  The approximation for the NJL gap equation that was developed in our previous
paper allows us to investigate vacuum inhomogeneities in the mean field
approach. The simplest case of a domain wall is studied thoroughly. The
Jackiw-Rebbi problem which arises in treatment of the fermions' interaction
with the domain wall is solved explicitly and the entire spectrum of bound
states is described. It is estabilished that under our assumptions no bound
states exist at the domain wall, however higher-order corrections may make them
appear. Thus existence of the quark bound states at domain walls may be a good
test for subtle features of QCD.
