arXiv:2006.10821v2

Pure Point Diffraction and Mean, Besicovitch and Weyl Almost Periodicity

Daniel Lenz, Timo Spindeler, Nicolae Strungaru

math.CAmath.FA37A3043A0543A0743A2543A6022D10

Abstract

We show that a translation bounded measure has pure point diffraction if and only if it is mean almost periodic. We then go on and show that a translation bounded measure has pure point diffraction and satisfies the so called consistent phase property if and only if it is Besicovitch almost periodic. Finally, we show that a translation bounded measure has pure point diffraction and satisfies the consistent phase property independent of the underlying van Hove sequence if and only if it is Weyl almost periodic. These results solve fundamental issues in the theory of pure point diffraction and answer questions of Lagarias.

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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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Generated August 18, 2026
01Statements3 reported findingsCorrect

The equivalences between pure point diffraction and mean almost periodicity, consistent phase and Besicovitch almost periodicity, and sequence-independent Fourier data and Weyl almost periodicity are correct in the stated translation-bounded-measure setting.

Theorems 3.18, 4.39, and 5.21Correct

The three almost-periodicity characterizations agree with diffraction data

Chapters 3–5 · Theorems 3.18, 4.39, and 5.21 · arXiv:2006.10821v2

The autocorrelation seminorm realizes mean almost periodicity in the associated Hilbert space, where pure point diffraction is exactly pure point spectral measure. The Fourier–Bohr coefficients and their phases give the Besicovitch reconstruction, while uniformity over van Hove translates upgrades the same argument to the Weyl topology. The consistency and existence hypotheses used in each direction are explicitly retained.

Full monograph, version 2
Theorem 3.18Correct

Pure point diffraction is equivalent to mean almost periodicity

Chapter 3 · Theorem 3.18 · arXiv:2006.10821v2

Convolution against compactly supported test functions embeds the translation-bounded measure into the autocorrelation Hilbert space. The spectral measure of each convolution is the corresponding weighted diffraction measure, so discreteness of diffraction is equivalent to relative compactness of all translation orbits in the mean seminorm.

Theorems 4.39 and 5.21Correct

Phase consistency distinguishes Besicovitch and Weyl reconstruction

Chapters 4–5 · Theorems 4.39 and 5.21 · arXiv:2006.10821v2

The Besicovitch theorem reconstructs the measure from Fourier–Bohr coefficients only after the consistent-phase relations are imposed. The Weyl theorem adds uniformity over translates of the averaging sequence, which makes the coefficients independent of the selected van Hove sequence. The hypotheses and conclusions are kept distinct in the paper.

02Proofs3 reported findingsCorrect

The long proof development is correct and complete; the Hilbert-space, approximation, and Fourier–Bohr arguments cover both implications of the central equivalences.

Chapters 2–5Correct and complete

Seminorm completions and Fourier reconstructions are compatible

Chapters 2–5 · arXiv:2006.10821v2

Translation boundedness supplies all convolution estimates, van Hove boundary terms vanish at the required scales, and the Bessel/Parseval identities are applied only after passing to the relevant seminorm completion. The phase-form construction is used precisely where coefficients alone do not determine the measure.

Chapter 3Correct and complete

The autocorrelation Hilbert-space argument proves both directions

Chapter 3 · mean almost periodicity and diffraction · arXiv:2006.10821v2

The proof first establishes the autocorrelation identity for compactly supported convolutions and then applies the pure-point spectral criterion in the completed mean-seminorm space. Density of the convolution family recovers the measure statement, while translation boundedness controls every boundary term.

Chapters 4–5Correct and complete

The Fourier–Bohr approximation and uniform-translate upgrade are complete

Chapters 4–5 · Besicovitch and Weyl approximation theorems · arXiv:2006.10821v2

Finite trigonometric approximants are constructed with the required phases, Parseval identities control the Besicovitch remainder, and the Weyl seminorm repeats the estimates uniformly over translated averaging sets. The proof does not infer the stronger Weyl conclusion from sequencewise convergence alone.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2006.10821v2
Authors listed
Daniel Lenz, Timo Spindeler, Nicolae Strungaru
Audit date
August 18, 2026
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