  The one-electron spectral function of the Holstein-Hubbard bipolaron in one
dimension is studied using cluster perturbation theory together with the
Lanczos method. In contrast to other approaches, this allows one to calculate
the spectrum at continuous wave vectors and thereby to study, for the first
time, the dispersion and the spectral weight of quasiparticle features. The
formation of polarons and bipolarons, and their manifestation in the spectral
properties of the system, is studied for the cases of intermediate and large
phonon frequencies, with and without Coulomb interaction. A good agreement is
found with the most accurate calculations of the bipolaron dispersion
available, over a large range of the electron-phonon coupling strength.
Additionally, pronounced deviations of the bipolaron dispersion from a simple
tight-binding band are found, which can be attributed to next-nearest-neighbor
hopping processes.
