The discrete Hankel-transform feasibility conjecture

From papers

Let s{+,}s\in\{+,-\} and ν12\nu\geqslant-\tfrac12. For functions on [q]={1,2,,q}[q]=\{1,2,\ldots,q\}, let Asdisc(q,ν)\mathbb{A}_s^{\textup{disc}}(q,\nu) be the discrete Hankel-transform feasibility constant, and call (k,q)(k,q) (s,ν)(s,\nu)-feasible when an admissible function has ksfkk_{sf}\leqslant k. Let {jn}n1\{j_n\}_{n\geqslant1} be the positive zeros of JνJ_\nu.

Discrete Hankel-transform feasibility conjecture. If (k,q)(k,q) is (s,ν)(s,\nu)-feasible, then (k+1,q)(k+1,q) and (k,q1)(k,q-1) are (s,ν)(s,\nu)-feasible. The function qAsdisc(q,ν)q\mapsto\mathbb{A}_s^{\textup{disc}}(q,\nu) is non-decreasing, and its range contains N[k0]\mathbb{N}\setminus[k_0] for some k01k_0\geqslant1. Moreover, if ν=d21\nu=\tfrac d2-1 and nq=Asdisc(q,ν)n_q=\mathbb{A}_s^{\textup{disc}}(q,\nu), then

limqjnq2πjq+1=As(d),\lim_{q\to\infty}\frac{j_{n_q}}{\sqrt{2\pi j_{q+1}}}=\mathbb{A}_s(d),

where As(d)\mathbb{A}_s(d) is the corresponding continuous sign uncertainty constant.

This is the Hankel-transform analogue of the discrete Fourier-transform conjecture. The source gives numerical support, particularly in dimensions 22, 88, 1212, and 2424, but no general proof.

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Sources & referencesView supporting material

Primary source

Felipe Gonçalves, Diogo Oliveira e Silva and João P. G. Ramos, “New Sign Uncertainty Principles”, arXiv:2003.10771 (2023).

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