| Due to the extremely high density and other extreme conditions in neutron stars,they are natural laboratories to test physical theories under extreme conditions.The equation of state(EOS)is one of the hot topics in astrophysics.EOS directly influ-ences the structure of neutron star.Using equation of state as input to solve the TOV equation which is derived from General Relativity,we can get the mass-radius relation of neutron star.According to observations,there exist magnetic fields as high as 1014-1015 G on the surface of many neutron stars,higher than the critical field strength Bce=4.414×1013 G.The energy spectra of electron will be influenced significantly by Landau quantization.Therefore it is possible for magnetic field to have a significant influence on the EOS of neutron star.The anomalous magnetic moments(AMM)may also influence properties of neutron star under strong magnetic fields.The energy-momentum tensor for magnetic field is anisotropic.In this situation,the TOV equation is not applicable.However,many previous works ignored this prob-lem.The chaotic field approximation proposed by Lopes et al.in 2015 provides a way to solve the problem.Furthermore,it is still unclear how magnetic fields vary in the interior of neutron star.Most papers suppose that magnetic fields depend on baryon number density.However,this is far from certain.We could suppose magnetic fields depend on energy density instead.The relativistic mean field(RMF)theory is widely used in nuclear physics as it can greatly simplify calculations.Much success has been achieved in its application to the study of the EOS of neutron star.The FSUGOld model is a well-established mod-el within the framework of the RMF theory,which is able to reproduce ground-state properties of many finite nuclei.The model extended to hyperons has been successful-ly used to study the EOS of neutron star.However,the effects of magnetic field and AMM have been neglected.The thesis is organised as follows:in Chapter 1,we provide some useful back-ground information about neutron stars,and describe current studies of the EOS of neutron star using RMF theory.In Chapter 2,the framework of the RMF theory applied to the study of the EOS of neutron star is presented.We briefly describe the FSUGOld model,then present the TOV equation and Landau quantization caused by magnetic fields.The reason why we should use the chaotic field approximation is explained.We also introduce the bary-on number density-dependent magnetic field model and the energy density-dependent magnetic field model.At last we give a brief introduction to spin polarization.Chapter 3 is devoted to obtained results about properties of neutron star employing the energy density-dependent magnetic field model.We find that the EOS is stiffened significantly by the presence of magnetic field when not using the chaotic field approx-imation,the maximum mass of neutron star is also greatly increased.The EOS includ-ing magnetic field and using the chaotic field approximation is stiffer than the field-free case,but softer than the EOS including magnetic field and not using the chaotic field approximation,the maximum mass of neutron star obtained is also between the two cases.The AMM only have a small influence on the EOS and the maximum mass,but have a large influence on the spin polarization of fermions,in particular,neutral fermions are spin polarized due to the presence of the AMM.In Chapter 4,we perform some calculations about properties of neutron star using the baryon number density-dependent magnetic field model.It is shown that properties of neutron star including magnetic field and using the chaotic field approximation are between the field-free case and the case including magnetic field but not using the chaotic field approximation too.The AMM mainly influences spin polarization.In the last chapter,we summarize our theoretical research,and give some outlooks on our future works. |
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