English

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 Γ\Gamma containing a copy of the free group \Fn\F_n, for some 2n2\leq n\leq\infty, as a normal subgroup, the equivalence relations of conjugacy, orbit equivalence and von Neumann equivalence of the ergodic a.e. free actions of Γ\Gamma are analytic non-Borel equivalence relations in the Polish space of probability measure preserving Γ\Gamma actions. As a consequence we obtain that the isomorphism relation in the spaces of separably acting factors of type \II1\II_1, \II\II_\infty and \IIIλ\III_\lambda, 0λ10\leq\lambda\leq 1, 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