THE GEOMETRY AND ARITHMETIC OF A CALABI–YAU SIEGEL THREEFOLD
Abstract
In this paper we treat in details a Siegel modular variety that has a Calabi–Yau model,
. We shall describe the structure of the ring of modular forms and its geometry. We shall illustrate two different methods of producing the Hodge numbers. The first uses the definition of
as the quotient of another known Calabi–Yau variety
. In this case we will get the Hodge numbers considering the action of the group on a crepant resolution
of
. The second, purely algebraic geometric, uses the equations derived from the ring of modular forms and is based on determining explicitly the Calabi–Yau model
and computing the Picard group and the Euler characteristic.