Pfaffian of Appell's hypergeometric system $F_4$ in terms of the intersection form of twisted cohomology groups

Yoshiaki Goto, Jyoichi Kaneko, Keiji Matsumoto

We study a Pfaffian of the system of differential equations annihilating Appell's hypergeometric series $F_4(a,b,c;x)$ by twisted cohomology groups associated with integrals repres…