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Fractal Harmonic Waves: Resolving Fuglede's Conjecture for Cantor-Moran Spectral Measures

Bent Fuglede conjectured in 1974 that a geometric domain can support an orthogonal basis of exponential waves if and only if it can tile space; this mathematical proof confirms the generalized conjecture holds for a broad class of fractal Cantor-Moran measures.

Author
Li-Xiang An et al.
Published
2025
Journal
Pacific Journal of Mathematics
Last updated
September 2026
Fractal Harmonic Waves: Resolving Fuglede's Conjecture for Cantor-Moran Spectral Measures

In harmonic analysis, the fundamental question of Fourier duality asks: which geometric domains allow complex functions to be decomposed into orthogonal sets of pure harmonic waves?

Fuglede's conjecture posited a beautiful equivalence between spectrality (supporting an orthogonal Fourier basis) and tiling (covering space without gaps or overlaps). While the conjecture famously failed for general Euclidean dimensions, its behavior on singular fractal measures remained an open frontier.

This work establishes that the generalized Fuglede conjecture holds rigorously for a significant class of fractal Cantor-Moran measures, proving that spectral properties in these self-similar structures are intrinsically linked to admissible geometric translation tilings.

This mathematical breakthrough deepens our understanding of wave propagation in irregular fractal media, offering analytical foundations for quantum wave mechanics in disordered systems and fractal signal processing.

Reference

An, L.-X., Li, Q., & Zhang, M.-M. (2025). The generalized Fuglede’s conjecture holds for a class of Cantor–Moran measures. Pacific Journal of Mathematics, 334(2), 189–209.

Title

The generalized Fuglede’s conjecture holds for a class of Cantor–Moran measures

Abstract

Suppose b={bn}n=1∞{\bf b}=\{b_n\}_{n=1}^{\infty} is a sequence of integers bigger than 1 and D={Dn}n=1∞{\bf D}=\{{\mathcal D}_{n}\}_{n=1}^{\infty} is a sequence of consecutive digit sets. Let μb,D\mu_{{\bf b},{\bf D}} be the Cantor-Moran measure defined by μb,D=δ1b1D1∗δ1b1b2D2∗δ1b1b2b3D3∗⋯ .\begin{aligned}\mu_{{\bf b},{\bf D}}&=&\delta_{\frac{1}{b_1}{\mathcal D}_{1}}\ast\delta_{\frac{1}{b_1b_2}{\mathcal D}_{2}}\ast \delta_{\frac{1}{b_1b_2b_3}{\mathcal D}_{3}}\ast\cdots.\end{aligned} We prove that L2(μb,D)L^2(\mu_{{\bf b},{\bf D}}) possesses an exponential orthonormal basis if and only if μb,D∗ν=L[0,N1/b1]\mu_{{\bf b},{\bf D}}\ast\nu={\mathcal L}_{[0,N_1/b_1]} for some Borel probability measure ν\nu. This theorem shows that the generalized Fuglede's conjecture is true for such Cantor-Moran measure. An immediate consequence of this result is the equivalence between the existence of an exponential orthonormal basis and the integral tiling of Dn=Dn+bnDn−1+b2⋯bnD1{\bf D}_n={\mathcal D}_{n}+b_n{\mathcal D}_{n-1}+b_2\cdots b_n{\mathcal D}_{1} for n≥1n\geq1.

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