The Physics of Instantons in the pseudoscalar and vector meson mixing

When the theory of Quantum Chromodynamics was introduced, it was to explain the observed phenomena of quark confinement and scaling. It was then discovered that the emergence of instantons is an essential consequence of this theory. This led to unanticipated explanations not only for the anomalously high masses of the $eta$ and the $eta$ particles, but also for the remarkable differences that had been observed in the mixing angles for the pseudoscalar mesons and the vector mesons.