Study of New Phases in High Density Strange Matter

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In this project, new phases with large strangeness have been studied from various viewpoints, and we have obtained the main results as descibed below.1. Saturation property of strange quark matter (abbreviated to SQM) : In order to clarify the reality of E.Witten's conjecture on the possibility that SQM is the true hadronic ground state, studies with use of two QCD-motivated effective models (constituent quark model and bag model) have been done. The results by treating both finite and infinite systems unifiedly have shown the increase of energy per baryon E/A beyond the s-closed shell(A>6). This means that the existence of absolutely stable SQM is unlikely as far as the fundamental parameters built in such effective theories do not change substantially with incease of A.2. Kaon condensation : Realization mechanism of this phase has been studied in chiral symmetry approach. We have shown the remarkable increase of proton mixing with growth of K^- condensation and the possible occurrence of the direct URCA process for the symmetry energy with reasonable density dependence, and the resulting rapid cooling of neutron stars due to this process.3. Effects of hadoronic condensed phases with and without strangeness to supernovae matter and neutron star matter : Properties of condensed phases in supernovae matter just after birth of neutron stars and thermal and dynamical evolution have been studied. We have made clear that meson condensates and symmetry energy are strongly relevant to the whole processes from the birth to the well-cooled stage of neutron stars.4. Nuclear force in the systems with strangeness : Study of baryon structure and hyperon-nucleon interaction has progressed in the quark-cluster model by taking account of the breaking of the flavor SU(3) symmetry. This provides a base to study the interaction between H-particles which is indispensable for study of H-matter(strange matter with partial deconfinement).