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arXiv · 1710.10771

Non-classification of Cartan subalgebras for a class of von Neumann algebras

Pieter Spaas
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Abstract

We study the complexity of the classification problem for Cartan subalgebras in von Neumann algebras. We construct a large family of II$_1$ factors whose Cartan subalgebras up to unitary conjugacy are not classifiable by countable structures, providing the first such examples. Additionally, we construct examples of II$_1$ factors whose Cartan subalgebras up to conjugacy by an automorphism are not classifiable by countable structures. Finally, we show directly that the Cartan subalgebras of the hyperfinite II$_1$ factor up to unitary conjugacy are not classifiable by countable structures, and deduce that the same holds for any McDuff II$_1$ factor with at least one Cartan subalgebra.

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Pieter Spaas. 2017-10-30. Non-classification of Cartan subalgebras for a class of von Neumann algebras. https://arxiv.org/abs/1710.10771

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