Lamplighters and the bounded cohomology of Thompson's group

Abstract

We prove the vanishing of the bounded cohomology of lamplighter groups for a wide range of coefficients. This implies the same vanishing for a number of groups with self-similarity properties, such as Thompson's group F. In particular, these groups are boundedly acyclic. Our method is ergodic and applies to large transformation groups where the Mather-Matsumoto-Morita method sometimes fails because not all are acyclic in the usual sense.