Brauer groups and \'etale homotopy type

TL;DR

This paper investigates how the étale homotopy type influences the surjectivity of the Brauer map in algebraic schemes, extending previous results and applying properties of algebraic $K( ext{pi}, 1)$ spaces.

Contribution

It establishes the dependence of the Brauer map's surjectivity on étale homotopy type and introduces conditions involving pro-universal covers, unifying them for smooth quasi-projective varieties.

Findings

Surjectivity of the Brauer map depends on étale homotopy type.

Results recover known cases for abelian varieties.

Provides new conditions involving pro-universal covers.

Abstract

Extending a result of Schr\"oer on a Grothendieck question in the context of complex analytic spaces, we prove that the surjectivity of the Brauer map $\delta: Br(X) \rightarrow H_{\rm \'et}^2(X,\mathbb{G}_{m, X})_{\rm tor}$ for algebraic schemes depends on their \'etale homotopy type. We use properties of algebraic $K(\pi, 1)$ spaces to apply this to some classes of proper and smooth algebraic schemes. In particular we recover a result of Hoobler and Berkovich for abelian varieties. Further, we give an additional condition for the surjectivity of $\delta$ which involves pro-universal covers. All proposed conditions turn out to be equivalent for smooth quasi-projective varieties.