  The off-shell behavior of the nucleon self-energy in isospin asymmetric
nuclear matter is investigated within the framework of relativistic
Dirac-Brueckner-Hartree-Fock approach based on projection techniques. The
dependence of the Dirac components of the self-energy on momentum as well as
energy is evaluated for symmetric as well as asymmetric nuclear matter. Special
attention is paid to the various contributions to the momentum dependence of
the real and imaginary part of the optical potential. The consequences to the
different definitions of the effective nucleon mass and particle spectral
functions are discussed.
