A finiteness theorem for the Brauer group of abelian varieties and K3 surfaces

Abstract

Let $k$ be a field that is finitely generated over the field of rational numbers and $Br(k)$ the Brauer group of $k$. Let $X$ be an absolutely irreducible smooth projective variety over $k$, let $Br(X)$ be the cohomological Brauer-Grothendieck group of $X$ and $B{r}_0(X)$ the image of $Br(k)$ in $Br(X)$. We write $B{r}_1(X)$ for the subgroup of elements in $Br(X)$ that become trivial after replacing $k$ by its algebraic closure. We prove that $Br(X)/B{r}_0(X)$ is finite if $X$ is a $K3$ surface. When $X$ is (a principal homogeneous space of) an abelian variety over $k$ then we prove that $Br(X)/B{r}_1(X)$ is finite.

20 pages Final version; to appear in the Journal of Algebraic Geometry