Transfer principles for Galois cohomology and Serre's conjecture II

Abstract: In this article, we prove several transfer principles for the cohomological dimension of fields. Given a fixed field $K$ with finite cohomological dimension $\delta$, the two main ones allow to: - construct totally ramified extensions of $K$ with cohomological dimension $\leq \delta - 1$ when $K$ is a complete discrete valuation field; - construct algebraic extensions of $K$ with cohomological dimension $\leq \delta-1$ and satisfying a norm condition. We then apply these results to Serre's conjecture II and to some variants for fields of any cohomological dimension that are inspired by conjectures of Kato and Kuzumaki. In particular, we prove that Serre's conjecture II for characteristic $0$ fields implies Serre's conjecture II for positive characteristic fields.