Speaker: Sang-hyun Kim
Date: April 20, 2017
Affiliation: Seoul National University

Abstract: When does a group virtually admit a faithful $C^2$ action on the circle? We provide an obstruction using a certain group defined by commutators. Examples include all (non-virtually-free) mapping class groups, Out(Fn) and Torelli groups. This answers a question of Farb. (Joint work with Hyungryul Baik and Thomas Koberda).