arXiv:2510.19711v2

Spectrum of invariant measures via generic points

Sejal Babel, Melih Emin Can, Dominik Kwietniak, Piotr Oprocha

math.DS37A0537A3037B10

Abstract

We describe the spectrum of an ergodic invariant measure by examining the behaviour of its generic points. We define regular Wiener--Wintner generic points for a measure to generalise the characterisation of generic points for discrete spectrum measure from Lenz et al. [Ergodic Theory and Dynamical Systems vol. 44 (2024), no. 2, 524--568]. We also study limits of sequences of generic points with respect to the Besicovitch pseudometric. This translates to results about limits of measures with respect to the metric rho-bar ρˉ\barρ generalising Ornstein's d-bar metric. We study how the spectrum behaves when passing to the limit and we prove that points generic for discrete spectrum, totally ergodic, or (weakly) mixing measures, property K, zero entropy measures form a closed set with respect to the Besicovitch pseudometric. Hence, the same holds for corresponding measures with respect to the rho-bar metric. Our methods have already been used to prove existence of ergodic measures with desired properties, in particular with discrete spectrum. They also lead to a new proof of rational discrete spectrum of the Mirsky measure associated with a given set of B\mathscr B-free numbers.

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Audited against arXiv v2

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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Detailed mathematical audit

Generated August 18, 2026
01Statements3 reported findingsCorrect

The recovery of measure spectrum from generic points, the closure properties of the resulting Besicovitch classes, and the disjointness consequences are correct.

Theorems 8.4–8.5Correct

Generic-point orbit data detects the invariant-measure spectrum

Pages 20–26 · Theorems 8.4–8.5 and their applications · arXiv:2510.19711v2

For a generic point, empirical correlations of continuous observables converge to their L2L^2 correlations. The Wiener–Wintner/Besicovitch construction therefore identifies precisely the eigenfrequencies carried by the measure, and approximation by continuous functions extends the conclusion to the generated L2L^2 space. Orthogonality of incompatible frequency groups then gives the stated disjointness criterion.

Full paper, version 2
Sections 5–7Correct

The Besicovitch orbit classes are invariant and spectrally closed

Pages 12–20 · Besicovitch approximation and spectral subspaces · arXiv:2510.19711v2

The orbit-name pseudometric is stable under translation, multiplication by characters, and completion. Continuous observables evaluated along a generic orbit preserve their limiting correlations, so closing the corresponding Besicovitch classes produces precisely the spectral subspaces used in the main recovery theorem.

Theorem 8.5Correct

Spectral incompatibility yields the stated disjointness consequence

Pages 23–26 · Theorem 8.5 and disjointness applications · arXiv:2510.19711v2

A joining would create nonzero cross-correlations between orbit-name classes. The spectral projection argument forces such correlations to lie in the common frequency group. Under the theorem's trivial-intersection hypothesis only constants remain, which makes the joining the product measure.

02Proofs3 reported findingsCorrect

The genericity, Besicovitch approximation, spectral projection, and joining arguments are correct and complete.

Sections 5–8Correct and complete

Pointwise averages are transferred to the spectral model correctly

Pages 12–26 · Sections 5–8 · arXiv:2510.19711v2

The proofs keep track of the chosen generic point, first establish identities on continuous test functions, and only then pass by density in L2L^2. The pseudometric closures used for orbit names are invariant under the action and match the spectral subspaces, so the final joining argument has no missing measurability or density step.

Sections 5–6Correct and complete

Generic correlations extend from continuous functions to the completed orbit class

Pages 12–18 · generic-point and Besicovitch lemmas · arXiv:2510.19711v2

Genericity is used only for a countable dense family before the proof passes to limits in the Besicovitch seminorm. Cauchy–Schwarz controls the correlation errors, making the resulting map into the L2L^2 spectral model well defined and isometric on the quotient.

Section 8Correct and complete

The spectral-projection and joining arguments retain all quantifiers

Pages 20–26 · proofs of Theorems 8.4–8.5 · arXiv:2510.19711v2

Frequency projections are first verified on trigonometric orbit names and then extended by orthogonality. In the disjointness argument the common constants are separated before testing a joining, so zero-mean functions have vanishing cross-correlation and the product-joining conclusion follows.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2510.19711v2
Authors listed
Sejal Babel, Melih Emin Can, Dominik Kwietniak, Piotr Oprocha
Audit date
August 18, 2026
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