  We consider the 2D Hubbard model in the strong-coupling case (U>>W) and at
low electron density (nd^2<<1). We find an antibound state as a pole in the
two-particle T-matrix. The contribution of this pole in the self-energy
reproduces a two-pole structure in the dressed one-particle Green-function
similar to the Hubbard-I approximation. We also discuss briefly the
Engelbrecht-Randeria mode which corresponds to the pairing of two holes below
the bottom of the band for U>>W and low electron density. Both poles produce
non-trivial corrections to Landau Fermi-liquid picture already at low electron
density but do not destroy it in 2D

Strongly Correlated Electrons;Superconductivity