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We addressed possible ambiguities on the properties of neutron stars (NSs) estimated in theoretical sides. First, roles of hyperons inside the NS are discussed through various relativistic mean field (RMF) theories. In particular, the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry is shown to give rise to the increase of hyperon threshold density, similarly to the Fock term effects in RMF theories. As a result, about 2.0 solar mass is obtained with the hyperons. Second, the effect by the modified f(R) gravity, which leaves a room for the dark energy in the Einstein equation to be taken into account, is discussed for the NS in a strong magnetic field (MF). Our results show that the modified gravity with the Kaluza-Klein electro-magnetism theory expanded in terms of a length scale parameter may reasonably describe the NS in strong MF, so called magnetar. Even the super-soft equation of state is shown to be revived by the modified f(R) gravity. [ABSTRACT FROM AUTHOR]

We calculate the neutrino scattering and absorption on the hot and dense neutron-star matter with hyperons under the strong magnetic field using perturbative approach. We find that the absorption cross-sections show the remarkable angular dependence: its strength is reduced in the direction parallel to the magnetic field and enhanced in the opposite direction. This variation becomes about 2.2% when the magnetic field is about 2×1017 G. [ABSTRACT FROM AUTHOR]