CP violation in gauge theories
  We define the CP transformation properties of scalars, fermions and vectors in a gauge theory and show that only three types of interactions can lead to CP violation: scalar interactions, fermion-scalar interactions and $ F \tilde F $ associated with the strong CP problem and which involve only the gauge fields. For technicolor theories this implies the absence of CP violation within perturbation theory. 
Martin B. Einhorn and Jose Wudka