We analyze the coset model (E c 2 × E c 2)/E c 2 and construct a class of exact string vacua which describe plane gravitational waves and their duals, generalizing the plane wave background found by Nappi and Witten. In particular, the vector gauging describes a two-parameter family of singular geometries with two isometries, which is dual to plane gravitational waves. In addition, there is a m...

We consider gauged WZWmodels based on a four dimensional non-semi-simple group. We obtain conformal σ-models in D = 3 spacetime dimensions (with exact central charge c = 3) by axially and vectorially gauging a one-dimensional subgroup. The model obtained in the axial gauging is related to the 3D black string after a correlated limit is taken in the latter model. By identifying the CFT correspon...