Colours associated to nonsimply-laced Lie algebras and exact S-matrices

A new set of exact scattering matrices in 1 + 1 dimensions is proposed by s olving the bootstrap equations. Extending earlier constructions of colour v alued scattering matrices this new set has its colour structure associated to nonsimply-laced Lie algebras, This in particular leads to a coupling of different affine Toda models whose fusing structure has to be matched in a suitable manner. The definition of the new S-matrices is motivated by the s emiclassical particle spectrum of the nonsimply-laced Homogeneous Sine-Gord on (HSG) models, which are integrable perturbations of WZNW cosets. In part icular, the S-matrices of the simply-laced HSG models are recovered as a sp ecial case. (C) 2001 Published by Elsevier Science B.V.