  The relation between nuclear saturation and NN-correlations is examined.
Nucleons bound in a nucleus have a reduced effective mass due to the mean
field. This results in off-energy-shell scatterings modifying the free-space
NN-interaction by a dispersion correction. This is a major contribution to the
density-dependence of the effective in-medium force and to saturation.
Low-momentum effective interactions have been derived by renormalisation
methods whereby correlations may be reduced by effectively cutting off high
momentum components of the interaction. The effect of these cut-offs on
dispersive corrections and on saturation is the main focus of this paper. The
role of the tensor-force, its strength and its effect on correlations is of
particular interest. The importance of the definition of the mean field in
determining saturation as well as compressibility is also pointed out.
  With a cut-off below $\sim 2.6 fm^{-1}$ there is no saturation but at lower
density the binding energy is still well approximated suggesting that such a
force may be useful in nuclear structure calculations of (small) finite nuclei
if saturation is not an issue.
  A separable interaction that fits experimental phase-shifts exactly by
inverse scattering methods is used. Recent experiments measure short ranged
correlations (SRC's) to be 0.23 for $^{56}Fe$. Other experiments have obtained
a depletion of occupation-numbers in $^{208}Pb$ to be $\sim 0.2$. For nuclear
matter with the separable interaction and a continuous spectrum we obtain the
related quantity $\kappa$ to be 0.175 with the Bonn-B deuteron parameters,
while Machleidt's gets $\kappa= 0.125$ for the Bonn-B potential and a
continuous spectrum.
