Neutron star is one of final products of stellar evolution. The major ingredient of neutron star is believed to be neutrons but hyperons can also exist in the central area of the neutron star. We calculate theoretically the radius and mass of neutron stars using various models describing nuclear matter. Most models including hyperons predict maximum mass of the neutron star lower than the observed maximum mass, 2.01±0.04 M⊙ of PSR J0348+0432. This contradiction is called the hyperon puzzle. Two equations are needed in order to calculate the radius and mass of the neutron star. One is the Tolman-Oppenheimer-Volkoff (TOV) equation coming from the Einstein field equation. The other is the equation of state (EoS) which is a relation between energy density and pressure. EoS can be obtained from various models which describe nuclear matter. In this thesis, we choose a relativistic mean field (RMF) model to determine the EoS. The RMF model, which is a phenomenological model, is an effective field model where the interaction between baryons in the matter is described by exchanges of mesons. We compare the calculated maximum mass of the neutron star depending on the existence of hyperons as well as neutron, proton and leptons. Furthermore, we suggest a way to treat the hyperon puzzle by introducing the φ meson and varying coupling constants.
Thesis Advisor: Prof. Yongseok Oh