Embedding groups into acyclic groups
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Abstract We show that labelled Thompson groups and twisted Brin–Thompson groups are all acyclic. This allows us to prove several new embedding results for groups. First, every group of type Fn embeds quasi-isometrically as a subgroup of an acyclic group of type Fn that has no proper finite-index subgroups. This improves results of Baumslag–Dyer–Heller (n=1) and Baumslag–Dyer–Miller (n=2) from the early 80s, as well as a more recent result of Bridson (n=2). Second, we show that every finitely generated group embeds quasi-isometrically as a subgroup of a 2-generated, simple, acyclic group. Our results also allow us to produce, for each n⩾2, the first known example of an acyclic group that is of type Fn but not Fn+1. These examples can moreover be taken to be simple. Furthermore, our examples provide a rich source of universally boundedly acyclic groups. |