subgroup of a semisimple algebraic group is called irreducible if it lies in no proper parabolic subgroup. In this paper we classify all irreducible subgroups of exceptional algebraic groups $G$ which are connected, closed and…

Group Theory · Mathematics 2022-09-22 Adam Thomas

We examine the question of quasidiagonality for C*-algebras of discrete amenable groups from a variety of angles. We give a quantitative version of Rosenberg's theorem via paradoxical decompositions and a characterization of…

Operator Algebras · Mathematics 2013-06-19 José Carrión , Marius Dadarlat , Caleb Eckhardt

We prove that the Heisenberg groups can be distinguished from the other connected and simply connected Lie groups via their group $C^*$-algebras. The main step of the proof is a characterization of the nilpotent Lie groups among the…

Operator Algebras · Mathematics 2024-10-01 Ingrid Beltita , Daniel Beltita

We prove a uniqueness theorem and give a characterization of simplicity for Steinberg algebras associated to non-Hausdorff ample groupoids. We also prove a uniqueness theorem and give a characterization of simplicity for the C*-algebra…

Operator Algebras · Mathematics 2019-05-17 Lisa Orloff Clark , Ruy Exel , Enrique Pardo , Aidan Sims , Charles Starling

We characterize relatively norm compact sets in the regular $C^*$-algebra of finitely generated Coxeter groups using a geometrically defined positive semigroup acting on the algebra.

Operator Algebras · Mathematics 2012-07-09 Gero Fendler

We suggest a new approach to the study of relatively hyperbolic groups based on relative isoperimetric inequalities. Various geometric, algebraic, and algorithmic properties are discussed.

Group Theory · Mathematics 2015-01-29 D. V. Osin

This arXived paper has two independant parts, that are improved and corrected versions of different parts of a single paper once named "On equations in relatively hyperbolic groups". The first part is entitled "Existential questions in…

Group Theory · Mathematics 2020-07-20 Francois Dahmani

An algebra is said to be quasi-directly finite when any left-invertible element in its unitization is automatically right-invertible. It is an old observation of Kaplansky that the von Neumann algebra of a discrete group has this property;…

Operator Algebras · Mathematics 2010-06-08 Yemon Choi

In this paper it is proved that relative hyperbolicity is an invariant of quasi-isometry. As a byproduct of the arguments, simplified definitions of relative hyperbolicity are obtained. In particular we obtain a new definition very similar…

Group Theory · Mathematics 2007-05-23 Cornelia Drutu

In this paper we consider convex co-compact subgroups of the projective linear group. We prove that such a group is relatively hyperbolic with respect to a collection of virtually Abelian subgroups of rank two if and only if each open face…

Geometric Topology · Mathematics 2024-07-31 Mitul Islam , Andrew Zimmer

We construct the first known infinite family of quasi-isometry classes of subgroups of hyperbolic groups which are not hyperbolic and are of type $\mathrm{FP}(\mathbb{Q})$. We give a simple criterion for producing many non-hyperbolic…

Group Theory · Mathematics 2024-04-18 Monika Kudlinska

The purpose of this note is to provide a short alternate proof that (combined with a theorem proven by Szczepanski) shows that a group which is relatively hyperbolic in the sense of the definition of Gromov is relatively hyperbolic in the…

Group Theory · Mathematics 2007-05-23 Inna Bumagin

We give new characterizations to ensure that a free product of groups with amalgamation has a simple reduced group C*-algebra, and provide a concrete example of an amalgam with trivial kernel, such that its reduced group C*-algebra has a…

Operator Algebras · Mathematics 2017-12-01 Nikolay A. Ivanov , Tron Omland

We show that properly and cocompactly cubulated relatively hyperbolic groups are virtually special, provided the peripheral subgroups are virtually special in a way that is compatible with the cubulation. This extends Agol's result for…

Group Theory · Mathematics 2023-05-24 Eduardo Oregón-Reyes

For relatively hyperbolic groups, we investigate conditions guaranteeing that the subgroup generated by two relatively quasiconvex subgroups $Q_1$ and $Q_2$ is relatively quasiconvex and isomorphic to $Q_1 \ast_{Q_1 \cap Q_2} Q_2$. The main…

Geometric Topology · Mathematics 2014-10-01 Eduardo Martinez-Pedroza , Alessandro Sisto

Let $n$ be a natural number. Recall that a C*-algebra is said to be $n$-subhomogeneous if all its irreducible representations have dimension at most $n$. In this short note, we give various approximation properties characterising…

Operator Algebras · Mathematics 2019-09-11 Tatiana Shulman , Otgonbayar Uuye

We construct several series of explicit presentations of infinite hyperbolic groups enjoying Kazhdan's property (T). Some of them are significantly shorter than the previously known shortest examples. Moreover, we show that some of those…

Group Theory · Mathematics 2021-01-05 Pierre-Emmanuel Caprace , Marston Conder , Marek Kaluba , Stefan Witzel