Saturation in the Nuclear Matter Problem
  Once density-dependent meson masses are introduced into the nuclear many-body problem, conventional mechanisms for saturation no longer operate. We suggest that a loop correction, essentially the introduction of the axial vector coupling $g_A(\rho,k)$ as function of density $\rho$ and momentum $k$, can bring about saturation, and present schematic calculations to illustrate this. We find that a very small density-dependence in $g_A$ gives rise to a very large saturating effect on nuclear matter. In fact, this new saturation mechanism turns out to be more powerful than any of the conventional mechanisms. 
G. E. Brown and R. Machleidt