Translating between NIP integral domains and topological fields

Abstract

We prove that definable ring topologies on NIP fields are closely connected to NIP integral domains. More precisely, we show that up to elementary equivalence, any NIP topological field arises from an NIP integral domain. As an application, we prove several results about definable ring topologies on NIP fields, including the following. Let $K$ be an NIP field or expansion of a field. Let $\tau$ be a definable ring topology on $K$. Then $\tau$ is a field topology, and $\tau$ is locally bounded. If $K$ has characteristic $p$ or finite dp-rank, then $\tau$ is "generalized t-henselian" in the sense of Dittman, Walsberg, and Ye, meaning that the implicit function theorem holds for polynomials. If $K$ has finite dp-rank, then $\tau$ must be a topology of "finite breadth" (a $W_n$-topology). Using these techniques, we give some reformulations of the conjecture that NIP local rings are henselian.