ABSTRACT
This chapter analyses topological properties of nonabelian instantons and solitons and discusses some associated peculiar effects. Non-Abelian gauge theories with any symmetry group G possess topologically nontrivial fields. The most dramatic manifestation of topological effects occurs when one take account of the interaction of massless Dirac fermions with instantons. The chapter shows that instantons lead in this case to violation of some apparent conservation laws. As happened in the case of the n-field, the instanton contribution has an infrared divergence. This implies that in the multi-instanton picture, individual instantons tend to grow and to overlap. The naive dilute gas approximation is certainly inapplicable then, and we should expect something like dissociation of dipole-like instantons to their elementary constituents, as happened in the case of the n-field. However, even one loop computations on the multi-instanton background have not yet been performed, and nothing similar to the Coulomb plasma of the previous section has been discovered.
