Baryon Superfluidity and Neutrino Cooling of Neutron Stars

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Baryon superfluidity and neutrino emissibity are investigated for normal and hyperon-mixed neutron stars and the physical inputs necessary for neutron star cooling calculations are presented. By perfuming the cooling calculations, it is found that the so-called "hyperon cooling" (hyperon direct URCA process) combined with hyperon superfluidity is a promising candidate for a fast nonstandard cooling scenario responsible for some neutron stars which are too cold to be explained by the standard cooling, namely, the modified URCA process.However this hyperon cooling breaks down due to the disappearance of Λ-superfluidity; if a less attractive ΛΛ interaction suggested recently by the "NAGARA event" (_<Λ^^6Λ>He) becomes definite. In this context, a possibility of Λ-superfluid due to the ΛΣ^-pairing instead of ΛΛ one is discussed by formulating the BCS theory for the case with different Fermi surfaces.As another fast cooling scenario, "pion cooling" is also investigated. The superfluid energy gap of quasibaryons under the combined pion condensation with Δ-Isobar effects is calculated by extending the BCS formalism to the quasibaryon pairing and constructing the pair state to utilize most efficiently the ^3P_2 attraction. The energy gap of (0.1〜1) MeV is found, which means that only the pion cooling can be a fast cooling scenario compatible with observations when the hyperon cooling does not hold.