CSW rules for a massive scalar

Abstract

We derive the analog of the Cachazo-Svrcek-Witten (CSW) diagrammatic Feynman rules for four dimensional Yang-Mills gauge theory coupled to a massive colored scalar. The mass term is shown to give rise to a new tower of vertices in addition to the CSW vertices for massless scalars in non-supersymmetric theories. The rules are derived directly from an action, once through a canonical transformation within light-cone Yang-Mills and once by the construction of a twistor action. The rules are tested against known results in several examples and are used to simplify the proof of on-shell recursion relations for amplitudes with massive scalars.