Hadronic Phases in High-Density Nuclear Matter and Neutron Stars

研究了超子混合在中子星物质基态的超离子物质中可能存在的介子凝聚。利用SU(3)xSU(3)有效手征拉格朗日量计算了P波Kaon-重子相互作用和S波相互作用。高密度物质中的重子势也通过非相对论有效重子-重子相互作用来考虑，这些相互作用是基于超核实验的最新信息。(1)得到了K介子的色散关系。结果表明，由p波Kaon-重子相互作用产生的具有K^+和K^-量子数的集体粒子-空穴模对的产生是不稳定的。这种不稳定性的起始密度比S波K^凝聚的起始密度低。(2)研究了Kaon凝聚相的状态方程，讨论了状态方程对中子星静态性质的影响。结果表明，在充分发展阶段，p波相互作用的影响很小，当密度较高时，K介子凝聚变为S波型。由于S波介子-重子相互作用，状态方程变得非常软。在麦克斯韦构造后，除了具有一级相变的介子凝聚分支外，还有一个类似于奇异星的自束束态的介子凝聚的自束缚分支。整颗恒星都是由高密度的介子凝聚体组成的。自束缚恒星包含一个亚稳区，因此它最终衰变成一颗稳定的恒星，这是通过麦克斯韦的构造和总重子数固定获得的。在半经典近似下估算了介子凝聚自束缚星的寿命。它的寿命有可能比宇宙的年龄更长，因此这颗自我束缚的恒星实质上是稳定的。

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.