Characteristic-invariant conjecture for almost periodic actions on the hyperfinite type II_1 factor
Characteristic-invariant conjecture for almost periodic actions on the hyperfinite type II_1 factor
Let be the acting group and let be the hyperfinite type factor. Let be an almost periodic action such that is a factor. Define
and, for , choose with . The associated bicharacter is , defined by .
Characteristic-invariant conjecture. The action is classified up to cocycle conjugacy by the characteristic invariant .
The source identifies this as the remaining case in the classification of almost periodic actions on the hyperfinite type factor when the crossed product is a factor but the action is not outer. The status of this classification problem is not resolved in the supplied text.
Progress summary
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Sources & referencesView supporting material
Primary source
Cyril Houdayer and Amine Marrakchi, “Uniqueness of almost periodic outer flows on the hyperfinite type II_1 factor”, arXiv:2605.02781 (2026).
Additional references
2 papers in this index state this conjecture (2018–2026). The statement above is taken from the most recent of them; the others are arXiv:1803.06870.
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