Effects of Charged-Pion Condensation on Neutron 3P2 Superfluidity

Abstract

Effects of charged-pion(1IC) condensation on neutron 3 P2 superfiuidity are investigated by taking account of realistic aspects of the 1Ic condensation realized at high density in neutron star interior. Coexistence of the two hadronic condensates is formulated as the pairing correlation in the system of quasi-neutrons described as a superposition of neutron and proton by adopting an aligned angular-momemtum coupling for the 3 P2 pairing, under the restriction of the baryonic degrees of freedom to the nucleonic one. We find a mild effect of the 1Ic condensation due to which, compared with the case without the 1Ic condensation, the critical temperature of 3 P2 superfiuidity is slightly larger at densities up to about three times the nuclear density, and becomes smaller as density goes higher. Discussion is given concerning the dependence of the results on the 1Ic condensation parameters, effective mass and so forth. Coexistence of hadronic condensates is an interesting subject not only from the viewpoint of quantum many-body theory but also in neutron star problems. Recently much interest has been aroused concerning the baryonic 3 P2 superfiuidity at high density in neutron star interior in connection with neutron star cooling. To be compatible with the observed surface temperatures of neutron stars such as Vela cooled faster than the standard scenario (Le., modified URCA process), some more efficient cooling mechanism than the standard one is expected to operate. This implies the existence of some nonstandard components (including the so-called exotic ones) at high densities. 1) At the same time the role of superfiuidity is needed to suppress too rapid cooling by a nonstandard mechanism. The latter point has attracted considerable attention since 1990, in connection with the cooling due to meson condensations. 2) In order for this suppression to be operative, the energy gap should be much larger than the internal temperature l1n c::::: 10 8 K, ranging to the innermost part of neutron stars, where p ;(;3po (po being the nuclear density taken as 0.17fm- 3 ). A theoretical problem to be solved is whether the baryonic superfiuidity in the nuclear matter involving nonstandard components is possible or not. In around 1980 the present authors studied such coexistence problem of whether the nucleon superfiuidity can persist under pion condensation. 3) The model for pion condensation adopted there was the simplest one, where only the 11 - N P wave interaction is considered and the isobar degrees of freedom are not taken into account. In these studies, a positive answer was obtained; nucleon superfiuidity can coexist