On a Restriction Problem of Hickman and Wright for the Parabola in $\mathbb{Z}/N\mathbb{Z}$ for Squarefree $N$

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Auteur principal: Kingsbury-Neuschotz, Nathaniel
Format: Preprint
Publié: 2025
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author Kingsbury-Neuschotz, Nathaniel
author_facet Kingsbury-Neuschotz, Nathaniel
contents Hickman and Wright proved an $L^2$ restriction estimate for the parabola $Σ$ in $\mathbb{Z}/N\mathbb{Z}$ of the form $$\left(\frac{1}{|Σ|}\sum\limits_{m\inΣ}|\widehat{f}(m)|^2 \right)^{\frac{1}{2}}\leq C_εN^ε\cdot N^{-1}\left(\sum\limits_{x\in (\mathbb{Z}/N\mathbb{Z})^2}|f(x)|^\frac{6}{5}\right)^\frac{5}{6}$$ for all functions $f:(\mathbb{Z}/N\mathbb{Z})^2\rightarrow \mathbb{C}$ and any $ε>0$, and that this bound is sharp when $N$ has a large square factor, and especially for $N = p^2$ for $p$ a prime. In contrast, Mockenhaupt and Tao proved in the special case $N = p$ the stronger estimate $$\left(\frac{1}{|Σ|}\sum\limits_{m\inΣ}|\widehat{f}(m)|^2 \right)^{\frac{1}{2}}\leq C N^{-1}\left(\sum\limits_{x\in (\mathbb{Z}/N\mathbb{Z})^2}|f(x)|^\frac{4}{3}\right)^\frac{3}{4}.$$ We extend the Mockenhaupt-Tao bound to the case of squarefree $N$, proving $$\left(\frac{1}{|Σ|}\sum\limits_{m\inΣ}|\widehat{f}(m)|^2 \right)^{\frac{1}{2}}\leq C_εN^ε\cdot N^{-1}\left(\sum\limits_{x\in (\mathbb{Z}/N\mathbb{Z})^2}|f(x)|^\frac{4}{3}\right)^\frac{3}{4},$$ and discuss applications of this result to uncertainty principles and signal recovery.
format Preprint
id arxiv_https___arxiv_org_abs_2509_09885
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle On a Restriction Problem of Hickman and Wright for the Parabola in $\mathbb{Z}/N\mathbb{Z}$ for Squarefree $N$
Kingsbury-Neuschotz, Nathaniel
Classical Analysis and ODEs
Combinatorics
Number Theory
Hickman and Wright proved an $L^2$ restriction estimate for the parabola $Σ$ in $\mathbb{Z}/N\mathbb{Z}$ of the form $$\left(\frac{1}{|Σ|}\sum\limits_{m\inΣ}|\widehat{f}(m)|^2 \right)^{\frac{1}{2}}\leq C_εN^ε\cdot N^{-1}\left(\sum\limits_{x\in (\mathbb{Z}/N\mathbb{Z})^2}|f(x)|^\frac{6}{5}\right)^\frac{5}{6}$$ for all functions $f:(\mathbb{Z}/N\mathbb{Z})^2\rightarrow \mathbb{C}$ and any $ε>0$, and that this bound is sharp when $N$ has a large square factor, and especially for $N = p^2$ for $p$ a prime. In contrast, Mockenhaupt and Tao proved in the special case $N = p$ the stronger estimate $$\left(\frac{1}{|Σ|}\sum\limits_{m\inΣ}|\widehat{f}(m)|^2 \right)^{\frac{1}{2}}\leq C N^{-1}\left(\sum\limits_{x\in (\mathbb{Z}/N\mathbb{Z})^2}|f(x)|^\frac{4}{3}\right)^\frac{3}{4}.$$ We extend the Mockenhaupt-Tao bound to the case of squarefree $N$, proving $$\left(\frac{1}{|Σ|}\sum\limits_{m\inΣ}|\widehat{f}(m)|^2 \right)^{\frac{1}{2}}\leq C_εN^ε\cdot N^{-1}\left(\sum\limits_{x\in (\mathbb{Z}/N\mathbb{Z})^2}|f(x)|^\frac{4}{3}\right)^\frac{3}{4},$$ and discuss applications of this result to uncertainty principles and signal recovery.
title On a Restriction Problem of Hickman and Wright for the Parabola in $\mathbb{Z}/N\mathbb{Z}$ for Squarefree $N$
topic Classical Analysis and ODEs
Combinatorics
Number Theory
url https://arxiv.org/abs/2509.09885