Birational and $\mathbf{A}^1$-invariant lattices in the cohomology of the structure sheaf over non-archimedean fields

TL;DR

The paper develops an $ extbf{A}^1$-invariant cohomology theory for schemes over non-archimedean fields, revealing new properties of automorphism groups and cohomological invariants in algebraic geometry.

Contribution

It introduces an $ extbf{A}^1$-invariant cohomology theory with lattice values for schemes over non-archimedean fields, extending previous work to positive characteristic and non-proper schemes.

Findings

Automorphism groups act quasi-unipotently on cohomology in dimension up to 3.

Refined cohomology theory applies to both characteristic zero and positive characteristic fields.

Construction relies on a variant of tame cohomology and rigid analytic geometry techniques.

Abstract

We show that the cohomology of the structure sheaf of smooth and proper schemes over a complete non-archimedean field $K$ of characteristic zero, can be refined to an $\mathbf{A}^1$-invariant cohomology theory of smooth (not necessarily proper) schemes over $K$ with values in $\mathcal{O}_K$-lattices, and the same holds for $K$ of positive characteristic in dimensions at most $3$. As one application, we obtain that the automorphism group of the function field of a proper smooth variety $X$ of dimension at most 3 over a field of positive characteristic acts quasi-unipotently on the cohomology of the structure sheaf of $X$. The construction of the lattices relies on a variant of the tame cohomology of H\"ubner--Schmidt with coefficients in a twisted version of the tame structure sheaf and uses results from rigid analytic geometry on the cohomology of twisted integral rigid structure sheaves due to Bartenwerfer and van der Put.