热核物质中基态关联修正下的单核子势和核子有效质量

以有限温度Brueckner-Hartree-Fock(BHF)方法为基础，利用质量算子的空穴线展开，计算了不同温度和密度下的核物质中单核子势和核子有效质量，特别是研究和讨论了基态关联效应和三体核力贡献对热核物质中单核子势的影响. 研究表明，基态关联和三体核力对单核子势的密度和温度依赖性均有重要影响. 基态关联导致的重排修正具有排斥性，大大减弱了低动量区域单核子势的吸引性，而且基态关联效应对单核子势的贡献随密度增大而增强，随温度升高而减弱. 三体核力对基态关联的影响是导致单核子势中重排项贡献减小. 在高密 关键词： 有限温度BHF方法 质量算子空穴线展开 重排修正 单核子势 有效质量     

三体核力重排效应对核物质中单核子平均场的贡献

在微观多体Brueckner-Hartree-Fock理论框架内, 实现了三体核力对核物质中单核子势的重排贡献的计算, 研究了三体核力重排贡献对单核子平均势场的动量相关性和密度依赖性的影响. 另外, 还计算了核物质中核子的有效质量并着重讨论了三体核力重排效应的影响. 结果表明: 三体核力对单核子势的重排贡献具有排斥性, 而且三体核力的重排效应随动量和密度的增加而迅速增强; 在高密度和高动量区域这一排斥贡献具有很强的动量相关性并起到了减弱单核子势吸引性和增强单核子势动量相关性的重要作用, 有助于澄清非相对论性BHF平均势场在高密度和高动量区域吸引性过强和动量相关性过弱的问题.     

三体核力重排项的同位旋效应

在同位旋相关的Brueckner理论框架内, 研究了三体核力重排贡献对同位旋对称势及其动量相关性和密度依赖性的影响，特别是研究了三体核力重排效应对于非对称核物质中质子和中子有效质量同位旋劈裂的影响. 结果表明: 三体核力重排效应对质子和中子单核子势均具有排斥性，而且其贡献随动量和密度增加而迅速增大. 在低密度区域，三体核力重排贡献对同位旋对称势的影响相当小，然而随着密度的升高，三体核力重排效应的贡献显著增强. 在高密度区域，三体核力重排效应使得同位旋对称势明显增大，而且当密度足够高时，三体核力重排贡献甚至导致对称势的动量相关性质发生改变. 三体核力的重排效应对核子有效质量同位旋依赖性的影响是使高密度丰中子核物质中质子-中子有效质量同位旋劈裂的幅度显著减小.     

对称核物质中核子-核子散射截面的研究

在扩展的Brueckner-Hartree-Fock (BHF)理论框架下, 采用Argonne V₁₄ 两体相互作用势研究了对称核物质中核子-核子散射的总截面和微分截面, 分别讨论了三体核力(TBF)重排效应和基态关联效应对全同和非全同核子散射截面的影响。 计算表明: 低动量区域的基态关联效应会导致介质中核子-核子散射截面的增大; 而随着密度的增加,TBF重排效应的逐渐加强会减小介质中的核子-核子散射截面。 The nucleon nucleon cross sections in symmetric nuclear matter were investigated in the framework of the extended Brueckner-Hartree-Fock(BHF) approach with Argonne V₁₄ two body interaction. The influences of the ground state correlation and the rearrangement contribution of the three body force (TBF) on the cross section have been obtained and discussed separately for identical and non identical nucleon collisions. It is shown that the magnitudes of the cross section are increased by the effects of the ground state correlation in low momentum transfers,and are suppressed in medium with increasing density when the rearrangement contribution of the TBF force is considered.     

热核物质液气相变的临界温度和三体核力效应

通过引入微观三体核力, 扩展了有限温度Brueckner-Hartree-Fock方法. 利用这一扩展的理论模型, 研究了热核物质的状态方程和液气相变现象并计算了临界温度, 讨论了三体核力对液气相变临界点性质的影响并与Dirac-Brueckner-Hartree-Fock方法的理论预言进行了比较. 结果表明：三体核力对热核物质状态方程提供一个随密度和温度增大而增强的排斥贡献, 而且三体核力的排斥效应导致热核物质液气相变的临界温度明显降低.     

核物质中的三体核力效应和相对论效应

在BHF理论框架内,利用两体现实核力和微观三体核力研究了核物质状态方程,仔细计算和分析了核介质中不同的基本微观过程导致的三体核力对核物质状态方程的贡献,与相对论DBHF方法的计算进行了比较.结果表明,DBHF方法中包含的对核物质状态方程的主要相对论修正来自于核介质中伴随着自由核子–反核子对虚激发中间过程对核子相互作用中标量σ介子交换过程介质修正效应所导致的三体核力,而来自于其他的基本微观过程的三体核力对核物质状态方程的贡献并不能完全相互抵消,它们的总贡献甚至在饱和密度附近也是不能忽略的     

同位旋非对称核物质性质与扩展的BHF方法(Ⅶ)中子星物质中质子和中子的1S0态超流性

利用Brueckner-Hartree-Fock和BCS理论方法,计算了β稳定中子星物质中处于 1S0态的质子和中子的对关联能隙,着重研究和讨论了三体核力的影响.结果表明三体核力对β稳定中子星物质中 1S0态中子超流性的影响相对较小,但对 1S0态质子超流性具有重要影响,而且其效应随核子数密度增大而迅速增强.三体核力的主要作用是强烈地抑制了高密度β稳定中子星物质中的 1S0态质子超流性.     

非对称核物质中质子和中子的1S0态超流性

利用Brueckner-Hartree-Fock和BCS理论方法,计算了非对称核物质中处于1S0态的质子和中子的对关联能隙,着重研究和讨论了能隙的同位旋依赖性和三体核力的影响.结果表明:随核物质的同位旋非对称度增大,中子1S0态超流相存在的密度范围逐渐缩小而且对关联能隙峰值稍有升高;质子1S0态超流相存在的密度范围迅速扩大而且对关联能隙峰值显著降低.三体核力对非对称核物质中1S0态中子超流性及其同位旋依赖性的影响相对较小,但对1S0态质子超流性具有重要影响,而且其效应随核子数密度增大而迅速增强.三体核力的主要作用是强烈地抑制了具有高非对称度的核物质中高密度区域的1S0态质子超流性,导致质子超流相存在的密度范围显著缩小.     

非对称核物质中同位旋对称势的动量和密度依赖性

在Brueckner-Hartree-Fock理论框架内, 研究了同位旋非对称核物质中质子和中子单粒子势的动量相关性及其随同位旋非对称度的变化, 在此基础上计算了同位旋对称势, 并讨论了三体核力的影响. 结果表明同位旋对称势对于同位旋非对称度的依赖性很弱, 但对于动量和密度均有较强的依赖性. 当密度固定时, 同位旋对称势随动量增加而减小. 尽管三体核力对于质子和中子单粒子势的动量相关性有较大影响, 但对同位旋对称势的影响很小. 还与目前重离子碰撞输运理论模型中所使用的各种参数化的唯象对称势进行了比较.     

新生中子星的性质与三体核力效应

在Brueckner-Hartree-Fock理论框架内, 研究了新生中子星的状态方程和性质, 计算了新生中子星的最大质量和新生中子星中质子占总核子数的丰度, 特别是讨论了三体核力和中微子束缚效应的影响以及三体核力和中微子束缚效应的相互影响. 结果表明, 无论是否考虑三体核力, 中微子束缚对新生中子星的状态方程和质子丰度均有明显影响. 中微子束缚导致新生中子星物质中的质子丰度显著增大. 三体核力的贡献是使新生中子星的状态方程变硬并导致新生中子星中质子丰度明显增大. 束缚在中子星物质中的中微子显著减弱了三体核力对于中子星物质中质子丰度的影响.     

Nucleon effective mass in symmetric nuclearmatter from the extended Brueckner-Hartree-Fock approach

We have calculated the nucleon effective mass in symmetric nuclear matter within the framework of the Brueckner-Bethe-Goldstone (BBG) theory, which has been extended to include both the contributions from the ground-state correlation effect and the three-body force (TBF) rearrangement effect. The effective mass is predicted by including the ground-state correlation effect and the TBF rearrangement effect, and we discuss the momentum dependence and the density dependence of the effective mass. It is shown that the effect of ground state correlations plays an important role at low densities, while the TBF-induced rearrangement effect becomes predominant at high densities.     

Symmetry energy,unstable nuclei and neutron star crusts

We present an upgraded review of our microscopic investigation on the single-particle properties and the EOS of isospin asymmetric nuclear matter within the framework of the Brueckner theory extended to include a microscopic three-body force. We pay special attention to the discussion of the three-body force effect and the comparison of our results with the predictions by other ab initio approaches. Three-body force is shown to be necessary for reproducing the empirical saturation properties of symmetric nuclear matter within nonrelativistic microscopic frameworks, and also for extending the hole-line expansion to a wide density range. The three-body force effect on nuclear symmetry energy is repulsive, and it leads to a significant stiffening of the density dependence of symmetry energy at supra-saturation densities. Within the Brueckner approach, the three-body force affects the nucleon s.p. potentials primarily via its rearrangement contribution which is strongly repulsive and momentum-dependent at high densities and high momenta. Both the rearrangement contribution induced by the three-body force and the effect of ground-state correlations are crucial for predicting reliably the single-particle properties within the Brueckner framework.     

Δ(3, 3) excitations and effective three-nucleon forces in finite nuclei

Contributions from three-body terms with intermediate Δ(3,3) isobar excitations to the ground state energies of nuclei are investigated. These terms can either be understood as three-body clusters in a many-body theory including isobar excitations explicitly or as contributions to an effective three-nucleon force. For the example ¹⁶O the resulting contribution is attractive and its value is typically about ?0.5 MeV per nucleon. This is smaller than the typical values of 1 MeV per nucleon repulsion obtained from the modifications of the effective two-body nucleon-nucleon interaction in nuclei due to intermediate Δ(3, 3) configurations. The gain in energy from the three-body terms including Δ(3,3) configurations, however, is of the same importance as the contribution from three-body terms including nucleons only.     

Decomposition of the equation of state of asymmetric nuclear matter into different spin-isospin channels

We investigate the equation of state of asymmetric nuclear matter and its isospin dependence in various spin-isospin ST channels within the framework of the Brueckner-Hartree-Fock approach extended to include a microscopic three-body force (TBF). It is shown that the potential energy per nucleon in the isospin-singlet T=0 channel is mainly determined by the contribution from the tensor SD coupled channel. At high densities, the TBF effect on the lsospin-triplet T=1 channel contribution turns out to be much larger than that on the T=0 channel contribution. At low densities around and below the normal nuclear matter density, the isospin dependence is found to come essentially from the isospin-singlet SD channel and the isospin-triplet T=1 component is almost independent of isospin asymmetry. As the density increases, the T=1 channel contribution becomes sensitive to the isospin asymmetry and at high enough densities its isospin dependence may even become more pronounced than that of the T=0 contribution. The present results may provide some microscopic constraints for improving effective nucleon-nucleon interactions in a nuclear medium and for constructing new functionals of effective nucleon-nucleon interaction based on microscopic many-body theories.     

Critical Temperature of Lequid-gas Phase Transition for Hot Nuclear Matter and Three-body Force Effect

The finite temperature Brueckner-Hartree-Fock (FTBHF) approach is extended by introducing a microscopic three-body force. Within the extended approach, the three-body force effects on the equation of state of hot nuclear matter and its temperature dependence have been investigated. The critical properties of the liquid-gas phase transition of hot nuclear matter have been calculated. It is shown that the three-body force provides a repulsive contribution to the equation of state of hot nuclear matter. The repulsive effect of the three-body force becomes more pronounced as the density and temperature increase and consequently inclusion of the three-body force contribution in the calculation reduces the predicted critical temperature from about 16MeV to about 13MeV. By separating the contribution originated from the 2σ-exchange process coupled to the virtual excitation of a nucleon-antinucleon pair from the full three-body force, the connection between the three-body force effect and the relativistic correction from the Dirac-Brueckner-Hartree-Fock has been explored. It turns out that the contribution of the 2σ-NN part is more repulsive than that of the full three-body force and the calculated critical temperature is about 11MeV if only the 2σ-NN component of the three-body force is included which is lower than the value obtained in the case of including the full three-body force and is close to the value predicted by the Dirac-Brueckner-Hartree-Fock (DBHF) approach. Our result provides a reasonable explanation for the discrepancy between the values of critical temperature predicted from the FTBHF approach including the three-body force and the DBHF approach.     

同位旋非对称核物质性质与扩展的BHF方法(Ⅴ)三体核力对质子和中子单粒子势的影响

在扩展的同位旋相关的Brueckner Hartree Fock理论框架内,研究了三体核力对同位旋非对称核物质中质子与中子的单粒子势及其同位旋依赖性的影响.