Occurrence of Hyperon Superfluidity in Neutron Star Cores

Abstract

Superfluidity of $\Lambda$ and ${\Sigma }^{-}$ admixed in neutron star (NS) cores is investigated realistically for hyperon ($Y$)-mixed NS models obtained using a $G$-matrix-based effective interaction approach. Numerical results for the equation of state (EOS) with the mixing ratios of the respective components and the hyperon energy gaps including the temperature dependence are presented. These are meant to serve as physical inputs for $Y$-cooling calculations of NSs. By paying attention to the uncertainties of the EOS and the $YY$ interactions, it is shown that both $\Lambda$ and ${\Sigma }^{-}$ are superfluid as soon as they appear although the magnitude of the critical temperature and the density region where superfluidity exists depend considerably on the $YY$ pairing potential. Considering momentum triangle condition and the occurrence of superfluidity, it is found that a so-called `` hyperon cooling\rq\rq~(neutrino-emission from direct Urca process including $Y$) combined with $Y$-superfluidity may be able to account for observations of the colder class of NSs. It is remarked that $\Lambda$-hyperons play a decisive role in the hyperon cooling scenario. Some comments are given regarding the consequences of the less attractive $\Lambda \Lambda$ interaction recently suggested by the `` NAGARA event\rq\rq~${}_{\Lambda \Lambda }^6$He.

25 pages, 12figures; final version; will appear in Prog. THeor. Phys. Vol.115, No.2

References in corpus (1)

• Cooling of Neutron Stars. Hadronic Model

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