Antikaon condensation in neutron stars by a new nonlinear mean-eld model

We have investigated both the K and K0 condensations in -equilibrated neutron star (NS) matter using the relativistic mean-…eld model with the renormalized meson-baryon coupling constants. Adopting the antikaon optical potential of 120MeV, our model predicts the K condensation as the second-order phase transition inside the neutron star of maximum mass, while the deeper potential than 160MeV is ruled out. This is in contrast to the result of the density-dependent hadron …eld theory. Our model also predicts remarkable softening of the equation of state by the K0 condensation at high densities. Although this is contrasted with the result of the nonlinear Walecka model, only the K condensation can be formed in NSs. 1 Introduction There recently is a considerable interest in the antikaon condensation that might be formed in dense nuclear medium as realized in high-energy heavy-ion collisions or in NSs. The relativistic mean-…eld (RMF) theory [1] has now been widely admitted to be suitable for describing such dense hadron matter [2]. Then the antikaon condensation in NSs has been investigated [3-7] by the so-called NLWmodels that include additional nonlinear selfcoupling terms of mesons in theWalecka model. It is however noted that many parameters in the NLW model are adjusted to reproduce the properties of normal nuclear matter and …nite nuclei. Therefore the NLW model is really valid at low densities, but there are no guarantees that it is useful at high densities where the antikaon condensation is expected to appear. In this respect the models embodying explicit or implicit density-dependence are desired. One of such e¤orts has been done in Ref. [8] using the density-dependent hadron …eld (DDRH) theory. However the DDRHmodel is based on the Dirac-BruecknerHartree-Fock (DBHF) theory [9], and there are no realistic DBHF calculations of baryon matter including hyperons at present in contrast to the nonrelativistic Brueckner-HartreeFock (NRBHF) theory [10,11]. As a result the density dependence of the meson-hyperon vertices in the DDRH model cannot be well determined. Therefore the other RMF models, which exhibit density dependence but are independent of the DBHF theory, are desired. Zimanyi and Moszkowski (ZM) [12] developed This paper is the revised version of CDS ext-2004-036. Some texts and mistypes have been corrected.