Traditional models of nuclear forces require a short range
repulsion in order to fit nucleon-nucleon scattering observables.
However, if the assumption of locality (dependence on coordinates
and not on momenta) is relaxed, as is suggested by the underlying
quark structure, the short range correlations can be quite different.

Models with a non-local short range attraction were already suggested
by Neudatchin and Kukulin more than 30 years ago. However, more recently,
evidence has developed from several nuclear reactions which also points
in this direction.

To illustrate the physics, I will discuss some models of nuclear saturation
which use simplified model interactions between nucleons.
One key conclusion is that nucleon-nucleon scattering phase shifts
alone are not sufficient to determine the nuclear equation of state.
Short range correlations also play a key role.