In this paper, we prove the functional equations for the zeta functions in two variables associated with prehomogeneous vector spaces acted on by maximal parabolic subgroups of orthogonal groups. Moreover, applying the converse theorem of Weil type, we show that elliptic modular forms of integral or half integral weight can be obtained from the zeta functions.
"Modular forms arising from zeta functions in two variables attached to prehomogeneous vector spaces related to quadratic forms." Nagoya Math. J. 175 1 - 37, 2004.