Hierarchies of spin models related to Calogero–Moser models Original Research Article

The universal formulation of spin exchange models related to Calogero–Moser models implies the existence of integrable hierarchies, which have not been explored. We show the general structures and features of the spin exchange model hierarchies by taking as examples the well-known Heisenberg spin chain with the nearest neighbour interactions. The energy spectra of the second member of the hierarchy belonging to the models based on the Ar root systems (r=3,4,5) are explicitly and exactly evaluated. They show many interesting features and in particular, much higher degree of degeneracy than the original Heisenberg model, as expected from the integrability.