Undecidability of infinite algebraic extensions of ${\mathbb{F}}_p(t)$

Abstract

Building on work of J. Robinson and A. Shlapentokh, we develop a general framework to obtain definability and decidability results of large classes of infinite algebraic extensions of ${\mathbb{F}}_p(t)$. As an application, we show that for every odd rational prime $p$ there exist infinitely many primes $r$ such that the fields ${\mathbb{F}}_{p^a}\left(t^{r^{-\infty }}\right)$ have undecidable first-order theory in the language of rings without parameters. Our method uses character theory to construct families of non-isotrivial elliptic curves whose Mordell-Weil group is finitely generated and of positive rank in ${\mathbb{Z}}_r$-towers.

28 pages