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2109.08602

Slow entropy for some Anosov-Katok diffeomorphisms

Shilpak Banerjee, Philipp Kunde, Daren Wei

correctmedium confidence
Category
math.DS
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper explicitly proves that for C∞ AbC diffeomorphisms the upper measure-theoretic slow entropy at the polynomial scale nt vanishes (Section 6.1), via quantitative norm growth of the conjugacies and a covering-number bound imported from BKW, leading to a limit of zero for all t>0 . The model’s argument, while aiming at the same conclusion, hinges on a strong and unsubstantiated assumption that each conjugacy h_i is the identity off a set S_i with summable measures and that commutation failures are localized to S_i. This is not part of the paper’s construction—indeed, the paper uses conjugations that are not supported on summably small sets (e.g., φ_n equals the identity on half a fundamental domain, but the modified region is of fixed positive measure, not summable across stages) . Consequently, key steps in the model proof (uniform exceptional-set estimates and the Markov-inequality step yielding G_n of measure >1−ε independent of n) are not justified for the AbC diffeomorphisms under consideration. The paper’s proof is sound under its stated quantitative hypotheses; the model’s proof is incomplete under assumptions not supplied by the paper.

Referee report (LaTeX)

\textbf{Recommendation:} no revision

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The section proving vanishing of upper measure-theoretic slow entropy at polynomial scale for C∞ AbC diffeomorphisms is concise, technically sound, and fits coherently with the paper’s broader program relating regularity, convergence speed, and slow entropy scales. The result strengthens the narrative by showing a robust obstruction in the C∞ category.