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Article Dans Une Revue Groups, Geometry, and Dynamics Année : 2021

CAT(0) cube complexes and inner amenability

Résumé

We here consider inner amenability from a geometric and group theoretical perspective. We prove that for every non-elementary action of a group G on a finite dimensional irreducible CAT(0) cube complex, there is a nonempty G-invariant closed convex subset such that every conjugation invariant mean on G gives full measure to the stabilizer of each point of this subset. Specializing our result to trees leads to a complete characterization of inner amenability for HNN-extensions and amalgamated free products. One novelty of the proof is that it makes use of the existence of certain idempotent conjugation-invariant means on G. We additionally obtain a complete characterization of inner amenabil-ity for permutational wreath product groups. One of the main ingredients used for this is a general lemma which we call the location lemma, which allows us to "locate" conjugation invariant means on a group G relative to a given normal subgroup N of G. We give several further applications of the location lemma beyond the aforementioned characterization of inner amenable wreath products.
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Dates et versions

hal-02066656 , version 1 (13-03-2019)

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Bruno Duchesne, Robin Tucker-Drob, Phillip Wesolek. CAT(0) cube complexes and inner amenability. Groups, Geometry, and Dynamics, 2021, ⟨10.4171/GGD/601⟩. ⟨hal-02066656⟩
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