Published online by Cambridge University Press: 20 November 2018
We consider Tate cycles on an Abelian variety $A$ defined over a sufficiently large number field
$K$ and having complexmultiplication. We show that there is an effective bound
$C\,=\,C(A,\,K)$ so that to check whether a given cohomology class is a Tate class on
$A$, it suffices to check the action of Frobenius elements at primes
$v$ of norm
$\le \,C$. We also show that for a set of primes
$v$ of
$K$ of density 1, the space of Tate cycles on the special fibre
${{A}_{v}}$ of the Néron model of
$A$ is isomorphic to the space of Tate cycles on
$A$ itself.