Hyperon Superfluidity in Neutron Star Cores

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The "hyperon cooling" can be a promising candidate for a rapid cooling scenario demanded for some neutron stars with low surface temperature, if superfluidity of hyperons admixed in neutron star cores is realized. The aim of this research project is to study whether hyperon superfluids can be possible or not. So far (2001〜2002), (1) we clarified the mechanism for the occurence of hyperon mixing and proposed a realistic neutron star model with a hyperon-mixed core, and (2) determined the superfluid density-regions for respective baryon components (n, p, Λ, Σ^-), on the basis of the results for (1) and (2). The results newly obtained in 2003 are as follows.1. We have obtained ν-emissibities for various ν-emission processes (modified URCA, Cooper-pair, nucleon direct-URCA, hyperon direct-URCA) and clarified what is most effective according to the density ρ. Thus we have provided the basic physical inputs for neutron star cooling calculations and pointed out that the nucleon direct-URCA process is forbidden and the cooper-pair process dominates in the ^3P_2 n-superfluidity.2. We have shown that the Λ-superfluidity disappears and hence the "hyperon cooling" scenario breaks down, if "less attractive ΛΛ interaction" suggested very recently by ^6_<ΛΛ>He, a so-called "NAGARA event" is true. A revival of Λ-superfluid due to ΛΣ^-pairing (instead of ΛΛ one), if possible, is a way to overcome the problem and is our forthcoming subject.