Study On The Effects Of Hyperons In Massive Neutron Stars

Neutron stars are a class of very dense stars in astronomy,with masses between white dwarfs and black holes.The core density is close to or even higher than the density of saturated nuclear matter,and the rotation speed is extremely fast.From the formation to the final-cooling process,the emitted electromagnetic spectrum includes various electromagnetic wave bands ranging from extremely high-energy gamma-ray bursts and X-ray bursts to low-energy spectra.Nowadays,the research of neutron s-tars is no longer based on optical electromagnetic bands to obtain information.With the development of multi-messenger astronomical observation methods,we have been able to comprehensively describe neutron star physics from four aspects,namely grav-itational wave signals of gravitational interaction,neutron star rotating pulse signals of electromagnetic interaction,and internal Neutrino signals of weak interaction,as well as internal nuclear interaction signals of strong interaction.The mass of a neutron star is generally limited to a range.The lower limit mass is called the Chandrasekhar mass limit.Below this mass,a neutron star cannot be formed and evolves into a white dwarf.The upper limit is called the Oppenheimer mass limit,above this limit,the stars will inevitably collapse into black holes.Before 2010,under the insufficient observation conditions,the mass of neutron stars is generally considered to be at about 1.5 times the mass of the sun,and the radius is between 11 km and 12km.The work during this period mainly focused on the research of the equation of state.Initially,neutron stars were considered to be composed of uniform nuclear matter,then the properties of symmetric nuclear matter were used to speculate the properties of neutron stars'asymmetric nuclear matter and study the effects of symmetry energy on neutron stars.Subsequent research found that it is obviously unreasonable to treat neutron stars as homogeneous nuclear material spheres.It is generally believed that neutron stars may also have a shell structure like an atomic nucleus,which is divided into shell regions and core regions.Due to the relatively low density of the outer layer,it is composed of atomic nuclei and free electron Fermi gas.In this area,the current research is relatively clear.For the inner shell,the density is near the density of nuclear matter and this area involves neutron dropline physics,neutron superfluid physics,and the possible existence of Pasta phase transition physics.There have been many good works in this area recently.Compared with the shell region,the physics of the core region has more uncertainty and challenge.Due to its high density,the nucleus no longer exists in the nuclear layer region,but it may not be neutrons and protons instead.There may be a?balance composed of free neutrons,protons,electrons,and?.High density may also allow protons to become su-perconductors,and may also cause nucleus to undergo a supernuclear phase transition into a hyperons.It may even form boson condensates,and the quark material may be unblocked from the nucleus.Some researchers even believe that there may exist the strangeon matter.Of course,it is more reasonable to think that those material forms can coexist.With so many possible matter forms and shell matter,it is difficult to construct a unified equation of state to describe the entire neutron star.On the contrary,we can only rely on models to describe the internal matter of neutron stars.For the area where baryon material exists,there are two research directions.One is the phenomenological-microscopic model,which uses the mean field based on Skyrme interaction or the rel-ativistic mean field based on meson exchange.The theory that describes the properties of neutron stars can mostly satisfy the relevant characteristics of nuclear matter.A more favorable description is based on the micro-many-body Brueckner-Hartree Fock theory,and the relativity Dirac-Brueckner.Compared to the relativistic mean field the-ory,Brueckner theory absorbs the Brueckner-Bethe-Goldstone expansion.It also could handle three-body nucleus well,and has an advantage in describing superunclear neu-tron stars.The other direction is to start from the actual nuclear force and deduce from scratch.It is ideal to deal with the problem of fewer bodies.Once you deal with the problem of many bodies,the amount of calculation will increase exponentially.For the regions involving the existence of quark phases,especially high-energy free quark-s,the best theory that can describe their asymptotic freedom and quark confinement effect is of course quantum chromodynamics,but it is difficult to achieve such a high density in a neutron star.It is generally believed that the neutron stars may have a quark phase transition,and it has a strong model dependence.The earliest model was the MIT pocket model.The baryon is composed of three quarks,and the vacuum pressure in-side the pocket is constant.The MIT pocket model can explain the quark confinement effect,but cannot describe the asymptotic freedom.Further optimized models include the quark-meson coupling model based on baryon interactions through the exchange of mesons between quarks,and the Nambu–Jona-Lasinio model based on chiral symmetry breaking theory.Although multiple messenger astronomical methods have been developed,espe-cially the GW170817 gravitational wave event in recent years,it has brought unprece-dented opportunities to the neutron star physics.But recent astronomy has continuously observed the existence of massive neutron stars,from the discovery of the massive neu-tron star PSR J1614-2230 in 2010 to the existence of more than twice the solar mass neutron star PSR J0348+0432 in 2013,and then to the determination of the 2.14 times solar mass of the 2019 millisecond pulsar MSP J0740+6620,these facts have brought unprecedented challenges to neutron star physics.How to determine the morphology of matter inside the neutron star,and how to determine its interaction and construct the equation of state under the premise of this state of matter,as well as how to make the obtained equation of state that can support such a large neutron star mass and meet the data of astronomical observations.Both of them are very challenging.This thesis is mainly considered the uncertain factors of the state equation of neu-tron stars.In the framework of relativistic mean field theory,we have studied the influ-ence of supernuclear matter on the internal structure of neutron stars and constructed an equation of state capable of describing the internal structure of massive neutron s-tars.The first chapter of the paper is a background introduction to the neutron star,including his discovery and research process.It also describes the material structure of the neutron star from the outer shell to the inner core layer,finally it introduces the latest research progress of the neutron star.The second chapter of the thesis briefly in-troduces the research history of nuclear many-body physics,and deduces in detail how to obtain the EOS and mass-radius relationship of a neutron star under the theory of relativity mean field.The third chapter of the paper considers additional supernuclear interactions and introduces two strange mesons?and?~*.Prior to this,descriptions of neutron stars focused mainly on nuclear matter in the shell region,and most of the difficulties in the study of internal supernuclear matter lies in the inability to explain the phenomenon of hyperon puzzle.We consider the extra strange vector mesons?and scalar mesons?~*in the interaction of supernuclear matter,and consider the ther-mal effects of neutron stars.By selecting the appropriate parameter sets to study the properties of PSR J0348+0432,we can get good results and give various values?of PSR J0348+0432.This result can well avoid the phenomenon of hyperon puzzle.In the fourth chapter of the paper,in view of the many uncertainties in the current coupling sets of hyperon-hyperon interactions,and the values can only be obtained by fitting various properties near the density of nuclear matter,we construct two new hyperon-hyperon coupling sets named the hyperon limit model and the hyperon potential well depth model.Using them to describe the properties of the massive neutron star PSR J0348+0432,and to describe their similarities and differences.At the same time,we give the neutron star mass ranges that can be described by these two hyperon coupling parameter models.Finally,a comprehensive review summarizes the research content of this thesis.We also analyze and ponder the problems that arise during the research,and make a feasible outlook for future research based on this work.