On the Prym map of Galois coverings

Abstract

We consider the Prym variety $P\left(\tilde{C}∕C\right)$ associated to a Galois coverings of curves $f:\tilde{C}\to C$ branched at $r$ points. We discuss some properties and equivalent definitions and then consider the Prym map $\mathcal{𝒫}=\mathcal{𝒫}\left(G,g,r\right):R\left(G,g,r\right)\to A_{p,\delta }$ with $\delta$ the type of the polarization. For Galois coverings whose Galois group is abelian and metabelian (nonabelian) we show that the differential of this map at certain points is injective. We also consider the Abel-Prym map $u:\tilde{C}\to P\left(\tilde{C}∕C\right)$ and prove some results for its injectivity. In particular, we show that in contrast to the classical and cyclic case, the behavior of this map here is more complicated. The theories of abelian and metabelian Galois coverings play a substantial role in our analysis and have been used extensively throughout the paper.