δ介子影响下的核物质与中子星性质

发布时间：2019-01-08 08:17

【摘要】：中子星由于其极端的物理条件,一直是核物理和天体物理学的研究热点。在关于中子星问题的研究中,寻找合适的状态方程(EOS)一直是长期的目标与中心的任务。中子星物质的状态方程很大程度上决定了中子星的质量半径关系。然而,对于高密下的状态方程仍然存在相当大的理论不确定性,不同理论模型给出的结果也存在很大的分歧。并且,最新研究表明目前许多理论模型给出的质量-半径关系都不符合天文观测,尤其是理论给出的中子星半径都普遍偏大。近几十年来,相对论平均场(RMF)理论在原子核结构、原子核反应和核天体物理等领域取得了很大的成功。被广泛使用的RMF理论忽略了同位旋矢量标量δ介子自由度。最近,有人利用拟合大量微观从头计算的结果将同位旋矢量矢量道和同位旋矢量标量道分离拟合出了一组包含δ介子的高精度参数DD-MEδ.本论文的主要工作是基于密度依赖的相对论平均场(DDRMF)理论,利用包含δ介子自由度的参数DD-MEδ与另三组广泛使用的不含δ介子的DDRMF模型参数DD.ME2,TW99,和PKDD,计算了一些核物质和中子星的性质,并详细讨论了δ介子对于非对称核物质高密区域状态方程的影响。结果表明同位旋矢量标量道会影响核子的有效质量和同位旋标量标量σ场从而软化非对称核物质的状态方程,并且会影响核物质对称能在高密区域的密度依赖行为。由于δ介子对核物质对称能的影响,DD-MEδ给出了较高的中子星内部质子比例,得到的质子比例足以支持质量大于1.86M⊙的中子星发生直接Urca过程。DD-MEδ参数给出的中子星的最大质量极限为1.97M⊙,这一结果与目前观测到的最重的中子星PSR J1614-2230(1.97±0.04 M⊙)和PSR J0348+0432'(2.01 ±0.04 M⊙)的质量恰好一致。在所选的几组参数中,DD-MEδ给出的中子星半径最小,1.4M⊙中子星的半径与目前的天文观测也十分相符。这一符合天文观测的结果证实了在相对论平均场模型框架下引入6介子的必要性。
[Abstract]:Neutron stars have been a hot research area in nuclear physics and astrophysics because of their extreme physical conditions. In the study of neutron stars, finding a suitable equation of state (EOS) has always been a long-term goal and central task. The equation of state of neutron star matter largely determines the mass radius relation of neutron star. However, there is still considerable theoretical uncertainty for the equation of state under high density, and the results given by different theoretical models are also very different. Moreover, recent studies show that the mass-radius relationship given by many theoretical models does not accord with astronomical observations, especially that the neutron star radius is generally larger. In recent decades, the relativistic mean field (RMF) theory has achieved great success in the fields of nuclear structure, nuclear reaction and nuclear astrophysics. The widely used RMF theory ignores the isospin vector scalar 未 meson degree of freedom. Recently, a group of high-precision parameters, DD-ME 未, containing 未 mesons, have been fitted separately from the isospin vector channel and the isospin vector scalar channel by using a large number of microcosmic ab initio calculations. The main work of this thesis is based on the density dependent relativistic mean field (DDRMF) theory, using the parameter DD-ME 未 which includes the degree of freedom of 未 mesons and the other three widely used DDRMF model parameters DD.ME2,TW99, and PKDD, without 未 mesons. The properties of some nuclear matter and neutron star are calculated, and the effect of 未 meson on the equation of state in the high density region of asymmetric nuclear matter is discussed in detail. The results show that the isospin vector scalar channel will affect the effective mass of the nucleon and the 蟽 field of the isospin scalar, thus softening the equation of state of the asymmetric nuclear matter, and will also affect the density dependent behavior of the symmetric energy of the nuclear matter in the high density region. Due to the effect of 未 mesons on the symmetric energy of nuclear matter, DD-ME 未 gives a higher proton ratio in neutron stars. The proton ratio obtained is sufficient to support the direct Urca process of neutron stars with a mass greater than 1.86m. The maximum mass limit of the neutron stars given by the DD-ME 未 parameter is 1.97m 298. The results are in good agreement with the mass of the heaviest neutron star PSR J1614-2230 (1.97 卤0.04M) and PSR J0348 0432'( 2.01 卤0.04M). Among the selected parameters, the radius of the neutron star given by DD-ME 未 is the smallest, and the radius of the 1.4 m ~ (-) ~ (*) neutron star is in good agreement with the present astronomical observations. The results obtained in accordance with astronomical observations confirm the necessity of introducing 6 mesons in the framework of the relativistic mean field model.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P145.6;O571

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