Generic dilation conjecture for the discrete fractal uncertainty principle

Fix an integer base MM and alphabet A\mathcal A with 0<δ<10<\delta<1, let Ck\mathcal C_k be the associated discrete Cantor set, and put N=MkN=M^k. For α[1,M]\alpha\in[1,M], define the dilated Fourier transform by

FN,αu(j)=1N=0N1exp(2πiαjN)u().\mathcal F_{N,\alpha}u(j)=\frac1{\sqrt N}\sum_{\ell=0}^{N-1}\exp\left(-\frac{2\pi i\alpha j\ell}{N}\right)u(\ell).

Generic dilation conjecture. There exists β>max(0,12δ)\beta>\max(0,\frac12-\delta) depending only on δ\delta such that, for a generic choice of α[1,M]\alpha\in[1,M],

1CkFN,α1CkCNCN=O(Nβ)as k.\|\mathbf 1_{\mathcal C_k}\mathcal F_{N,\alpha}\mathbf 1_{\mathcal C_k}\|_{\mathbb C^N\to\mathbb C^N}=\mathcal O(N^{-\beta})\quad\text{as }k\to\infty.

A generic dilation is conjectured to improve the elementary discrete FUP exponent uniformly in the base and alphabet, whereas the undilated exponent can be arbitrarily close to the elementary bound.

Sources & referencesView supporting material

Primary source

Semyon Dyatlov, “An introduction to fractal uncertainty principle”, arXiv:1903.02599 (2019).

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