ar X iv : c on d - m at / 9 41 10 96 v 1 2 2 N ov 1 99 4 Ground states of integrable quantum liquids

Based on a recently introduced operator algebra for the description of a class of integrable quantum liquids we define the ground states for all canonical ensembles of these systems. We consider the particular case of the Hubbard chain in a magnetic field and chemical potential. The ground states of all canonical ensembles of the model can be generated by acting onto the electron vacuum (densities n < 1) or hole vacuum (densities n > 1), suitable pseudoparticle creation operators. We also evaluate the energy gaps of the non-lowest-weight states (non-LWS's) and non-highest-weight states (non-HWS's) of the eta-spin and spin algebras relative to the corresponding ground states. For all sectors of parameter space and symmetries the exact ground state of the many-electron problem is in the pseudoparticle basis the non-interacting pseudoparticle ground state. This plays a central role in the pseudoparticle perturbation theory.