Finite-frequency optical absorption in 1D conductors and Mott-Hubbard   insulators
  The frequency-dependent conductivity is studied for the one-dimensional Hubbard model, using a selection rule, the Bethe ansatz, and symmetries associated with conservation laws. For densities where the system is metallic the absorption spectrum has two contributions, a Drude peak at $\omega = 0$ separated by a pseudogap from a broad absorption band whose lower edge is characterized by a non-classical critical exponent. Our findings shed new light on the ``far infrared puzzle'' and other optical properties of metallic organic chain compounds. 
J.M.P. Carmelo and N. M. R. Peres (Univ. of Evora), P. D. Sacramento   (CFIF, Inst. Sup. Tecnico)