Gravitational waves from WZW models

A brief review is given of the recent solution of a non-compact CFT describing a NS-supported pp-wave background. We will first explain how to compute the three- and four-point correlators using the current algebra techniques, thereby showing that some generic features of the non-compact WZW models become very clear in this simple context. We will then present the Penrose limit as a contraction of an U(1) x SU(2)(k) WZW model, an approach that could prove useful in order to understand holography for pp-wave spacetimes. We will finally comment on the string amplitudes and on the existence of two flat space limits.