  The two-dimensional two-orbital Hubbard model is studied with the use of
finite-size cluster worldline quantum Monte Carlo algorithm. This model is
widely used for simulation of the band structure of FeAs clusters, which are
structure elements of Fe-based high-temperature superconductors. The choice of
a special basis set of hyper-sites allowed to take into account four-fermion
operator terms and to overcome partly the sign problem. Spectral functions and
the density of states for various parameters of the model are obtained in the
undoped and low-doped regimes. The correlated distortion of the spectral
density with the change of doping is observed, and the applicability of the
"hard-band" approximation in the doped regime is demonstrated. Profiles of the
momentum distribution are obtained for the first Brillouin zone; they have
pronounced jump near the Fermi level, which decreases with the growth of the
strength of the interaction. The invariance of the Fermi surface with respect
to the strength of the interaction is testified. Nesting is found in the case
of electron and hole doping. Fermi-liquid parameters of the model are derived.
Z-factor grows sharply with the increasing the level of doping, and
monotonously decreases with the growth of the strength of the interaction.
Moreover, electron-hole doping asymmetry of the Z-factor is revealed. The
non-Fermi liquid behaviour and the deviation from Luttinger theorem are
observed.
