Hadronic Phases in High-Density Nuclear Matter and Neutron Stars

在超子物质中，超子混合在中子星物质的基态，研究了超子凝聚存在的可能性。利用SU(3) xSU(3)有效手性拉格朗日量，包括了p波的介子-重子相互作用以及s波的相互作用。高密度物质中的重子势也通过非相对论性的有效重子-重子相互作用来考虑，这些相互作用是基于最近的超核实验的信息。(1)得到了介子的色散关系。研究表明，由于p波介子-重子相互作用，产生具有K^+和K^-量子数的集体粒子-空穴模式对时，存在不稳定性。这种不稳定性的起始密度低于s波K^-凝聚的起始密度。(2)研究了介子凝聚相的态方程，讨论了态方程对中子星静态特性的影响。结果表明，在完全发育阶段，p波相互作用的影响很小，在较高的密度下，k介子凝聚成为s波型。由于s波的介子-重子相互作用，EOS变得非常软。除了麦克斯韦构造后具有一阶相变的介子凝聚分支外，还有一个介子凝聚的“自束缚”分支，就像一颗奇异恒星的自束缚态一样。整个恒星由高密度的介子凝聚体组成。自束缚恒星包含一个亚稳区，因此它最终衰变成一个固定重子总数的麦克斯韦构造得到的稳定恒星。在半经典近似中估计了介子凝聚自束缚星的寿命。有可能它的寿命比宇宙的年龄还要长，所以这颗自我束缚的恒星基本上是稳定的。

Possible existence of kaon condensation in hyperonic matter, where hyperons are mixed in the ground state of neutron-star matter, has been investigated. P-wave kaon-baryon interactions are included as well as s-wave ones by the use of the SU(3) xSU(3) effective chiral Lagrangian. Baryonic potentials in high-density matter are also taken into account through the nonrelativistic effective baryon-baryon interactions which are based on the recent information from hypernuclear experiments. (1) The dispersion relations of kaons have been obtained. It has been shown that there appears an instability with respect to a pair creation of collective particle-hole modes with K^+ and K^-quantum numbers, stemming from the p-wave kaon-baryon interaction. The onset density of this instability is lower than that of the s-wave K^-condensation. (2) The equation of state (EOS) of the kaon-condensed phase has been studied, and the effects of the EOS on the static properties of neutron stars have been discussed. It has been shown that in the fully-developed phase, the effects of p-wave interactions are small, and that kaon condensation becomes of the s-wave type at higher density. The EOS becomes very soft owing to the s-wave kaon-baryon interactions. In addition to the kaon-condensed branch with a first-order phase transition after Maxwell's construction, there is a kaon-condensed 'self-bound' branch just like a self-bound state for a strange star. The whole star is composed of kaon condensates with high-density. The self-bound star contains a metastable region, so that it eventually decays into a stable star obtained with Maxwell's construction with the total baryon number fixed. The lifetime of the kaon-condensed self-bound star has been estimated in a semi-classical approximation. It is possible that the lifetime is longer than the age of the universe, so that the self-bound star is substantially stable.