Extensive amenability of group actions

Vortrag von Dr. Nicolas Matte Bon

Datum: 29.03.17  Zeit: 17.15 - 19.00  Raum: Y27H12

A group is amenable if the spectral radius of any symmetric random walk on it is equal to one. This is only one among the many equivalent characterisations of this property, that make it play a role in many aspects of group theory. Nevertheless, deciding wether a group is amenable or not can be a difficult problem. Extensive amenability is a property of group actions, first considered by Juschenko and Monod, that leads to a method to prove amenability of groups. I will explain this property and give a a probabilistic reformulation of it, then explain this method and illustrate it by proving amenability of some groups of interval exchange transformations. Finally I will highlight the current limits of this method and some related open questions.
Talk based on a joint work with Juschenko, Monod, and de la Salle.