YANG-BAXTER SYMMETRY IN INTEGRABLE MODELS - NEW LIGHT FROM THE BETHE-ANSATZ SOLUTION

We show how any integrable 2D QFT enjoys the existence of infinitely m any non-abelian conserved charges satisfying a Yang-Baxter symmetry al gebra. These charges are generated by quantum monodromy operators and provide a representation of q-deformed affine Lie algebras. We review and generalize the work of de Vega, Eichenherr and Maillet on the boot strap construction of the quantum monodromy operators to the sine-Gord on (or massive Thirring) model, where such operators do not possess a classical analogue. Within the light-cone approach to the mT model, we explicitly compute the eigenvalues of the six-vertex alternating tran sfer matrix tau(lambda) on a generic physical state, through the algeb raic Bethe ansatz. In the thermodynamic limit tau(lambda) turns out to be a two-valued periodic function. One determination generates the lo cal abelian charges, including energy and momentum, while the other yi elds the abelian subalgebra of the (non-local) YB algebra. In particul ar, the bootstrap results coincide with the ratio between the two dete rminations of the lattice transfer matrix.