  The applicability of the Hartree-Fock and random phase approximations to
models of strongly correlated electrons is discussed. The 2D Hubbard model is
analyzed. An antiferromagnetic phase (at half filling) and Fermi liquid
behavior (at low electron densities) are found. In addition, the system shows
an unconventional regime near half filling. It is characterized by the
formation of spin and charge textures. Local magnetic moments and spin waves
are also present, and the quasiparticle pole at the Fermi energy vanishes. The
charge excitation spectrum is gapless. The overall features resemble those of
the 1D Luttinger liquid.
