On the geometry of the parameter space in two-dimensional generalized U(N) Thirring models

We extend the study of two-dimensional generalized U(N) Thirring models to the third perturbative order, by the computation of the β functions and of the leading order in 1/N of the metric Gij; we derive the existence of a non-trivial Riemann tensor in the parameter space and the rotationality of the covariant βi vector, which disproves a series of conjectures. (orig.)