  Widths of low-lying states in nuclei are of the order of 30 MeV. These large
widths are a consequence of the strong interactions leading to a strongly
correlated many body system at the typical densities of nuclear matter.
Nevertheless "traditional" Brueckner calculations treat these states as
quasiparticles i.e. with spectral functions of zero widths. The width is
related to the imaginary part of the selfenergy and is included
selfconsistently in an extension of the Brueckner theory using T-matrix and
Green's function techniques. A more general formulation applicable also to
non-equilibrium systems is contained in the Kadanoff-Baym (KB) equations while
still maintaining the basic many-body techniques of Bruecknet theory. In the
present work the two-time KB-equations are time-stepped along the imaginary
time-axis to calculate the binding energy of nuclear matter as a function of
density, including the spectral widths self-consistently. These zero
temperature calculations are compared with quasi-particle calculations. The
inclusion of the self-consistent widths are found to add several MeV to the
binding. The spectral widths are due to the long-ranged correlations.
Short-ranged correlations decrease rather than increase the binding. The metod
is easily extended to non-zero temperatures where the importance of the widths
are expected to increase.
