arXiv:2606.13270v1

Metric mean dimension of amenable group actions: localization and non-uniformity

Xinyao He, Guohua Zhang, Ruifeng Zhang

math.DS37A3537B05

Abstract

In this paper, we extend Tsukamoto's recent localization formula for metric mean dimension to actions of countable discrete amenable groups, which previously applied only to Rk\mathbb{R}^k- and Zk\mathbb{Z}^k-actions -- by proving that the global metric mean dimension is characterized by the asymptotic entropy of pointwise ε\varepsilon-stable sets (Theorem 2.3). To achieve this generalization, we introduce equivalent definitions of the invariant using topological entropy, packing topological entropy, and Bowen's dimensional entropy, respectively. A key technical contribution is our replacement of tiling arguments with Lindenstrauss's combinatorial covering lemma, which enables us to handle the general structure of amenable groups. Furthermore, we resolve all three questions regarding uniformity raised in Section 6 of a recent paper by Yang, Chen, and Zhou by constructing counterexamples (Theorem 2.6 and Proposition 5.8), which demonstrates that the supremum and limit superior in the localization formula cannot generally be interchanged, thereby highlighting the heterogeneous nature of the convergence. These results clarify the uniformity issue and offer insights into the link between local dynamics and global invariants, while our equivalent definitions provide flexible tools for computing metric mean dimension in concrete settings.

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Audited against arXiv v1

Not a correctness certificate. A “Correct” result may include yellow typos or minor formal corrections that do not affect substantive soundness. It means this audit found no unresolved substantive error under the stated criteria; it does not replace expert scrutiny or formal verification.

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Generated August 18, 2026
01Statements2 reported findingsCorrect

The equivalence and localization formulas for metric mean dimension of amenable-group actions, their extension to arbitrary Følner sequences, and the non-uniformity examples are correct.

Theorems 2.1, 2.3, and 4.4Correct

Global metric mean dimension is correctly localized to pointwise stable sets

Pages 4–5 and 17–20 · localization theorems · arXiv:2606.13270v1

The amenable covering proposition replaces the regular tilings used in the abelian special cases and gives a uniform bound on orbit-ball covers from local Bowen entropy. This proves the difficult global-to-local inequality; the reverse inequality is immediate from inclusion. Equivalence of topological, packing, and Bowen versions follows from the nested-cover argument. Passing to a tempered subsequence is legitimate because the global invariant is Følner-sequence independent and local entropy is monotone under subsequences.

Theorem 2.6 and Proposition 5.8Correct

The product examples separate all four internal and external limits

Pages 5–6 and 21–33 · construction and dimension calculation · arXiv:2606.13270v1

The first shift factor contributes the fixed unit term to the internal quantities while its pointwise stable-set contribution vanishes externally. The sparse-coordinate factor is chosen with prescribed upper and lower densities bb and aa. The product covering inequalities give matching upper and lower bounds, yielding 1+b1+b, 1+a1+a, bb, and aa exactly, and the same calculation applies to the preimage and asymptotic variants.

02Proofs2 reported findingsCorrect

The Lindenstrauss covering argument and the explicit product construction supply complete proofs of the localization and non-uniformity results.

Proposition 4.1Correct and complete

The amenable covering estimate has the required uniformity

Pages 13–17 · key covering proposition · arXiv:2606.13270v1

The temperedness and growth hypotheses are used exactly where the Lindenstrauss covering lemma and the negligible combinatorial overhead require them. The selected orbit pieces cover a fixed proportion, the uncovered remainder is iterated away, and the entropy weights sum with the announced exponential bound. The later subsequence theorem explicitly removes those hypotheses for arbitrary Følner sequences.

Section 5Correct and complete

The stable-set and product-dimension computations match on both sides

Pages 21–33 · arXiv:2606.13270v1

The construction identifies each stable set before computing its covering entropy, and the prescribed-density subsets are used through exact limsup and liminf formulas. Product separated sets give the lower estimates and product covers give the reverse estimates, so none of the four displayed values rests on a one-sided bound.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2606.13270v1
Authors listed
Xinyao He, Guohua Zhang, Ruifeng Zhang
Audit date
August 18, 2026
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