We present a theoretical calculation, within a continuum electron-phonon-coupled model, of the optical absorption due to polarons in polyacetylene [{CH), ]. Our results can be applied to both transand cis-(CH)", as well as potentially to other polymers (polypyroles, polyparaphenylenes) in which polarons are present. We establish that the essential signature of polaron absorption is the existence of three separate absorption peaks in the gap with qualitatively different features. For trans-(CH)", we compare and contrast this structure with that from the kink solitons, which are expected to dominate the optical absorption at all but the lowest doping levels. For cis-(CH) and related polymers, we discuss polaron (and multipolaron) absorption and the relation of polarons to possible excitons in these materials. Finally, we evaluate briefly the existing experimental situation regarding optical absorption in polyacetylene and indicate possible future experiments that could confirm the existence of polarons in (CH)"and similar polymers.

From the discrete nonlinear Schrodinger equation describing transport on a dimer we derive and solve a closed nonlinear equation for the site-occupation probability difference. Our results, which are directly relevant to specific experiments such as neutron scattering in physically realizable dimers, exhibit a transition from "free" to "self-trapped" behavior and illustrate features expected in extended systems, including soiiton/polaron bandwidth reduction and the dependence of energy-transfer efficiency on initial conditions.

We examine and explain the Luttinger-liquid character of models solvable by the Bethe ansatz by introducing a suitable bosonic operator algebra. In the case of the Hubbard chain, this involves two bosonic algebras which apply to {\it all} values of $U$, electronic density, and magnetization. Only at zero magnetization does this lead to the usual charge - spin separation. We show that our ``pseudoparticle'' operator approach clarifies, unifies, and extends several recent results, including the existence of independent right and left equations of motion and the concept of ``pseudoparticle'' (also known as ``Bethe quasiparticle'').Comment: 12 pages, RevTeX, preprint CSI