  We use an exact {\it holon} and {\it spinon} Landau-liquid functional which
describes the holon - spinon interactions at all scattering orders, to study
correlation functions of integrable multicomponent many-particle problems
showing both linear and non-linear energy bands. Motivated by recent
photoemission experiments, we consider specific cases when the dominant
non-linear band terms are quadratic and apply our results to the evaluation of
the half-filling 1D Hubbard model one-particle spectral functions beyond
conformal-field theory.
