On scale symmetry in gauge theories
  Buchholz and Fredenhagen proved that particles in the vacuum sector of a scale invariant local quantum field theory do not scatter. More recently, Weinberg argued that conformal primary fields satisfy the wave equation if they have nonvanishing matrix elements between the vacuum and one-particle states. These results do not say anything about actual candidates for scale invariant models, which are nonconfining Yang-Mills theories with no one-particle states in their vacuum sector. The BRST quantization of gauge theories is based on a state space with an indefinite inner product, and the above-mentioned results do not apply to such models. However, we prove that, under some assumptions, the unobservable basic fields of a scale invariant Yang-Mills theory also satisfy the wave equation. In ordinary field theories, particles associated with such a dilation covariant hermitian scalar field do not interact with each other. In the BRST quantization of gauge theories, there is no such triviality result. 
Szilard Farkas
hep-th math-ph math.MP