A Weil class is a Hodge cycle arising from the determinant construction for an abelian variety with a balanced
imaginary-quadratic action. If has dimension
and an imaginary
quadratic field
acts compatibly with a polarization with signature
, the determinant space
gives a two-dimensional rational space of
classes of type
in
. These classes need not be
generated by divisor classes.
The associated Hermitian form is hyperbolic when it contains a totally isotropic -dimensional
-subspace.