Helicity amplitudes for high-energy scattering
  We present a prescription to calculate manifestly gauge invariant tree-level helicity amplitudes for arbitrary scattering processes with off-shell initial-state gluons within the kinematics of high-energy scattering. We show that it is equivalent to Lipatov's effective action approach, and show its computational potential through numerical calculations for scattering processes with several particles in the final state. 
A. van Hameren, P. Kotko and K. Kutak
hep-ph hep-th