对核物质状态方程基于中子星观测的贝叶斯统计研究

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

核物质状态方程的确定是核物理和天体物理所共有的核心科学目标之一,其不确定性主要源于核物质对称能的不确定.本文采用同位旋相关的参数化状态方程模型与贝叶斯统计方法相结合的理论框架,基于LIGO/Virgo合作组和NICER合作组发布的中子星质量和半径的观测数据计算描述核物质状态方程参数的后验概率分布,约束对称核物质状态方程和核物质对称能.研究发现,NICER合作组发布的中子星观测数据支持较硬的核物质状态方程,并且相比之前核物质状态方程的约束结果,NICER最新的数据没有改善人们对核物质对称能的认识.最新的关于状态方程参数的68%的置信区间为对称能斜率参数L=45_(−9)^(+15)L=45−9+15 MeV,对称能曲率参数K_(sym)=−100_(−110)^(+50)MeV,而对称核物质偏度参数J_(0)=−180_(−40)^(+60)MeV.两倍和三倍饱和密度处对称能的68%的置信范围分别为E_(sym)(2ρ0)=48.9_(-16)^(+7.8)MeV和E_(sym)(3ρ0)=81.8_(−57.2)^(+21.1)MeV.

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)(2ρ0)=48.9_(-16)^(+7.8)MeV and E_(sym)(3ρ0)=81.8_(-57.2)^(+21.1)MeV.