Global Prym-Torelli for double coverings ramified in at least 6 points

Abstract

We prove that the ramified Prym map $\mathcal{P}_{g, r}$ which sends a covering $\pi: D \longrightarrow C$ ramified in $r$ points to the Prym variety $P(\pi):=\operatorname{Ker}\left(N m_\pi\right)$ is an embedding for all $r \geq 6$ and for all $g(C)>0$. Moreover, by studying the restriction to the locus of coverings of hyperelliptic curves, we show that $\mathcal{P}_{g, 2}$ and $\mathcal{P}_{g, 4}$ have positive dimensional fibers.