Renormalization and conformal properties of σ models on Riemannian space with torsion

The conformal properties of two-dimensional σ models, whose target space is a Riemann manifold with torsion, are investigated. A general procedure for dealing with the peculiar infrared behavior of the scalar massless field in two dimensions is proposed. By means of this procedure, the renormalized energy-momentum tensor and tachyon vertex operator are explicitly constructed in perturbation theory. It is shown that the freedom arising in the process of renormalization is fixed imposing the conformal Ward identities