Research On Strange Particles Of Neutron Star In Relativistic Mean Field Theory

With central density exceeding several times the nucleus density,neutron star is the densest macroscopic objects in the universe.Therefore,they are unparalleled natural laboratories that allow us to investigate the constituents of matter and their interactions under extreme conditions that cannot be reproduced in any terrestrial laboratory.The global properties of neutron stars(mass,radius,moment of inertia,surface gravitational redshift,etc.)and their internal composition(species of constituent particles and possible different phases of matter)primarily depend on the equation of state of strong interacting matter,i.e.,the thermodynamical relation between the matter pressure,energy density,and temperature Determining the correct equation of stat for describing the properties of neutron stars is a fundamental problem in nuclear physics and particle physics as well as astrophysics.As mentioned before,due to their large central densities,various "exotic" constituents,for example hyperons which will soften equation of state are expected in neutron star interiors But the recent measurements of PSR J1614-2230 and PSR J0348+0432 suggested that the upper limit of the neutron star mass could be larger than2 M.The existence of strange particles in such massive neutron stars is an important and puzzling problem that needs in-depth study.In this paper,under the framework of relativistic mean field theory,we study the strange particles in the matter of massive neutron stars,and mainly discuss the phases of hyperonsFirstly,using the relativistic mean field theory,seven different nucleon coupling parameter sets,GL85,GL97,GM1,TM1,DDMEI,NLSH and TM2,are selected to analyze the appearances of hyperons and transformation density in the cold neutron star matter.We found that TM2 have the largest proportion of A-hyperon,the relative proportions of A-hyperons of parameter sets GM1,GL85,and GL97 are relatively small;the parameter sets DDMEI and NLSH have larger proportions of ?--hyperon and ?0-hyperon,and the relative proportions of ?--hyperon of GL97 and TM1 are relatively small.The results show that the relative proportions of total hyperons of GL85,GM1 and TM1 are relatively small,and the transformation density are relatively large;while DDMEI,NLSH and TM2 have relatively large relative proportions of total hyperons,and the transformation density are relatively small.In addition,we also study the influences of nuclear coupling parameters on different meson fields and chemical potentials,and the meson field and chemical potential of different parameter sets are very different.For instance,the field strengths of ?-meson and co-meson and chemical potential of neutron of the parameter sets DDMEI and NLSH are relatively large,the field strengths and chemical potential of GL85 and GL97 are relatively small.The field strengths of p-meson and chemical potential of electron of parameter sets DDMEI and NLSH are relatively small,while the value of GL85 and GL97 parameter sets are relatively large.Then,under the framework of relativistic mean field theory,the nucleon coupling parameter set GL85 and the appropriate hyperon coupling parameters are selected with considering the strange mesons ?*and ?,and the coupling parameters of the scalar meson ?*are selected according to SU(6)symmetry and potential depths,respectively.The properties of the cold neutron star are first studied.The maximum mass of the neutron stars we calculated exceeds 2 M,so these parameters are extrapolated to study the effects of strange mesons ?*and ? on the properties of massive protoneutron stars at different stages of evolution.When the coupling parameters of the ?*meson were determined by SU(6)symmetry,the field strength of ?*is smaller than the field strength of ?,that is,the repulsive force between hyperons is greater than the attractive force in three different evolution stages of the protoneutron star,while when the coupling parameters of ?*meson are were determined by potential depths,the repulsive force between the hyperons is smaller than the attractive force in three evolution stages.Compared with not considering the ?*and? mesons,when the coupling parameters of the ?)meson were determined by SU(6)symmetry,the relative proportion of hyperons becomes smaller and the relative proportion of nucleons is larger.The temperature of the protoneutron stars matter is higher and the equation of state is stiffer,the calculated maximum mass is larger.However,when the coupling parameters of ?*are determined by potential depths,the calculation results obtained are different.Compared with not considering the ?*and ? mesons,the relative proportion of nucleons is smaller and the relative proportion of hyperons is larger.The temperature of the protoneutron stars matter is lower and the equation of state is softer,the calculated maximum mass is lower.The properties of the protoneutron stars whose mass is the same as that of PSR J0348+0432 in different evolution stages were also presented.Finally,we study the relationship between the saturation properties of nuclear matter and the maximum mass of neutron stars.It is seen that the binding energy per baryon number B/A and the symmetry energy coefficient asym have little influence on the mass of neutron stars,and by way of contrast,the nuclear saturation density ?0 affect the neutron star mass substantially.We currently have relatively little understanding about the effective mass m and compression modulus K.Therefore,it is necessary for us to further study the influences of the nuclear saturation density ?0,the effective mass m and the compression modulus K on the neutron star mass.The results show that if compression modulus K>303MeV,effective mass m*<0.6,and nuclear saturation density ?0<0.14 fm-3,we can obtain massive neutron stars with mass exceeding 2 M.From our calculations,we can find that when there are hyperons in neutron star matter,the maximum mass obtained can exceed 2 M even without breaking the SU(6)symmetry.That is to say,under the condition of certain saturation properties of nuclear matter,hyperons can appear in the interior of a massive neutron star,which rends the hyperon puzzle to be solved.