Generalised Unitarity At One-Loop With Massive Fermions

We describe an application of generalised unitarity to the computation of one-loop amplitudes with massive external fermions. We present analytic results for the cut-constructible parts of the leading colour contributions to the all-plus helicity configuration of the $t\bar{t}gg$ amplitude. Using a special choice for the helicity basis of the massive fermions we are able to obtain extremely compact analytic expressions. In particular we describe how one can fix the divergent contributions from tadpole and wave-function renormalisation using universal UV and IR behaviour.
Comment: 6 pages, 4 figures, Contribution to the Proceedings of the 9th DESY workshop on "Loops and Legs in Quantum Field Theory", Sondershausen, April 2008