Probing the nuclear equation of state using the neutron star observables within the Bayesian inference approach

The constraint on nuclear matter's equation of state has been a shared goal in nuclear physics and astrophysics. The most difficult one to constrain the equation of state is the constraint on the symmetry energy in nuclear matter. In this study, we adopt a theoretical framework that combines an isospin-dependent parametric equation of state for neutron star cores with a Bayesian inference approach to calculate the posterior probability distribution functions of the parameters of the equation of state in the nuclear matter based on mass and radius data reported by the LIGO/Virgo and NICER Collaborations, and thus constrain both the equation of state in symmetric nuclear matter and the equation of state in non-symmetric nuclear matter. It is found that a stiffer equation of state is supported by the data from the NICER Collaboration, and the improvement in the equation of state is not observed. The 68% credible intervals for the parameters are L = 45(-9)(+15) MeV for the slope, K-sym = -100(-110)(+50) MeV for the curvature parameters of the symmetry energy and J(0) = -180(-40)(+60) MeV for the skewness parameter of the equation of state of symmetric nuclear matter. The symmetry energy values at two and three times normal density are, respectively, E-sym (2 rho(0)) = 48.9(-16)(+7.8) MeV and E-sym(3 rho(0)) = 81.8(-57.2)(+21.1) MeV.