A survey of Measured Group Theory

Abstract

The title refers to the area of research which studies infinite groups using measure-theoretic tools, and studies the restrictions that group structure imposes on ergodic theory of their actions. The paper is a survey of recent developments focused on the notion of Measure Equivalence between groups, and Orbit Equivalence between group actions. We discuss known invariants and classification results (rigidity) in both areas.

A survey for the Proceedings of a Conference honoring Robert Zimmer's 60th birthday. 61 pages. Referees comments are incorporated, in particular sections 3.1.2 (cost) and 3.1.4 (Cowling Haagerup invariant) were updated. Some new references added