Exact excitation spectrum of the Zsub(n+1) X Zsub(n+1) generalized Heisenberg model

We describe the excitations of the generalization of the Heisenberg anisotropic hamiltonian to Zsub(n+1) spins. We analyse the Bethe ansatz equations without assuming the existence of strings. Excited states above an antiferromagnetic ground state are described by a finite number of parameters, which verify a finite system of equations. We give the energy and momentum of the excitations. In a suitable limit we recover the spectrum of a relativistically invariant theory. (orig.)