Ferretti-Rajeev term and homotopy theory

We reduce Ferretti-Rajeev models to the usual sigma models with Chern-Simons terms (-terms), and show that whether is quantized or not corresponds to the fact ₄(G _j,n )₃(U(j))= or 0 of the topology in the process of our reduction. We also reconsider the topological invariance of the Chern classes in the language of the field theory.Partially supported by the Grant-in-Aid for Scientific Research, No. 04640088