Non-embeddable II$_1$ factors resembling the hyperfinite II$_1$ factor

TL;DR

This paper explores properties that characterize the hyperfinite II$_1$ factor among non-embeddable II$_1$ factors, using model-theoretic techniques to establish equivalences and provide new proofs of known properties.

Contribution

It introduces new characterizations of the hyperfinite II$_1$ factor in the non-embeddable setting and applies model theory to analyze these properties.

Findings

A II$_1$ factor has the Jung property iff it is self-tracially stable.

The enforceable factor, if it exists, has these properties.

Model-theoretic techniques provide new proofs of hyperfinite II$_1$ factor properties.

Abstract

We consider various statements that characterize the hyperfinite II$_1$ factors amongst embeddable II$_1$ factors in the non-embeddable situation. In particular, we show that "generically" a II$_1$ factor has the Jung property (which states that every embedding of itself into its ultrapower is unitarily conjugate to the diagonal embedding) if and only if it is self-tracially stable (which says that every such embedding has an approximate lifting). We prove that the enforceable factor, should it exist, has these equivalent properties. Our techniques are model-theoretic in nature. We also show how these techniques can be used to give new proofs that the hyperfinite II$_1$ factor has the aforementioned properties.