A polynomial Freiman-Ruzsa inverse theorem for function fields

Abstract

Using the recent proof of the polynomial Freiman-Ruzsa conjecture over $\mathbb{F}_p^n$ by Gowers, Green, Manners, and Tao, we prove a version of the polynomial Freiman-Ruzsa conjecture over function fields. In particular, we prove that if $A\subset\mathbb{F}_p[t]$ satisfies $\lvert A+tA\rvert\leq K\lvert A\rvert$ then $A$ is efficiently covered by at most $K^{O(1)}$ translates of a generalised arithmetic progression of rank $O(\log K)$ and size at most $K^{O(1)}\lvert A\rvert$. As an application we give an optimal lower bound for the size of $A+\xi A$ where $A\subset\mathbb{F}_p((1/t))$ is a finite set and $\xi\in \mathbb{F}_p((1/t))$ is transcendental over $\mathbb{F}_p[t]$.