Generic dilation conjecture for the discrete fractal uncertainty principle

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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∑ℓ=0N−1exp⁡(−2πiαjℓN)u(ℓ).\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⁡(0,12−δ)\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,α1Ck∥CN→CN=O(N−β)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.

References

Primary source

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

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