Bethe Ansatz and Thermodynamic Limit of Affine Quantum Group Invariant   Extensions of the t-J Model
  We have constructed a one dimensional exactly solvable model, which is based on the t-J model of strongly correlated electrons, but which has additional quantum group symmetry, ensuring the degeneration of states. We use Bethe Ansatz technique to investigate this model. The thermodynamic limit of the model is considered and equations for different density functions written down. These equations demonstrate that the additional colour degrees of freedom of the model behave as in a gauge theory, namely an arbitrary distribution of colour indices over particles leave invariant the energy of the ground state and the excitations. The $S$-matrix of the model is shown to be the product of the ordinary $t-J$ model $S$-matrix and the unity matrix in the colour space. 
J.Ambjorn, A.Avakyan, T.Hakobyan and A. Sedrakyan