Effect Of σ～* And ф Mesons On Neutron Star Matter

In this thesis, With the relativistic mean-field (RMF) approach considering the baryon octet, properties of neutron star matter have been investigated. It is mainly studied that how theσ^*,φmesons affect the properties of the zero temperature neutron star, the finite temperature neutron star and the rotating neutron star.For the zero temperature neutron star, the results calculated by us are as follows.As the baryon density arriving at 0.4 fm^-3, theσ^*,φmesons appear. Afterwards their field strength rise with the baryon density increasing and the interaction between hyperons become stronger. So the contribution ofσ^*,φmesons makes the threshold of∑⁰,Ξ⁰,∑⁺ hyperons lower (but forA hyperons, the effect is not obvious) and the relative number density of hyperons increase more quickly and considering the neutrality the e,μ^-,p's relative number density decrease more quickly. Because the contribution ofσ^*,φmesons make more neutrons decay to hyperons the relative number density of neutrons will decrease more heavily and the transition density of hyperon starsρ_0H become lower. Forσ,ω,ρmesons, their field strength become lower too considering the effect ofσ^*,φmesons. In addition, the appearance ofσ^*,φmesons makes the freedom degree increase and therefore the Fermi moment of the system decrease. Soσ^*,φmesons also make the chemical potential of proton and electron lowerThe effect ofσ^*,φmesons on equation of state is also obvious. From the results calculated by us, we can see that the pressure increase with the centre energy density growing. Considering the contribution ofσ^*,φmesons, the pressure increases more quickly and the equation of state is softened. Theσ^*,φmesons also make the maximum mass be smaller while the corresponding radius be longer. At the same time, the centre energy density decrease more quickly and dose the centre pressure because of the contribution ofσ^*,φmesons.As for the effect of temperature on neutron star matter, our results are as follows too(in our calculation, the interaction of hyperons are considered and the temperature points are selected as T=5MeV, IOMeV, 15MeV, 20MeV, 25MeV). (a) Effect of temperature on meson field strength.In the lower baryon density region (ρ=0.3～0.7fm^-3), the field strength ofσ^*,φmesons is great than zero earlier as the temperature is higher. In the middle baryon density region (ρ=0.7～1.2fm^-3), the effect is not obvious. As the baryon density rising up to the region(ρ＞1.2fm^-3), the field strength ofσ^* mesons reduce with the baryon density increasing but forφmesons the effect is not obvious. For the field strength ofσ,ωmesons, in the lower baryon density region (ρ＜0.3fm^-3), temperature almost dose not effect the field strength ofσ,ωmesons. In the baryon density regionρ＞0.3fm^-3, the field strength ofσ,ωmesons decreases as the temperature increase. For the neutron chemical potential, it decreases as the temperature increase. But for electron chemical potential, the effect of temperature on it is more complicated. In the lower baryon density region (0＜ρ＜0.2fm^-3), it rises as the temperature increase. In the middle baryon density region (0.2fm^-3＜ρ＜0.9fm^-3), it rdecreases as the temperature increase. In the high baryon density region (ρ＞0.9fm^-3), there is almost no effect.(b) Effect of temperature on particle relative number density.For neutrons, their relative number density become lower as the temperature is higher.For protons, in the lower baryon density region(ρ＜0.37fm^-3), their relative number density is higher as the temperature become higher. In the baryon density region(ρ＞0.37fm^-3), the effect is not obvious.For electron andμ, in the lower baryon density regionρ＜0.37fm^-3, their relative number density is higher as the temperature increasing. In the middle baryon density region(0.37fm^-3＜ρ＜0.66fm^-3), their relative number density reduce greatly as the temperature increasing. In the higher baryon density region(ρ＞0.66fm^-3), their relative number density reduce slowly with the temperature increasing.ForΛ,Ξ^-hyperons, there is a turning point respectively.(Λ～0.48fm^-3,,Ξ^-～0.67fm^-3), below which their relative number density rise with the temperature increasing but beyond which their relative number density reduce with the temperature increasing. For∑^-,∑⁰,Ξ⁰,Σ⁺ hyperons, their relative number density rise with the temperature increasing. For all the six kinds of hyperons above, higher temperature greatly decrease their thresholds.(c) Effect of temperature on equation of state.For a same centre energy density, as the temperature rising the pressure and the mass increase and the effect is more obvious in the lower centre energy density region. For the relationship between mass and r.adius, at a same mass the corresponding radius become longer as the temperature rising.Afterwards, the effect ofσ^*,φmesons on finite temperature neutron star matter is as follows. Here, the temperature is T=15MeV.It is the same as the case of the zero temperature neutron star. Theσ^*,φmesons field strength are more than zero as the baryon density arriving at 0.34 fm^-3. Afterwards, it rise with the baryon density increasing. and the interaction between hyperons become stronger. So the contribution ofσ^*,φmesons makes the threshold of∑⁰,Ξ⁰,∑⁺ hyperons lower (but forΛhyperons, the effect is not obvious) and the relative number density of hyperons increase more quickly and considering the neutrality the e,μ^-,p's relative number density decrease more quickly. The contribution ofσ^*,φmesons also make the equation of state soft, the maximum mass smaller while the corresponding radius longer., the centre energy density and the centre pressure decrease more quickly.The conclusion mentioned above represents the case of real stable neutron star matter only in the baryon density region ofρ≤ρ_c.As for the case ofρ＞ρ_c, our results only have theory meaning.Our calculation about the rotating neutron star are as follows.The contribution ofσ^*,φmesons, the higher temperature, the larger compression modulus K and the larger symmetry energy coefficient a_sym will makes the moment of inertia larger.It is also can be seen from our calculation that the maximum mass and the maximum moment of inertia are not arriving at their respective maximum at the same centre energy density.