  We have investigated the three-body force (TBF) effect on the neutron and
proton momentum distributions in asymmetric nuclear matter within the framework
of the extended Brueckner-Hartree-Fock approach by adopting the $AV18$ two-body
interaction plus a microscopic TBF. In asymmetric nuclear matter, it is shown
that the neutron and proton momentum distributions become different from their
common distribution in symmetric nuclear matter. The predicted depletion of the
proton hole states increases while the neutron one decreases as a function of
isospin-asymmetry. The TBF effect on the neutron and proton momentum
distributions turns out to be negligibly weak at low densities around and below
the normal nuclear density. The TBF effect is found to become sizable only at
high densities well above the saturation density, and inclusion of the TBF
leads to an overall enhancement of the depletion of the neutron and proton
Fermi seas.
