Geometric and o-minimal Littlewood-Offord problems

Abstract

The classical Erdős-Littlewood-Offord theorem says that for nonzero vectors $a_1,\dots,a_n\in \mathbb{R}^d$, any $x\in \mathbb{R}^d$, and uniformly random $(ξ_1,\dots,ξ_n)\in\{-1,1\}^n$, we have $\Pr(a_1ξ_1+\dots+a_nξ_n=x)=O(n^{-1/2})$. In this paper we show that $\Pr(a_1ξ_1+\dots+a_nξ_n\in S)\le n^{-1/2+o(1)}$ whenever $S$ is definable with respect to an o-minimal structure (for example, this holds when $S$ is any algebraic hypersurface), under the necessary condition that it does not contain a line segment. We also obtain an inverse theorem in this setting.