ON THE STRONG CP PROBLEM

We show that two well-known solutions to the strong CP problem, the axion and a massless quark, may be understood in terms of the mechanism recently proposed by Samuel where long-range interactions between topological charges may be responsible for the removal of CP violation. We explain how the axion and a QCD meson (identified as the eta' if all quarks are massless) suppress fluctuations in global topological charge by almost identical dynamics although the masses, couplings and relevant length scales are very different. Furthermore, we elucidate the precise origin of the eta'-mass.