Evaluating the tame Brauer group of open varieties over local fields

Abstract

In this document we let $U$ be a smooth variety of pure dimension $d$ over a local field $k_v$ with unit ball ${\mathcal{O}}_v$ and residue field $\mathbb{F}$ of characteristic $p>0$ and we set $n$ to be a positive integer such that $p\nmid n$. For various $u\in U(k_v)$ we study the evaluation map $u^{\ast }:{\mathrm{H}}^2(U,{\mu }_n)\to {\mathrm{H}}^2(k_v,{\mu }_n)$. We suppose that $U$ embeds as an open subscheme in a regular scheme $\mathcal{X}$ that is of finite type over ${\mathcal{O}}_v$. We assume that $Z:=\mathcal{X}\setminus U$ is a divisor and we endow it with its reduced scheme structure. We show that for $u_1,u_2\in U(k_v)$ that lift to $x_1,x_2\in \mathcal{X}({\mathcal{O}}_v)$ we obtain the same evaluation map $u_1^{\ast }=u_2^{\ast }$ under the two conditions that first, there is an equality of reductions $\overline{x_1}=\overline{x_2}$ in $\mathcal{X}(\mathbb{F})$ and second, that $\mathrm{cl}(x_1\cap Z)=\mathrm{cl}(x_2\cap Z)$ holds in ${\mathrm{H}}_{|\overline{x}|}^{2d}(Z,{\mu }_n^{\otimes d})$.

16 pages, comments welcome!