Spinor-Helicity Three-Point Amplitudes from Local Cubic Interactions
  We make an explicit link between the cubic interactions of off-shell fields and the on-shell three-point amplitudes in four dimensions. Both the cubic interactions and the on-shell three-point amplitudes had been independently classified in the literature, but their relation has not been made explicit. The aim of this note is to provide such a relation and discuss similarities and differences of their constructions. For the completeness of our analysis, we also derive the covariant form of all parity-odd massless vertices. 
Eduardo Conde, Euihun Joung and Karapet Mkrtchyan
hep-th