Torelli groups and Jacobian varieties of non-orientable compact Klein surfaces

Abstract

The Torelli group of a compact non-orientable Klein surface is the subgroup of the modular group consisting of the mapping classes that act trivially on the first homology group of the surface. We prove that if a surface has genus at least $3$, then the Torelli group acts fixed points free on the Teichmüller space of the surface. That gives an embedding of the Torelli space of a Klein surface in the Torelli space of its complex double. We also construct real tori associated to Klein surfaces, which we call the Jacobian of the surface. We prove that this Jacobian is isomorphic to a component of the real part of the Jacobian of the complex double.