  We bound the coupling of pseudo-scalar particles to Tr G^G_{QCD} using (the
lack of) monojet plus missing E_T events at the Tevatron, and estimate the
bounds obtainable from LHC. In addition, we revisit the bounds on the coupling
to F^F_{EM} from e^+e^- collider events with single photon and missing E_T
final states. This is especially interesting in light of the recent
experimental results from the PVLAS collaboration, which we believe can be
tested by data which will be available in the near future.
