An effective Lagrangian with no U(1) problem in CP$^{n-1}$ models and QCD

The author writes an effective lagrangian which gives two-point Green's functions satisfying the anomalous Ward identities for the U (1) axial vector current with a singlet particle that has a non- vanishing mass in the chiral limit. It is shown that the mechanism that has been postulated by Witten (1979) and Veneziano (1979) for solving the U(1) problem in the framework of the 1/n expansion in QCD is fully active in the two-dimensional CP/sup n-1/ model where the 1/n expansion can be explicitly performed. (6 refs).