We examine the role of hyperons in a neutron star based on the relativistic mean field approach. For nuclear matter below 1.5 times the normal nuclear density we constrain the model parameters by using the symmetric nuclear matter properties and theoretical investigations for neutron matter in the literature. We then extend the model to higher densities by including hyperons and isoscalar vector mesons that contain strangeness degree of freedom. We confirm that the φ meson induces a Λ repulsive force and hardens the equation of state. The hardening arising from the φ meson compensates the softening from the existence of hyperons. The flavor SU(3) and spin-flavor SU(6) relations are examined as well. We found that the coupling constants fitted by neutron matter properties could yield high enough maximum mass of a neutron star and the obtained results satisfy both the mass and radius constraints. The onset of the hyperon direct Urca process in neutron stars is also investigated using our parametrization.
Bibliographical noteFunding Information:
Y. L. was supported by the National Science Foundation under Grant No. PHY1652199. C. H. L. was supported by the National Research Foundation (NRF) of Korea grant funded by the Korea government (MSIP) under Grants No. NRF-2015R1A2A2A01004238 and No. NRF-2016R1A5A1013277. Y. O. was supported by the NRF of Korea under Grants No. NRF-2015R1D1A1A01059603 and No. NRF-2016K1A3A7A09005577.
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