Renormalized Ward identities and Callan-Symanzik equations are developed for vertex functions involving composite fields in a massive Thirring model with $\mathrm{U}\mathrm{}\left(n\right)\mathrm{}$ symmetry. The existence of a critical curve of fixed points of a renormalization group acting on a space of coupling constants is proved. On this curve all nonsoft axial-vector and scaling anomalies vanish. Attraction properties of this curve are investigated. The possibility of a second critical curve for strong coupling is discussed.

• Received 13 August 1973

DOI:https://doi.org/10.1103/PhysRevD.8.4410