An exact theory for scattering as a function of angle.
References
Collins, P. D. B. An Introduction to Regge Theory and High-Energy Physics. Cambridge, England: Cambridge University Press, 1977.
Frautschi, S. C. Regge Poles and S-Matrix Theory. New York: W. A. Benjamin, 1963.
Weisstein, E. W. "Books about Regge Poles." http://www.ericweisstein.com/encyclopedias/books/ReggePoles.html.
