On axion-mediated macroscopic forces again

In a supersymmetric unified theory or in a generic model where a large neutron electric dipole moment d(N) is expected, close to the present bound, we estimate the relation g(aNN) = 10(-21+/-1)(d(N)/10(-25)e . cm) (10(10) GeV/f(a)) between d(N) itself, the scalar coupling g(aNN) to nucleons of the axion, assumed to exist, and the breaking scale, f(a), of the Peccei-Quinn symmetry. Newly developing techniques to search for sub-cm macroscopic forces might reveal a signal due to axion exchange at least in a favorable range of f(a).