Helson's conjecture for smooth numbers

Fuente: arXiv
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Auteurs principaux: Hardy, Seth, Xu, Max Wenqiang
Format: Preprint
Publié: 2025
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author Hardy, Seth
Xu, Max Wenqiang
author_facet Hardy, Seth
Xu, Max Wenqiang
contents Let $Ψ(x,y)$ denote the count of $y$-smooth numbers below $x$ and $P(n)$ denote the largest prime factor of $n$. We prove that for $f$ a Steinhaus random multiplicative function, the partial sums over $y$-smooth numbers always enjoy better than squareroot cancellation, in the sense that $$ \mathbb{E} \Big|\sum_{\substack{1\leq n \leq x\\ P(n) \leq y}} f(n) \Big| = o\left( Ψ(x,y)^{1/2} \right),$$ uniformly on the entire range $ 2 \leq y \leq x$. The bounds are quantitative and give a large saving when $y$ isn't too close to $x$.
format Preprint
id arxiv_https___arxiv_org_abs_2511_03430
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Helson's conjecture for smooth numbers
Hardy, Seth
Xu, Max Wenqiang
Number Theory
Classical Analysis and ODEs
Complex Variables
Functional Analysis
Probability
Let $Ψ(x,y)$ denote the count of $y$-smooth numbers below $x$ and $P(n)$ denote the largest prime factor of $n$. We prove that for $f$ a Steinhaus random multiplicative function, the partial sums over $y$-smooth numbers always enjoy better than squareroot cancellation, in the sense that $$ \mathbb{E} \Big|\sum_{\substack{1\leq n \leq x\\ P(n) \leq y}} f(n) \Big| = o\left( Ψ(x,y)^{1/2} \right),$$ uniformly on the entire range $ 2 \leq y \leq x$. The bounds are quantitative and give a large saving when $y$ isn't too close to $x$.
title Helson's conjecture for smooth numbers
topic Number Theory
Classical Analysis and ODEs
Complex Variables
Functional Analysis
Probability
url https://arxiv.org/abs/2511.03430