Ομιλητής: Αλέξανδρος Κεχρής, Caltech

Τίτλος:Weak containment and invariant random subgroups

Περίληψη: In this talk I will first give an introduction to the concept of weak containment for measure preserving actions of countable groups,which gives a hierarchical order of complexity for such actions. The associated weak equivalence relation of actions can be viewed as a coarse version of isomorphism between such actions which behaves much more smoothly than isomorphism itself. In particular the space of weak equivalence classes admits a natural compact, metrizable topology. 
I will consider questions concerning the continuity of certain basic operations in this quotient space and their connection with properties of groups such as amenability or freeness. Finally I will discuss how these problems are related with the concept of invariant random subgroup, which is a random version of normality.