The Borel complexity of von Neumann equivalence
Dynamical Systems
2012-05-22 v3 Group Theory
Logic
Operator Algebras
Abstract
We prove that for a countable discrete group containing a copy of the free group , for some , as a normal subgroup, the equivalence relations of conjugacy, orbit equivalence and von Neumann equivalence of the ergodic a.e. free actions of are analytic non-Borel equivalence relations in the Polish space of probability measure preserving actions. As a consequence we obtain that the isomorphism relation in the spaces of separably acting factors of type , and , , are analytic and not Borel when these spaces are given the Effros Borel structure.
Keywords
Cite
@article{arxiv.1109.2351,
title = {The Borel complexity of von Neumann equivalence},
author = {Inessa Epstein and Asger Tornquist},
journal= {arXiv preprint arXiv:1109.2351},
year = {2012}
}
Comments
28 pages. Minor corrections throughout