Profinite Rigidity over Noetherian Domains

Abstract

We initiate the study of profinite rigidity for modules over a Noetherian domain: to what extent are these objects determined by their finite images? We establish foundational statements in analogy to classical results in the category of groups. We describe three profinite invariants of modules over any Noetherian domain $\hat{I}›$. We show that free modules are profinitely rigid when $\hat{I}›$ satisfies a homological condition, and characterise the profinite genus of all modules when $\hat{I}›$ is a Dedekind domain. In the case where $\hat{I}›$ is a PID, we find that all finitely generated modules are profinitely rigid. As an application, we prove that solvable Baumslag--Solitar groups are profinitely rigid in the absolute sense. These are the first examples of absolute profinite rigidity among non-abelian one-relator groups and among non-LERF groups.

25 pages, comments welcome; version 2 includes the addition of a section on Dedekind domains and the correction of an error in Proposition 5.1 of version 1