Positive and Negative Hierarchies of Integrable Lattice Models Associated with a Hamiltonian Pair

Abstract

A difference Hamiltonian operator involving two arbitrary constants is presented, and it is used to construct a pair of nondegenerate Hamiltonian operators. The resulting Hamiltonian pair yields two difference hereditary operators, and the associated positive and negative hierarchies of nonlinear integrable lattice models are derived through the bi-Hamiltonian formulation. Moreover, the two lattice hierarchies are proved to have discrete zero curvature representations associated with a discrete spectral problem, which also shows that the positive and negative hierarchies correspond to positive and negative power expansions of Lax operators with respect to the spectral parameter, respectively. The use of zero curvature equation leads us to conclude that all resulting integrable lattice models are local and that the integrable lattice models in the positive hierarchy are of polynomial type and the integrable lattice models in the negative hierarchy are of rational type.