  The density of states and the optical conductivity of the doped Hubbard model
on a Bethe lattice with infinite connectivities have been studied using an
analytic variant of the Lanczos continued fraction method. The spectral weight
of the gap states and the position of the chemical potential upon hole or
electron doping have been studied. We argue that the strong correlation effects
such as gap states and midinfrared band shown in two dimensions also appear in
infinite dimensions.
