Dice Question Streamline Icon: https://streamlinehq.com

Uniform spectral gap property (P1) for non-full factors

Ascertain whether the following uniform spectral gap property holds for non-full factors M: for every automorphism θ ∈ Aut(M) that is not approximately inner (θ ∉ \overline{Inn}(M)), there exists a neighborhood U of the class \underline{p}(θ) in \underline{Out}(M) = Aut(M)/\overline{Inn}(M) such that the standard M–M bimodule 2(id) is not weakly contained in the direct sum \bigoplus_{β ∈ \underline{p}^{-1}(U)} 2(β), where 2(β) denotes the M–M bimodule associated to β.

Information Square Streamline Icon: https://streamlinehq.com

Background

Jones proved a uniform spectral gap property (P2) for full II1 factors, and Marrakchi–Vaes extended such uniformity to full σ-finite factors. The weaker property (P1) would suffice, together with topological outerness of an action, to deduce strict outerness via a general mechanism outlined by the authors.

However, the existence of a uniform spectral gap at the automorphism-group level for non-full factors remains unresolved. The authors explicitly state that even the weaker property (P1) is unknown in this generality, underscoring a key open direction in the extension of rigidity phenomena beyond the full factor case.

References

We don't even know if the weaker property \hyperref[P1]{P1} holds for non-full factors.

Strictly outer actions of locally compact groups: beyond the full factor case (2407.11738 - Morando, 16 Jul 2024) in Preliminaries, paragraph “Spectral gaps,” after the discussion of properties P1 and P2