Takumi Muto

Equation of state with kaon condensates and neutron stars

Abstract Kaon condensation in dense neutron star matter is investigated on the basis of current algebra and PCAC (partially conserved axial-vector current). Second-order perturbation effects are incorporated naturally within framework, which are necessary to be consistent with KN scattering data, but we find it hardly affects K − condensation. The excitation energy of kaons in a nuclear medium is examined by combining the framework with a relativistic mean-field theory. Next we obtain the equation of state of the K − -condensed phase in neutron star matter, and clarify characteristic features of the system. There can occur a first-order phase transition from the normal phase to the K − -condensed one. Subsequently bulk structure of kaon-condensed neutron stars is studied. Softening of the equation of state due to kaon condensation has a large influence on the internal structure of the neutron star. As a dynamical property associated with the first-order phase transition, the energy release due to a collapse from a metastable configuration to a stable kaon-condensed one is estimated. Its implications for the gamma-ray bursts are briefly mentioned.

Kaon condensation and equation of state in the relativistic mean-field theory

Abstract The equation of state of the kaon-condensed phase is studied within a relativistic formalism. We find a self-suppression mechanism such that the kaon condensate decreases the nucleon effective mass through the relativistic effect, which reduces the interaction energy between the nucleon and kaon in a high density region, suppressing the development of the condensate. To get more insight into this feature we extend a chiral symmetry approach and incorporate the relativistic mean field theory. In this extended treatment the σ mean-field enhances the self-suppression mechanism. Some features of kaon-condensed neutron stars are briefly discussed.

A Chiral Symmetry Approach to Meson Condensations

Various types of meson condensations are discussed within the chiral symmetry approach. For P-wave pion condensations, some realistic effects such as inclusion of the isobar .d(l232), baryon-baryon short range correlations, and form factors are taken into account in a simple way; inclusion of isobar is described in terms of SU(4) constituent quark model and short range correlations are simulated by the minimal interactions with the Landau-Migdal parameter. Kaon condensation by virtue of s-wave condensation is also described in a similar framework.

Extra Neutrino Emissivity of Neutron Stars under the Combined Condensation of Neutral and Charged Pions

Extra neutrino emissivity of neutron stars under the combined condensation of neutral and charged pions (CPC), which we call quasi-particle URCA process, is examined in a realistic approach. Here the isobar L1 (1232) degrees of freedom, baryon-baryon short-range correlations and p-wave form factors are considered consistently in the 7r-baryon and weak interaction vertices. Each role of neutral and charged pion condensate played in this process is clarified and a peculiar role of neutral pion condensate is emphasized. Our results show that quasi-particle URCA process is still dominant over other standard processes, e.g., the modified URCA process, while the emissivity is about one order of magnitude less than the one for the pure charged pion condensed case within a realistic approach.