  BCFW deformation has served as an extremely useful tool in providing a
recursive approach in studying color-ordered gauge amplitudes. This procedure
has also been generalized to the study of graviton scattering. An important
ingredient of this approach is the ability to identify amplitudes satisfying
convergent dispersion relation when the BCFW parameter, z, is treated as a
complex variable. In a modified BCFW treatment, we show in what sense the BCFW
deformation in the large-z limit can be understood as the Regge limit. We also
discuss how the issue of convergent dispersion integral for amplitudes
involving external spins relates to the study of super-convergence relation
which served as the precursor to the s-t duality relation for flat space string
amplitudes.
