Constraints on Axion Models from $K^+\to\pi^+ a$
  We explore a new class of axion models in which some, but not all, of the left-handed quarks have a Peccei-Quinn symmetry. These models are potentially afflicted by flavour changing neutral currents. We derive the bounds on the Peccei-Quinn symmetry-breaking scale from bounds on the $K^+\to \pi^+ a$ branching ratio, showing that in some cases they are even stronger than the astrophysical ones, but still not strong enough to kill off the models. 
Mark Hindmarsh and Photis Moulatsiotis (Sussex)