PERTURBATION-THEORY OF LOW-DIMENSIONAL QUANTUM LIQUIDS .2. OPERATOR DESCRIPTION OF VIRASORO ALGEBRAS IN INTEGRABLE SYSTEMS

We show that the recently developed pseudoparticle-operator algebra wh ich generates the low-energy Hamiltonian eigenstates of multicomponent integrable systems with contact interactions also provides a natural operator representation for the Virasoro algebras associated with the conformal-invariant character of the low-energy spectrum of these mode ls. Studying explicitly the Hubbard chain in a nonzero chemical potent ial and external magnetic field, we establish that the pseudoparticle- perturbation theory provides a correct starting point for the construc tion of a suitable critical-point Hamiltonian. We derive explicit expr essions in terms of pseudoparticle operators for the generators of the Virasoro algebras and the energy-momentum tensor, describe the confor mal-invariant character of the critical point from the point of view o f the response to curvature of the two-dimensional space time, and dis cuss the relation to Kac-Moody algebras and dynamical separation.