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arXiv 2104.02514nucl-thastro-ph.HE
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相对论性点耦合模型中的原子核面和对称能

Nuclear pasta and symmetry energy in the relativistic point-coupling model

Fan Ji, Jinniu Hu, Hong Shen

摘要:

低密度核物质的不均匀结构,被称为核面食,预计不仅会出现在中子星的内壳中,而且还会出现在核心坍缩的超新星爆炸和中子星合并中。我们利用费密近似对低密度区的非均匀核物质和中子星物质进行了全三维计算。核相互作用用相对论平均场方法描述,用点耦合相互作用代替每个通道中的介子交换作用。通过在等尺度矢量相互作用和等矢量矢量相互作用之间引入耦合项,我们研究了核对称能及其密度依赖性对pasta结构的影响。研究发现,丰中子物质中的pasta相的性质强烈依赖于对称能及其斜率。除了典型的形状,如液滴,棒,板,管和气泡,一些中间面食结构也观察到在冷恒星物质与相对较大的质子分数。我们发现,非球形的形状是不可能形成的中子星壳,因为质子分数在$β$平衡是相当小的。内壳的性质可能导致中子星半径的明显差异。

英文摘要:

Nonuniform structure of low-density nuclear matter, known as nuclear pasta, is expected to appear not only in the inner crust of neutron stars but also in core-collapse supernova explosions and neutron-star mergers. We perform fully three-dimensional calculations of inhomogeneous nuclear matter and neutron-star matter in the low-density region using the Thomas-Fermi approximation. The nuclear interaction is described in the relativistic mean-field approach with the point-coupling interaction, where the meson exchange in each channel is replaced by the contact interaction between nucleons. We investigate the influence of nuclear symmetry energy and its density dependence on pasta structures by introducing a coupling term between the isoscalar-vector and isovector-vector interactions. It is found that the properties of pasta phases in the neutron-rich matter are strongly dependent on the symmetry energy and its slope. In addition to typical shapes like droplets, rods, slabs, tubes, and bubbles, some intermediate pasta structures are also observed in cold stellar matter with a relatively large proton fraction. We find that nonspherical shapes are unlikely to be formed in neutron-star crusts, since the proton fraction obtained in $β$ equilibrium is rather small. The inner crust properties may lead to a visible difference in the neutron-star radius.

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