Sumsets as unions of sumsets of subsets

TL;DR

This paper demonstrates that sumsets in finite vector spaces can be decomposed into unions of smaller sumsets with bounded size, extending recent bounds on sum-free sets using advanced combinatorial and algebraic methods.

Contribution

It introduces a new decomposition technique for sumsets in finite fields, combining the Croot-Lev-Pach and Ellenberg-Gijswijt methods with Meshulam's result on low-rank matrices.

Findings

Sumsets can be expressed as unions of smaller sumsets with bounded size.

The bounds depend exponentially on the dimension, with a base less than q.

The approach generalizes recent bounds on sum-free sets.

Abstract

Let $S$ and $T$ be subsets of $\mathbf{F}_q^n$. We show there are subsets $S'$ of $S$ and $T'$ of $T$ such that $S+T$ is the union of $S+T'$ and $S'+T$, with $|S'| + |T'|$ bounded by $c^n$ with $c < q$. The proof relies on the method of Croot-Lev-Pach and Ellenberg-Gijswijt on the cap set problem, together with a result of Meshulam on linear spaces of low-rank matrices. The result is a modest generalization of the recent bounds on (single-colored and multi-colored) sum-free sets by the author and others.