  We introduce the pseudohole and heavy-pseudoparticle operator algebra that
generates all Hubbard-chain eigenstates from a single reference vacuum. In
addition to the pseudoholes already introduced for the description of the
low-energy physics, this involves the heavy pseudoparticles associated with
Hamiltonian eigenstates whose energy spectrum has a gap relatively to the
many-electron ground state. We introduce a generalized pseudoparticle
perturbation theory which describes the relevant finite-energy ground state
transitions. In the present basis these excitations refer to a small density of
excited pseudoparticles. Our operator basis goes beyond the Bethe-ansatz
solution and it is the suitable and correct starting point for the study of the
finite-frequency properties, which are of great relevance for the understanding
of the unusual spectral properties detected in low-dimensional novel materials.
