Séminaires : Séminaire Géométrie et Topologie

Ce séminaire s’adresse aux géomètres, topologues et dynamiciens au sens large. Il est rattaché aux équipes Analyse Algébrique et Analyse Complexe et Géométrie. Les exposés seront accessibles à une audience large, doctorants inclus. Il se tiendra à Jussieu, le jeudi à 11h, en salle 15-25 502. Le séminaire a l'agenda google suivante: https://calendar.google.com/calendar/b/0?cid=dDgzNTJoczNmdDhlMm5nb2IzMXJwaWpsdHNAZ3JvdXAuY2FsZW5kYXIuZ29vZ2xlLmNvbQ

Group actions on CAT(0)-cube complexes play an important role in geometric group theory.  A group G has Property FW if every such action has a fixed point. This property is a combinatorial weakening of Kazhdan’s property (T).
I will give  an introduction to this property through the point of view of commensurating actions, developed by Cornulier. Then, I will explain that there exist groups with Property FW that are amenable (thus very far from being Kazhdan).
These examples arise from the theory of iterated monodromy group, a class of groups of dynamical origin associated to certain expanding maps on compact spaces. They are related to the classical square Sierpińki carpet.
Joint work with Volodia Nekrashevych and Tianyi Zheng.