Nuclear-matter incompressibility from fits of generalized Skyrme force to breathing-mode energies

In an attempt to extend the range of values of K-v, the incompressibility of symmetric nuclear matter, for which fits to the measured breathing-mode energies are possible, we investigate generalized Skyrme-type forces with a term that is both density- and momentum-dependent. Acceptable fits are found to be possible only for values of K-v in the range 215 +/- 15 MeV. For higher values fits are impossible, while for lower values fits are achieved only by introducing an unphysical collapse of nuclear matter. Thus our generalization of the Skyrme force does not permit a significantly wider range of values of K-v than that already given by force SkM*. However, with a view to having a more reliable estimate of the compressional properties of the highly neutron-rich nuclear matter that comprises the core of collapsed stars, we present a new version of this latter force giving a much better fit to the masses of neutron-rich nuclei. Comparison with force SkM* also shows that the value of K-v extracted from the breathing-mode energies is essentially independent of the choice of effective mass. By providing a counter-example, we show that K-v cannot be extracted from masses and charge distributions alone. As for the third-order coefficient K', we cannot be more precise than to say that it lies in the interval 700 +/- 500 MeV. (C) 1997 Elsevier Science B.V.