Kaon condensation in hyperonic matter and properties of neutron stars

The equation of state (EOS) of kaon condensation in hyperonic matter, where hyperons (Λ,Σ−) are mixed in the ground state of neutron-star matter, is investigated. P-wave kaon-baryon interactions are included as well as s-wave ones by the use of effective chiral Lagrangian. It is shown that kaon condensates appear with finite momentum, stemming from the attractive p-wave kaon-baryon interactions. However, in the fully-developed phase, the s-wave kaon-baryon interactions control the EOS, and kaon condensation becomes of an s-wave type at higher density. Due to a considerable softening of the EOS caused by both hyperon-mixing and kaon condensates, the energy of the system has a local minimum, which leads to a metastable configuration of self-bound kaon-condensed star in addition to a usual kaon-condensed star obtained by Maxwell's construction.