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2201.09326

An Improved Convergence Case for Diophantine Approximations on IFS Fractals

Itamar Cohen-Matalon

correcthigh confidence
Category
Not specified
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper proves the convergence part of a Khinchine-type theorem on self-similar IFS fractals for all exponents 0 < α < ϖ, where ϖ = min_l α_l(μ_K)(d−l+1), by importing a contraction hypothesis from Khalil and using random-walk/homogeneous-dynamics tools plus the Dani correspondence. The candidate solution only reaches the Pollington–Velani hyperplane threshold α = α_1(μ_K) via the simplex-lemma/absolute-decay route and explicitly cannot upgrade to all α < ϖ. The paper’s argument is coherent: Theorem 2 establishes the needed contraction with exponent α = (ρϖ)/(d+1) (ρ < 1), yielding exponentially recurrent sets; excursion bounds translate to bounds for the minimal vector along the flow; the Dani correspondence plus a change of variables yields the stated summability criterion and conclusion μ_K(ψ-approximable) = 0. While the paper treats Theorem 2 as a black-box import from [Kha20], the remainder is rigorous and correctly assembled. Hence the paper’s result stands, and the candidate’s is strictly weaker.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The paper delivers a clean strengthening of the convergence threshold for metric Diophantine approximation on IFS fractals, moving from the hyperplane exponent to the broader α < ϖ range by bringing in a contraction hypothesis from Khalil and the random-walk/homogeneous-dynamics framework. The dependence on an external black-box (Theorem 2) is standard for the area and plausibly satisfied in the stated setting. The exposition is succinct and technically sound, though a few clarifications would improve self-containment and readability.