Away from Criticality: Some Results from the S Matrix Approach
In two dimensions, conformai invariance provides a natural way to classify the universality classes for critical phenomena . It is of growing interest to extend the Conformai Field Theories (CFT) away from criticality to reach a complete understanding of the scaling region around the fixed points. Zamolodchikov  found that particular deformations of the CFT preserve the integrability of the models and the corresponding massive field theories can be described by a factorizable S-matrix. The 5-matrix of the three-state Potts model  and the S-matrix of the Ising model in a magnetic field  are the first examples of this approach. The hidden E 8 symmetry of Ising model is responsible for the rich structure of the S-matrix in the latter case. Recently, other models have been discussed: the 5-matrix of non-unitary Yang-Lee edge singularity  and the S-matrix of the thermal perturbation of the tricritical Ising model . P. Christe will discuss the latter model, expecially its hidden E 7 symmetry, in his talk .
KeywordsIsing Model Dynkin Diagram Conformal Field Theory Thermal Perturbation Coxeter Number
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