  By analytically continuing QCD scattering amplitudes through specific
complexified momenta, one can study and learn about the nature and the
consequences of factorization and unitarity. In some cases, when coupled with
the largest time equation and gauge invariance requirement, this approach leads
to recursion relations, which greatly simplify the construction of multi-gluon
scattering amplitudes. The setting for this discussion is in the space-cone
gauge.
