I will present an outline of recent advances in on-shell methods for the calculation of 1-loop scattering amplitudes relevant QCD and the SM. Working within the framework of colour ordered helicity amplitudes it is possible to construct loop amplitudes from tree level structures using basic complex analysis and universal factorisation properties. I will show how these methods can be used to calculate compact analytic expressions for multi-particle processes involving top quarks and gluons.

SPhT, CEA/Saclay