Abel-Prym maps for isotypical components of Jacobians

Abstract

Let $C$ be a smooth non rational projective curve over the complex field $\mathbb{C}$. If $A$ is an abelian subvariety of the Jacobian $J(C)$, we consider the Abel-Prym map ${\phi }_A:C\to A$ defined as the composition of the Abel map of $C$ with the norm map of $A$. The goal of this work is to investigate the degree of the map ${\phi }_A$ in the case where $A$ is one of the components of an isotypical decomposition of $J(C)$. In this case we obtained a lower bound for $\mathrm{deg}({\phi }_A)$ and, under some hypotheses, also an upper bound. We then apply the results obtained to compute degrees of Abel-Prym maps in four cases. In particular, these examples show that both bounds are sharp.

Last section changed, more general examples added