English

A better comparison of cdh- and ldh-cohomologies

Algebraic Geometry 2020-03-18 v2

Abstract

In order to work with non-Nagata rings which are Nagata "up-to-completely-decomposed-universal-homeomorphism", specifically finite rank hensel valuation rings, we introduce the notions of pseudo-integral closure and pseudo-normalisation. We use this notion to give a much more direct and shorter proof that Hcdhn(X,F)=Hldhn(X,F)H^n_{cdh}(X, F) = H^n_{ldh}(X, F) for homotopy sheaves FF of modules over the Z(l)\mathbb{Z}_{(l)}-linear motivic Eilenberg-Maclane spectrum. This comparison is an alternative to the first half of the authors volume Ast\'erisque 391, whose main theorem is a cdh-descent result for Voevodsky motives. The motivating new insight is really accepting that Voevodsky's motivic cohomology (with Z[1/p]\mathbb{Z}[1/p]-coefficients) is invariant not just for nilpotent thickenings, but for all universal homeomorphisms.

Keywords

Cite

@article{arxiv.1807.00158,
  title  = {A better comparison of cdh- and ldh-cohomologies},
  author = {Shane Kelly},
  journal= {arXiv preprint arXiv:1807.00158},
  year   = {2020}
}

Comments

Main theorem hypothesis (G1) or (G2) changed to (G1) *and* (G2). Proof remains essentially the same