The WZNW Model As An Integrable Perturbation Of The Witten Conformal Point

We show that the WZNW model with arbitrary σ-model coupling constant may be viewed as a σ-model perturbation of the WZNW theory around the Witten conformal point. In order for the σ-model perturbation to be relevant, the level k of the underlying affine algebra has to be negative. We prove that in the large |k| limit the perturbed WZNW system with negative k flows to the conformal WZNW model with positive level. The flow appears to be integrable due to the existence of conserved currents satisfying the Lax equation. This fact is in a favorable agreement with the integrability of the WZNW model discovered by Polyakov and Wiegmann within the Bethe ansatz technique.