Instanton Triggered Chiral Symmetry Breaking, the U(1) Problem and a Possible Solution to the Strong CP Problem

Abstract

We argue that instantons play a crucial role in triggering the spontaneous breaking of chiral symmetry in the physics of the three light quarks in quantum chromodynamics. However, instantons may also play an essential role in our understanding of the suppression of CP violation in the strong interactions. We revive the possibility that the bare mass of the up quark is identically zero and the apparent small up quark mass is generated by the effective quark dynamics associated with instantons. In this case, the strong CP phase becomes unobservable and there is no strong CP violation.