  In this paper, we elaborate on a method to decompose multiloop multileg
scattering amplitudes into Lorentz-invariant form factors, which exploits the
simplifications that arise from considering four-dimensional external states.
We propose a simple and general approach that applies to both fermionic and
bosonic amplitudes and allows us to identify a minimal number of physically
relevant form factors, which can be related one-to-one to the independent
helicity amplitudes. We discuss explicitly its applicability to various four-
and five-point scattering amplitudes relevant for LHC physics.
