Let $\mathbb{ F}$ be a finite field and $C,D$ smooth, geometrically irreducible proper curves over $\mathbb{ F}$ and set $K = \mathbb{ F}(D)$. We consider Brauer-Manin and abelian descent obstructions to the existence of rational points and to weak approximation for the curve $C \otimes_\mathbb{ F} K$. In particular, we show that Brauer-Manin is the only obstruction to weak approximation and the Hasse principle in the case that the genus of $D$ is less than that of $C$. We also show that we can identify the points corresponding to non-constant maps $D \to C$ using Frobenius descents.
Categories: math.NT math.AG