Eduard Stefanescu

Maximal gap distribution and infinite covering

Let \((a_n)_{n \in \mathbb{N}}\) be a lacunary sequence of integers satisfying the Hadamard gap condition. For any fixed dimension $d \geq 1$, we establish asymptotic upper bounds for the maximal gap in the set of dilates \(\{\boldsymbol{\alpha} a_n \}_{n \leq N}\) modulo 1 as  $N \to \infty$, for Lebesgue--almost all dilation vectors $\boldsymbol{\alpha} \in [0,1]^d$. More precisely, we prove that for any lacunary \((a_n)_{n \in \mathbb{N}}\) and Lebesgue--almost all  $\boldsymbol{\alpha}$, every convex set in $[0,1]^d$ of volume at least $(\log N)^{2}/N$ must contain an element of  the set \(\{\boldsymbol{\alpha} a_n \}_{n \leq N}\) mod 1, for all sufficiently large $N$. We also establish a generalized version of this result, where the $d$-dimensional Lebesgue measure is replaced by a general measure satisfying a certain Fourier decay condition. Our result is optimal up to logarithmic factors, and recovers as a special case a recent result for dimension $d=1$. Finally, we show an improved upper bound in the inhomogeneous version of Littlewood's problem in multiplicative Diophantine approximation.