Applications of instantons to hadronic processes

In this thesis we study two processes in which instantons may play an important role: the decays of charmonium states $\eta_c$, $\chi_c$ and glueball and the OZI violation in channels relevant to the proton spin decomposition puzzle. We also present an algorithm for computation of integrals over compact groups and exemplify it on integrals over SU(N) fundamental and adjoint representations.