Colour valued scattering matrices

We describe a general construction principle which allows to add colour val ues to a coupling constant dependent scattering matrix. As a concrete reali zation of this mechanism we provide a new type of S-matrix which generalize s the one of affine Toda field theory, being related to a pair of Lie algeb ras. A characteristic feature of this S-matrix is that in general it violat es parity invariance. For particular choices of the two Lie algebras involv ed this scattering matrix coincides with the one related to the scaling mod els described by the minimal affine Toda S-matrices and for other choices w ith the one of the Homogeneous sine-Gordon models with vanishing resonance parameters. We carry out the thermodynamic Bethe ansatz and identify the co rresponding ultraviolet effective central charges. (C) 2000 Elsevier Scienc e B.V. All rights reserved.