Raising the axion mass

We present a mechanism which raises the axion mass while maintaining the standard axion-fermion coupling and the removal of strong CP violation. The source of this new contribution to the axion mass is small color SU(3) instantons; these may be important if new physics above the weak interaction scale causes the color coupling constant to grow strong and produces anomalous dimensions for certain many-fermion operators. Strongly interacting hyperquarks may be responsible for both effects. We discuss the working of this mechanism in an explicit hypercolor-sideways interaction model in which a Peccei-Quinn symmetry appears naturally. In this particular model, heavy axion exchange could produce significant D0anti D0 mixing. (orig.)