The Feynman-like series proposed by Kikkawa, Sakita, and Virasoro, and based on duality, is considered for the planar diagrams of the five-point function. The "Born" term for this series is the Bardakci-Ruegg amplitude. It is found, by summing the series in the appropriate limit, that the amplitude has double-Regge behavior with the same coupling function as the Born term. Each output Regge trajectory is, however, modified by a correction term identical to that obtained for the four-point function and containing the correct elastic threshold. We indicate how this correction term arises by requiring, in analogy with perturbation theory, that the Born term of the four-point function (the Veneziano amplitude) satisfies elastic unitarity.

• Received 8 July 1969

DOI:https://doi.org/10.1103/PhysRev.188.2223