English

Some computations of 1-cohomology groups and construction of non orbit equivalent actions

Operator Algebras 2007-05-23 v6 Group Theory

Abstract

For each group GG having an infinite normal subgroup with the relative property (T) (for instance G=H×KG = H \times K where HH is infinite with property (T) and KK is arbitrary), and any countable abelian group Λ\Lambda we construct free ergodic measure preserving actions σΛ\sigma_\Lambda of GG on the probability space such that the 1'st cohomology group of σΛ\sigma_\Lambda, H1(σΛ)H^1(\sigma_\Lambda), is equal to Char(G)×Λ(G) \times \Lambda. We deduce that GG has uncountably many non stably orbit equivalent actions. We also calculate 1-cohomology groups and show existence of ``many'' non stably orbit equivalent actions for free products of groups as above.

Keywords

Cite

@article{arxiv.math/0407199,
  title  = {Some computations of 1-cohomology groups and construction of non orbit equivalent actions},
  author = {Sorin Popa},
  journal= {arXiv preprint arXiv:math/0407199},
  year   = {2007}
}

Comments

24 pages (final version, with slight additions and change of title on 09/20/04)