A Fourier-analytic Uniqueness Theorem for Lattice-point Enumerators

Abstract

We consider a bounded set $P\subset {\mathbb{R}}^d$ and the lattice-point enumerator $L_P(t)=|tP\cap {\mathbb{Z}}^d|$ for real $t>0$. We show that if two bounded measurable sets with boundary of measure zero have the same real-parameter lattice-point enumerators for all integer translates, then their indicator functions agree almost everywhere. As a corollary, any convex body is uniquely determined by this data. Our proof is short and Fourier-analytic, where the key device is a periodic point-counting function whose Fourier coefficients recover the Fourier transform of the indicator function on a dense set. This recovers and extends, with a unified argument, the uniqueness results for rational polytopes and symmetric convex bodies established by Royer [arXiv:1712.01973, arXiv:1712.03937], whose proofs relied on intricate case-specific geometric constructions.

4 pages