Multi-gluon helicity amplitudes with one off-shell leg within high   energy factorization
  Basing on the Slavnov-Taylor identities, we derive a new prescription to obtain gauge invariant tree-level scattering amplitudes for the process g*g->Ng within high energy factorization. Using the helicity method, we check the formalism up to several final state gluons, and we present analytical formulas for the the helicity amplitudes for N=2. We also compare the method with Lipatov's effective action approach. 
Andreas van Hameren, Piotr Kotko, Krzysztof Kutak
hep-ph