On varieties whose universal cover is a product of curves

Abstract

We investigate a necessary condition for a compact complex manifold X of dimension n in order that its universal cover be the Cartesian product $C^n$ of a curve $C = \PP^1 or \HH$: the existence of a semispecial tensor $\omega$. A semispecial tensor is a non zero section $0\ne \omega \in H^0(X,S^n{\Omega }_X^1(-K_X)\otimes \eta )$), where $\eta$ is an invertible sheaf of 2-torsion (i.e., $η^2\cong \hol_X$). We show that this condition works out nicely, as a sufficient condition, when coupled with some other simple hypothesis, in the case of dimension $n=2$ or $n=3$; but it is not sufficient alone, even in dimension 2. In the case of Kähler surfaces we use the above results in order to give a characterization of the surfaces whose universal cover is a product of two curves, distinguishing the 6 possible cases.

22 pages, dedicated to Sommese's 60-th birthday. Greatly improves, expands and supersedes arXiv:0803.3008, of which also corrects a mistake