On surfaces of general type with p_g=q=1 isogenous to a product of curves

Abstract

A smooth algebraic surface $S$ is said to be \emph{isogenous to a product of unmixed type} if there exist two smooth curves $C, F$ and a finite group $G$, acting faithfully on both $C$ and $F$ and freely on their product, so that $S=(C \times F)/G$. In this paper we classify the surfaces of general type with $p_g=q=1$ which are isogenous to an unmixed product, assuming that the group $G$ is abelian. It turns out that they belong to four families, that we call surfaces of type $I, II, III, IV$. The moduli spaces $\mathfrak{M}_{I}, \mathfrak{M}_{II}, \mathfrak{M}_{IV}$ are irreducible, whereas $\mathfrak{M}_{III}$ is the disjoint union of two irreducible components. In the last section we start the analysis of the case where $G$ is not abelian, by constructing several examples.