The Borel complexity of von Neumann equivalence

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We prove that for a countable discrete group Γ containing a copy of the free group Fn, for some 2≤n≤∞, as a normal subgroup, the equivalence relations of conjugacy, orbit equivalence and von Neumann equivalence of the ergodic a.e. free probability measure preserving actions of Γ are analytic non-Borel equivalence relations in the Polish space of probability measure preserving Γ-actions. As a consequence we obtain that the isomorphism relations in the spaces of separably acting factors of type II1, II and IIIλ, 0≤λ≤1, are analytic and not Borel when these spaces are given the Effros Borel structure.

Original languageEnglish
Article number102913
JournalAnnals of Pure and Applied Logic
Volume172
Issue number5
Number of pages28
ISSN0168-0072
DOIs
Publication statusPublished - 2021

    Research areas

  • Ergodic theory, Global theory of measure preserving actions, Group measure space factors

ID: 257977197