| Instantons constitute an important part of QCD as they provide a way to reach beyond the perturbative region. In the introductory chapters we present the ideas that constitute the backbone of instanton computation on a simple standard integral. We then turn our attention to QCD instantons and briefly show the steps to compute the effective lagrangian.; The effective lagrangian is then used as a main tool for studying instanton contributions to hadronic decays of the scalar glueball, the pseudoscalar charmonium state etac, and the scalar charmonium state chic. Hadronic decays of the eta c are of particular interest. The three main decay channels are KK¯pi, etapipi and eta'pipi, each with an unusually large branching ratio of ∼5%. We show that the total decay rate into three pseudoscalar mesons can be reproduced using an instanton size distribution consistent with phenomenology and lattice results. Instantons correctly reproduce the ratio B(etapipi)/ B(eta'pipi) but over-predict the ratio B(KK¯pi)/B(etapipi).; In the next part we study the contribution of instantons to OZI violation in the axial-vector channel. We consider, in particular, the f1-a 1 meson splitting, the flavor singlet and triplet axial coupling of a constituent quark, and the axial coupling constant of the nucleon. Instantons provide a short distance contribution to OZI violating correlation functions which is repulsive in the f1 meson channel and adds to the flavor singlet three-point function of a constituent quark. We compute long distance contributions using numerical simulations of the instanton liquid. We find that the iso-vector axial coupling constant of a constituent quark is (g A3)Q = 0.9 and that of a nucleon is g A3 = 1.28, in good agreement with experiment. The flavor singlet coupling of quark is close to one, while that of a nucleon is suppressed gA0 = 0.8. This number is still significantly larger than the experimental value gA0 = (0.28--0.41).; In the last part we present an algorithm for computation of integrals over compact groups and exemplify it on integrals over SU(N) fundamental and adjoint representation. |
