  Predictions are made for the momentum- and carrier-dependent degradation of
the Mott gap upon doping in high-Tc cuprates as would be observed in Cu K-edge
resonant inelastic x-ray scattering (RIXS). The two-dimensional Hubbard model
with second- and third-nearest-neighbor hopping terms has been studied by
numerical exact diagonalization. Special emphasis is placed on the
particle-hole asymmetry of the Mott gap excitations. We argue that the Mott gap
excitations observed by RIXS are significantly influenced by the interaction
between charge carriers and antiferromagnetic correlations.
