Invariant random subgroups, elementwise conservative actions and boomerang subgroupsGeometric Group Theory Oberseminar

by Prof. Waltraud Lederle (Uni Bielefeld)

Wednesday Nov 19, 2025, 11:00 AM → 12:00 PM Europe/Berlin

Endenicher Allee 60/0-008 (Mathezentrum)

 Invariant random subgroups, which are probability measures on sets of subgroups, have been an important subject of research in the last 15 years and can be thought of as point stabilizers of probability measure preserving (p.m.p.) actions. We are introducing elementwise conservative (EC) actions as generalizations of p.m.p. actions, and boomerang subgroups as "generic instances" of EC actions. I will talk about what these objects are, what they have in common and what tells them apart. Topics that we will adress in this talks are Margulis' normal subgroup theorem and the Stuck-Zimmer rigidity thorem, Poincaré recurrence, non-singular dynamics, Schreier graphs and critical exponents or growth rates.