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On the Brauer group of an arithmetic model of a variety over a global field of positive characteristic
T. V. Prokhorova A. G. and N. G. Stoletov Vladimir State University, Gorky str., 87, Vladimir, 600000, Russia
Abstract:
Let $V$ be a smooth projective variety over a global field
$k=\kappa(C)$ of rational functions on a smooth projective curve $C$
over a finite field $\Bbb F_q$ of characteristic $p$.
Assume that there is a projective flat $\Bbb F_q$-morphism $\pi:X\to C$,
where $X$ is a smooth projective variety and the generic scheme fiber of $\pi$ is isomorphic to a variety $V$
(we call $\pi:X\to C$ an arithmetic model of a variety $V$).
M. Artin conjectured the finiteness of the Brauer group $\operatorname{Br}(X)$ classifying
sheaves of Azumaya algebras on $X$ modulo similitude. It is well known
that the group $\operatorname{Br}(X)$ is contained in the cohomological Brauer group
$$\operatorname{Br}'(X)=H^2_{et}(X, {\Bbb G}_m).$$
By definition, the $\operatorname{non}-p$ component of the cohomological Brauer group $\operatorname{Br}'(X)$
coincides with the direct sum of the $l$-primary components of the group $\operatorname{Br}'(X)$
for all prime numbers $l$ different from the characteristic $p$. It is known that the structure of $k$-variety on $V$ yields the canonical morphism of the groups
$\operatorname{Br}(k)\to \operatorname{Br}'(V)$.
The finiteness of the $\operatorname{non}-p$ component of the cohomological Brauer group $\operatorname{Br}'(X)$
of a variety $X$ has been proved if $$[\operatorname{Br}'(V)/\operatorname{Im}[\operatorname{Br}(k)\to\operatorname{Br}'(V)]](\operatorname{non}-p)$$ is finite.
In particular, if $V$ is a $\operatorname{K}3$ surface (in other words,
$V$ is a smooth projective simply connected surface over a field $k$
and the canonical class of a surface of $V$ is trivial: $\Omega^2_V=\mathcal O_V$)
and the characteristic of the ground field $p > 2$, then, by the Skorobogatov–Zarhin theorem,
$[\operatorname{Br}'(V)/\operatorname{Im}[\operatorname{Br}(k)\to\operatorname{Br}'(V)]](\operatorname{non}-p)$ is finite,
so in this case the groups $\operatorname{Br}'(X)(\operatorname{non}-p)$ and $\operatorname{Br}(X)(\operatorname{non}-p)$ are finite.
Keywords:
Brauer group, arithmetic model, $\operatorname{K}3$ surface.
Received: 13.02.2016
Citation:
T. V. Prokhorova, “On the Brauer group of an arithmetic model of a variety over a global field of positive characteristic”, Model. Anal. Inform. Sist., 23:2 (2016), 164–172
Linking options:
https://www.mathnet.ru/eng/mais488 https://www.mathnet.ru/eng/mais/v23/i2/p164
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