强磁场下中子星状态方程的理论研究

发布时间：2018-04-10 11:51

本文选题：中子星 + 状态方程　；参考：《南京大学》2017年硕士论文

【摘要】：中子星因其极高的密度和其他极端条件而成为检验极端条件下物理理论的天然实验室。其中,中子星的状态方程是天体物理领域的一个热点问题。状态方程直接影响了中子星的结构。将状态方程作为输入,求解由广义相对论得到的TOV方程,即可得到中子星的质量-半径关系。观测发现,很多中子星表面的磁场高达1014-1015G,高于临界磁场强度4.414×1013G。朗道量子化将对电子的能级产生显著影响。因此,磁场可对中子星的状态方程产生很大影响。在强磁场下,反常磁矩也可影响中子星的性质。磁场的能量动量张量是各向异性的。在这种情况下,TOV方程是不适用的。然而,之前的很多工作忽略了这个问题。2015年Lopes等人提出的混沌磁场近似为解决这个问题提供了一种途径。另外,中子星内部磁场变化情况目前仍不清楚。目前,多数文献假设磁场依赖于重子数密度。然而,这远非确定。我们也可以假设磁场依赖于能量密度。相对论平均场论能极大的简化计算,因而在核物理中得到了广泛应用。相对论平均场论在中子星状态方程的研究方面取得了较大成功。FSUGold模型是相对论平均场论框架下一个较合理的模型,可以成功重复出许多有限核的基态性质。被扩展到包含超子的FSUGold模型已成功被用于中子星状态方程的研究。然而,之前的工作未能将磁场和反常磁矩的影响纳入考虑。本文的结构是这样的:第一章简单介绍了中子星的相关背景知识,和利用相对论平均场论对中子星状态方程的研究现状。第二章介绍了利用相对论平均场论研究中子星状态方程的理论框架。我们对FSUGold模型作了简单介绍,描述了TOV方程和磁场导致的朗道量子化,阐释了使用混沌磁场近似的理由,介绍了重子数密度依赖磁场模型和能量密度依赖磁场模型,对自旋极化也做了介绍。第三章计算了能量密度依赖磁场下中子星的性质。我们发现非混沌磁场使状态方程硬化许多,对中子星最大质量提高也很多。混沌磁场下的状态方程比无磁场的硬,但是比非混沌磁场下的软,所以混沌磁场下得到的最大质量也介于两者之间。反常磁矩对状态方程影响很小,对中子星最大质量影响也很小,但是它对自旋极化影响较大,特别是电中性费米子因反常磁矩而发生自旋极化。第四章计算了重子数密度依赖磁场下中子星的性质,同样发现混沌磁场下的中子星性质介于无磁场和非混沌磁场之间。反常磁矩也同样主要影响自旋极化。最后一章对我们的理论研究做了一个简短的总结,并对未来的工作做了展望。
[Abstract]:Neutron stars, due to their extremely high density and other extreme conditions, have become natural laboratories for testing physical theories under extreme conditions.Among them, the equation of state of neutron stars is a hot issue in the field of astrophysics.The equation of state directly affects the structure of neutron stars.The mass-radius relation of neutron stars can be obtained by solving the TOV equation derived from general relativity by taking the equation of state as input.Landau quantization will have a significant effect on the energy levels of electrons.Therefore, the magnetic field can have a great influence on the equation of state of neutron star.Under strong magnetic field, anomalous magnetic moment can also affect the properties of neutron stars.The energy and momentum of the magnetic field Zhang Liang is anisotropic.In this case, the TOV equation is not applicable.However, a lot of previous work has ignored the problem. The chaotic magnetic field approximation proposed by Lopes et al in 2015 provides a way to solve the problem.In addition, the variation of the magnetic field inside the neutron star is still unclear.At present, most literatures assume that the magnetic field depends on the baryon number density.However, this is far from certain.We can also assume that the magnetic field depends on energy density.Relativistic mean field theory can greatly simplify the calculation, so it is widely used in nuclear physics.The relativistic mean field theory has achieved great success in the study of neutron star equation of state. The FSUGold model is a more reasonable model under the framework of relativistic mean field theory, and the ground state properties of many finite nuclei can be successfully repeated.The FSUGold model, which is extended to include hyperons, has been successfully used in the study of neutron star equation of state.However, previous work has failed to take into account the effects of magnetic fields and anomalous magnetic moments.The structure of this paper is as follows: the first chapter briefly introduces the background knowledge of neutron stars and the research status of neutron star equation of state using relativistic mean field theory.The second chapter introduces the theoretical framework for the study of neutron star equation of state using relativistic mean field theory.We briefly introduce the FSUGold model, describe the TOV equation and the Landau quantization caused by the magnetic field, explain the reason of using chaotic magnetic field approximation, introduce the baryon density dependent magnetic field model and the energy density dependent magnetic field model.Spin polarization is also introduced.In chapter 3, the properties of neutron stars in energy density dependent magnetic field are calculated.We find that the nonchaotic magnetic field harms the equation of state and increases the maximum mass of neutron stars.The equation of state in the chaotic magnetic field is harder than that in the non-magnetic field, but it is softer than that in the non-chaotic magnetic field, so the maximum mass obtained in the chaotic magnetic field is somewhere between the two.The anomalous magnetic moment has little effect on the equation of state and the maximum mass of neutron star, but it has a great influence on the spin polarization, especially on the electric neutral fermion spin polarization due to the anomalous magnetic moment.In chapter 4, we calculate the properties of neutron stars under baryon density dependent magnetic field. We also find that the properties of neutron stars in chaotic magnetic field are between non-magnetic field and non-chaotic magnetic field.Anomalous magnetic moments also mainly affect spin polarization.The last chapter makes a brief summary of our theoretical research and prospects for future work.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P145.6

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