Constraining the Nuclear Equation of State at Subsaturation Densities

Only one-third of the nucleons in Pb-208 occupy the saturation density area. Consequently, nuclear observables related to the average properties of nuclei, such as masses or radii, constrain the equation of state not at the saturation density but rather around the so-called crossing density, localized close to the mean value of the density of nuclei: rho similar or equal to 0.11 fm(-3). This provides an explanation for the empirical fact that several equation of state quantities calculated with various functionals cross at a density significantly lower than the saturation one. The third derivative M of the energy per unit of volume at the crossing density is constrained by the giant monopole resonance measurements in an isotopic chain rather than the incompressibility at saturation density. The giant monopole resonance measurements provide M = 100 +/- 70 MeV (6% uncertainty), whose extrapolation gives K-infinity = 230 +/- 40 MeV (17% uncertainty).