Thank you for the response, blechman.
The suppression factor, e^{-8 \pi^{2}/g^{2}}), is usually small, but not so small for SU(3) instantons since the coupling constant is large at low energy.
So if instanton effects are big enough to solve the axial U(1) problem (and the effects are...
It is often said that fermions are protected from large mass corrections by chiral symmetry. My question is does the axial anomaly generate corrections to fermion masses, and if so, doesn't this ruin the protection afforded by chiral symmetry to some extent?
Thanks,
Ben