Angular quantization and form factors in massive integrable models

We discuss an application of the method of angular quantization to the reconstruction of form factors of local fields in massive integrable models, The general formalism is illustrated with examples of the Klein-Gordon, sinh-Gordon and Bullough-Dodd models. For the fatter two models the angular quantization approach makes it possible to obtain free field representations for form factors of exponential operators. We discuss an intriguing relation between the free field representations and deformations of the Virasoro algebra. The deformation associated with the Bullough-Dodd models appears to be different from the known deformed Virasoro algebra. (C) 1998 Elsevier Science B.V.