  An effective quantum field theory of the 2D Hubbard model on a square lattice
near half-filling is presented and studied. This effective model describes
so-called nodal and antinodal fermions, and it is derived from the lattice
model using a certain partial continuum limit. It is shown that the nodal
fermions can be bosonized, which leads to spin-charge separation and a 2D
analogue of a Wess-Zumino-Witten model. A bosonization formula for the nodal
fermion field operator is obtained, and an exactly solvable model of
interacting 2D fermions is identified. Different ways of treating the antinodal
fermions are also proposed.
