The Lorentz Expansion for Scattering Amplitudes

We discuss an expansion of the spinless scattering amplitude $A(s, t, u)$ in terms of the representation coefficients of the Lorentz group. The expansion preserves the cut structure of $A(s, t, u)$ on a term-by-term basis, and is valid for arbitrary values of $s$, $t$, $u$. The expansion parameters are given in terms of Regge trajectory and residue functions.