HEISENBERG XXZ MODEL AND QUANTUM GALILEI GROUP

The 1D Heisenberg spin model with anisotropy of the XXZ type is analysed in terms of the symmetry given by the quantum Galilei group GAMMA(q)(1). For a chain with an infinite number of sites we show that the magnon excitations and the s = 1/2, n-magnon bound states are determined by the algebra. In this case the GAMMA(q)(1) symmetry provides a description naturally compatible with the Bethe ansatz. The recurrence relations determined by GAMMA(q)(1) permit us to express the energy of the n-magnon bound states in a closed form in terms of Tchebischeff polynomials.