A Counterexample to Wooley's $L^1$ Question for Beatty Sequences

Abstract

For real numbers $α$ and $β$, let $\mathcal{B}(α,β)=\{\lfloorαm+β\rfloor:m\in\mathbb{N}\}$. Wooley asked whether the exponential sum over $\mathcal{B}(α,β)\cap[1,N]$ always has $L^1$ norm $O_{α,β}(\log N)$. We give a negative answer. We construct fixed $α>1$ and $β$, with $1/α$ of finite Diophantine type, such that the $L^1$ norm is $\gg(\log N)^2$ for infinitely many $N$. Wooley also proved that this $L^1$ norm is $O_{α,β}((\log(2N))^2)$ when $1/α$ has finite Diophantine type. Our example shows that his upper bound is sharp.