Relation of Strangeness Nuggets to Strangeness Condensation and the Maximum Mass of Neutron Stars

The recent experimental indications of density dependence in the pion decay constant f π and ω meson mass m ⋆ ω and the discovery of S (3115) and other strange “nuggets” are providing a strong support for kaon condensation in dense hadronic matter, thereby re-kindling the interest in the issue of the critical stable mass of neutron stars. The density-dependent quantities provide increases in the vector mean fields mediated by ρ and ω-meson exchange which increase by a factor ∼ 1.56 the Weinberg-Tomozawa term in kaon-nucleon interactions which accounts for ∼ half of the binding energy of the K meson in dense matter. Furthermore lattice gauge calculations have pinned down the value of KN sigma term, ΣKN , the explicit chiral symmetry breaking in the strangeness sector. The partial rotation out of this explicit breaking provides the other ∼ half of the K binding energy. The net result is to confirm the work of Thorsson et al. that strangeness condensation takes place at u = n/n0 ≃ 3, where n0 is nuclear matter density, in neutron stars. We suggest in this article that a support for this scenario is provided by the recent experiments of Suzuki et al. who found tightly bound strangeness nuggets. The strangeness nuggets discovered in the experiments involve approximately the same ratio of nucleons to K meson as in the center region of neutron stars. But whereas the latter can be described by mean fields, in which the medium effects are substantially more attractive than in the finite system, the binding in neutron star matter should be substantially (say, ∼ 20%) greater than that in the strangeness nugget. This would strengthen the argument by Brown and Bethe that the accompanying softening in the equation of state should limit the maximum neutron star mass to Preprint submitted to Elsevier Science 7 February 2008 M NS ≃ 1.5M⊙. This low M NS ∼ 1.5M⊙ has major consequences in astrophysics, especially for the merging rate of compact stellar objects.