Thirring model with U(n) symmetry: Scale invariant only for fixed values of a coupling constant

Generalizations of the Thirring model to Fermi fields with U(n) symmetry are treated. When interactions quadratic in the SU(n) currents are introduced, scale invariance (with anomalous dimensions) is maintained only for values of the coupling g_v=0 or $\text{g}{}_{\mathrm{<mtext>v</mtext>}}\text{=}\text{4φ}\text{(n+1)}$.