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2509.00829

Generic classification of the quasi-free flows on the Cuntz algebra O2

Robert Neagu

correctmedium confidence
Category
Not specified
Journal tier
Strong Field
Processed
Sep 28, 2025, 12:57 AM

Audit review

The paper proves that for a dense Gδ subset of irrational ratios r = L2/L1 > 0, the quasi-free flow α^L on O2 is classified up to cocycle conjugacy by the unique β solving e^{-βL1}+e^{-βL2}=1, via generic equivariant Z-stability and the Rokhlin property for the dual action, combined with Szabó’s Rokhlin-flow classification and a Takai/Landstad-style reduction back to the original flow (see Theorem 3.12 and its proof, including (3.8) and Proposition 1.2 in the PDF ). The candidate solution reaches the same conclusion but makes a crucial incorrect claim that the crossed product O2 ⋊α R is a Kirchberg algebra; in fact, it is stably projectionless and monotracial in the regime considered, which is central to the paper’s argument (cf. Theorem 3.12 proof ). Hence the model’s proof is flawed even though the final statement matches the paper.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} strong field

\textbf{Justification:}

The manuscript achieves a notable generic classification of quasi-free flows on O2 by exploiting dual Rokhlin actions on a stably projectionless crossed product, together with Szabó’s Rokhlin-flow classification. The methods are clearly articulated, with new technical inputs proving generic Rokhlin property of the dual actions. The result partially answers longstanding questions in the area and is of clear interest to experts in C*-dynamics. Minor clarifications will further strengthen the exposition.