Colloquium abstracts

Sang-hyun Kim
Seoul National University
April 20, 2017

Obstruction for a virtual C^2 action on the circle:  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).