On Popa's Cocycle Superrigidity Theorem
arXiv:math/0608364
Abstract
These notes contain an Ergodic-theoretic account of the Cocycle Superrigidity Theorem recently discovered by Sorin Popa. We state and prove a relative version of the result, discuss some applications to measurable equivalence relations, and point out that Gaussian actions (of ``rigid'' groups) satisfy the assumptions of Popa's theorem.
v.2: slight changes in the presentation, (some) typos corrected, wq-normal subgroups added. 35 pages