The Refined Humbert Invariant for Imprimitive Ternary Forms

Abstract: In this paper, we discuss the refined Humbert invariant for abelian product surfaces with complex multiplication. More precisely, we give the classification of quadratic forms which are equivalent to some refined Humber invariant $q_{(A,\theta)},$ where $A$ is isogenous to $E\times E,$ where $E$ has complex multiplication, and $q_{(A,\theta)}$ is an imprimitive form. To give this classification, we use and derive some results in the theory of integral ternary and binary quadratic forms.