相对论核多体理论中的自洽问题和求和规则

着重讨论了建立在相对论平均场基态上的相对论无规位相近似的自洽处理 .自洽处理要求基态和巨共振激发态的研究从同一个拉氏量出发,采用同一种建立在相对论下的完备基上的近似 .同时也讨论了自洽条件下Dirac海核子态的作用 ,指出 Dirac海核子态的贡献不能忽略 ,特别是在核的巨单极共振的情况.用约束的相对论平均场方法得到核的巨单极共振的能量逆权重的求和规则 ,从数值上验证了 Dirac海核子态的贡献. A consistent treatment is extremely important in relativistic approaches. We emphasized the consistent approach in relativistic random phase approximation built on relativistic mean filed ground states. The consistent treatment requires that the studies of the ground state and excited states of giant resonances are based on same effective Lagrangian, and on a same complete set of basis. It was found that the effect of the Dirac states could not be neglected, especially in the case of giant...     

相对论无规位相近似

讨论了建立在相对论平均场基态的相对论无规位相近似研究中的一致性问题. 研究表明考虑费米海和Dirac海的粒子 空穴激发对核的同位旋标量巨共振的能量有很大的影响. The fully consistent relativistic random phase approximation (RRPA) built on the relativist mean field (RMF) ground state is presented. The fully consistent RRPA requires that the nuclear RMF wave function and the RRPA renormalization are calculated in a same effective Lagrangian. A theoretically complete treatment of the RRPA at the mean field level with no sea approximation must include not only the usual particle hole states, but also the pairs formed from the occupied Fermi states and Dirac states. Effects of inclusion of Dirac sea states in various multipole excitations are investigated. Considerable effects on the isoscalar giant multipole resonances are observed.     

稳定和不稳定核巨共振性质的相对论研究

在相对论平均场的基态上自洽的相对论无规位相近似(RRPA)理论框架下,研究稳定核和不稳定核的巨共振性质.研究了稳定核²⁰⁸Pb,¹⁴⁴Sm,¹¹⁶Sn,⁹⁰Zr,⁴⁰Ca,¹⁶O和不稳定核Ca同位素链同位旋标量和同位旋矢量集体巨共振激发,并讨论了Dirac海负能核子态和矢量介子空间分量对核的巨共振性质的影响.研究的结果表明,Dirac海负能核子态和矢量介子空间分量对同位旋标量激发有贡献,特别是对重核,而对轻核它的贡献减弱,对于同位旋矢量激发的贡献可忽略.几组常用的相对论平均场非线性模型参量,不仅能成功的描述有限核的基态性质,也能很好地描述核的巨共振激发.对于N/Z极端情况下,同位旋矢量巨偶极激发模式存在低能集体激发,它是由于费密面附近弱束缚核子的激发和同位旋混杂效应 关键词： 相对论无规位相近似 核巨共振     

巨单极共振和对称能

基于带有混合同位旋标量-矢量非线性耦合的有效拉格朗日量, 在完全自洽的相对论无规位相近似的框架内, 通过单极压缩模式讨论了核物质的不可压缩性. 比较核²⁰⁸Pb,¹⁴⁴Sm,¹¹⁶Sn和⁹⁰Zr实验和计算的巨单极共振能量, 给出了核物质不可压缩系数的取值范围. 新的同位旋标量-矢量非线性耦合软化核物质的对称能, 但无损于基态性质与实验的一致性. 讨论了对称能的软化对巨单极共振的影响.     

双Λ超核同位旋标量巨共振性质的相对论研究

基于相对论平均场理论(RMF),采用TM1以及有效超子-核子和超子-超子相互作用,首先研究了¹⁶O和_ΛΛ¹⁸O的单粒子能级受超子的影响情况,发现超子的加入使得核子能级能量降低.其次基于相对论无规位相近似方法 (RRPA),自洽地计算了¹⁶O和_ΛΛ¹⁸O同位旋标量巨单极和四极共振态.发现相比于¹⁶O各巨共振的响应函数,超核的响应函数会发生改变.研究表明:这种改变主要来自于超子的加入导致的核子单粒子能级的改变,以及超子粒子-空穴组态跃迁的贡献,而超子-超子剩余相互作用对单极和四极共振在低能区的响应函数的影响比较小,特别对高能区的响应函数基本没有影响.     

巨共振激发的相对论效应

在相对论量子场论（ＱＨＤ）的框架下,得到了相对论线性Ｖｌａｓｏｖ方程．依此计算了球形核１６Ｏ、４０Ｃａ、９０Ｚｒ及２０８Ｐｂ的巨偶极共振的强度函数分布．结果表明,相对论效应是不可忽视的．计算得到的巨共振中心能量稍高于非相对论线性Ｖｌａｓｏｖ方程给出的对应值,与实验结果比较都有较好的符合．对计算结果作了简要的讨论,发现核子有效质量和平均场自旅轨道耦合力对巨共振能量有重要影想． In the framework of relativistic quantum hadron dynamical (QHD) theory,under semiclassical approximation and taking into vacuum fluctuation, a relativistic Vlasov equation (RVE) has been derived. Using RVE and considering other relativistic effects, we have studied the isovector dipole giant resonances built on ground state in spherical nuclei.The main results show that the resonance energies for each multipole are larger than those obtained from the non-relativistic classical Vlasov approach...     

格点核子-核子势在核物质中的相对论效应(英文)

利用最新的格点核子-核子势研究了核物质中的相对论效应。通过此格点核子-核子势场,首先我们构建一个包括π介子,σ介子以及ω介子的单玻色子交换势。势场中的介子-核子耦合常数以及截断动量通过拟合格点核力得到的核子-核子散射相移确定。随后采用非常成功的第一性原理多体计算方法Brueckner-Hartree-Fock模型,计算了核物质的基本性质。发现对称核物质的状态方程以及饱和性质在非相对论框架和相对论框架中有很明显的区别。在格点核力中,该相对论效应对核物质的结合能提供吸引的贡献。这与采用传统的核力计算得到的结果是相反的。The relativistic effect in nuclear matter is investigated with the latest lattice nucleon-nucleon (NN) potential. A one-boson-exchange potential (OBEP) including three mesons, pion, σ meson and ω meson was constructed based on the lattice NN potential. The meson-nucleon coupling constants and cutoff momentums are determined by fitting the phase shifts of NN scattering from lattice NN potential. The properties of nuclear matter with this OBEP from lattice potential are calculated by one very successful ab initio many-body method, Brueckner-Hartree-Fock model. The equations of state and saturation properties of symmetric nuclear matter present very obvious different behaviors in non-relativistic and relativistic frameworks. The relativistic effect plays attractive contributions with the components of S and D waves in lattice NN potential, which is opposite comparing to the relativistic effect from the conventional NN potential.     

Skyrme Hartree-Fock模型对中等质量超形变超核的研究（英文）

采用Skyrme Hartree-Fock 模型和微观的核子-超子相互作用对Ar 同位素和40Ca 及相应超核的超形变态进行了研究,计算结果表明,基态的Λ 超子分离能比激发态的大。这一结果与反对称化分子动力学模型的结果一致,而与相对论平均场的结果相反。这区别主要来源于不同模型中不同的相互作用导致的核心核及相应超核密度分布的不同。The superdeformed (SD) states in medium heavy hypernuclei with core nuclei of Ar isotopes and 40Ca are studied in the frame of Skyrme Hartree-Fock (SHF)+ BCS model together with a microscopic ΛN interaction. The calculation indicates that the Λ separation energy S_Λ of ground state is larger than that of SD state. The result is consistent with the antisymmetrized molecular dynamics (AMD) calculation, but inconsistent with that of relativistic mean field (RMF). The difference comes from the different interaction and density distribution in the core nuclei and the corresponding hypernuclei.     

RMF理论框架下用粒子数守恒方法处理对关联

在相对论平均场理论框架下,利用粒子数守恒方法处理对关联,给出了具体的理论公式和数值细节;并以24Ne为例,用该方法研究了它的基态和低激发态性质. Particle-number conserving method is adopted to treat the pairing correlations in the relativistic mean-field theory. The formalism and numerical techniques are presented. As an example, the ground state properties and low-lying excited states in~(24)Ne are studied.     

Sum Rule in a Consistent Relativistic Random-Phase Approximation

A fully consistent relativistic random-phase approximation (RRPA) is studied in the sense that the relativistic mean-field (RMF) wavefunction of nucleus and the particlehole residual interactions in the RRPA are calculated from the same effective Lagrangian. A consistent treatment of RRPA within the RMF approximation, i.e., no sea approximation, has to include also the pairs formed from the Dirac states and occupied Fermi states, which is essential for satisfying the current conservation. The inverse energy-weighted sum rule for the isoscalar giant monopole mode is investigated in the constrained RMF. It is found that the sum rule is fulfilled only in the case where the Dirac state contributions are included.     

Relativistic Mean-Field Approach to Infinite Nuclear Matter and Neutron Star

The properties of infinite nuclear matter and neutron star are studied theoretically in relativistic mean-field (RMF) approach with three typical parameter sets NL1, NL-SH and TM1. It is found that all these new RMF parameter sets can very satisfactorily reproduce the properties of high density matter. Among these parameter sets, TM1, with a nonlinear ω term, reproduces a slightly smaller energy, piessure and neutron star mass than NL-SH and NL1. The ρ meson field has a large influence on the properties of neutron star and infinite nuclear matter. A detailed discussion for the significance of numerical results is also given.     

Isovector Scalar Field Effects in Asymmetric Nuclear Matter

Density-dependent parametrization models of the nucleon-meson coupfing constants, including the isovector scalar δ-field, are applied to asymmetric nuclear matter. The nuclear equation of state （EOS） and the neutron star properties are studied in a relativistic Lagrangian density, using the relativistic mean field （RMF） hadron theory. It is known that the δ-field in the constant coupling scheme leads to a larger repulsion in dense neutron-rich matter and to a definite splitting of proton and neutron effective masses, finally influences the stability of the neutron stars. We use density-dependent models of the nucleon-meson couplings to study the properties of neutron star matter and to reexamine the （~-field effects in asymmetric nuclear matter. Our calculation shows that the stability conditions of the neutron star matter can be improved in presence of the δ-meson in the density-dependent models of the coupling constants. The EOS of nuclear matter strongly depends on the density dependence of the interactions.     

Relativistic Effective Interaction

In analogy with the idea of the effective interaction commonly used in the nonrelativistic approach, the relativistic effective .interactions are adopted to incorporate the relativistic Brueckner-Hartree-Fock (RBHF) results in the relativistic mean field approach (RMF) or relativistic Hartree-Fock approach (RHF). It is desired to remedy the deficiencies of RMF and RHF without losing the features of the relativistic G matrix and at the same time retain the simplicity. The relativistic effective interactions are used to describe the ground state properties of nuclei and medium-energy nucleon-nucleus scattering in this paper.     

Dynamics of nuclei with antikaons

Self-consistent calculations of single -nuclear states and multi -nuclear states are briefly reviewed. Dynamical effects for deeply bound nuclear states are studied within the relativistic mean-field (RMF) approach. By varying the strength of -nucleus interaction, we cover a wide range of binding energies . Our calculations provide a lower limit on the widths of nuclear bound states for binding energy in the range . Substantial polarization is found in light nuclei for deeply bound nuclear states, with central nuclear densities about twice higher than for the corresponding nuclei without . Multi- nuclear calculations indicate that the binding energy per meson saturates upon increasing the number of mesons embedded in the nuclear medium. The nuclear and densities increase only moderately and are close to saturation, with no indication of any kaon-condensation precursor phenomena.     

Nucleon momentum distribution of ~(56)Fe from the axially deformed relativistic mean-field model with nucleon-nucleon correlations

Nucleon momentum distribution(NMD), particularly its high-momentum components, is essential for understanding the nucleonnucleon(NN) correlations in nuclei. Herein, we develop the studies of NMD of ~(56)Fe from the axially deformed relativistic mean-field(RMF) model. Moreover, we introduce the effects of NN correlation into the RMF model from phenomenological models basing on deuteron and nuclear matter. For the region k k_F, the effects of deformation on the NMD of the RMF model are investigated using the total and single-particle NMDs. For the region k k_F, the high-momentum components of the RMF model are modified by the effects of NN correlation, which agree with the experimental data. Comparing the NMD of relativistic and non-relativistic mean-field models, the relativistic effects on nuclear structures in momentum space are analyzed. Finally, by analogizing the tensor correlations in deuteron and Jastrow-type correlations in nuclear matter, the behaviors and contributions of NN correlations in ~(56)Fe are further analyzed, which helps clarify the effects of the tensor force on the NMD of heavy nuclei.     

Structure of nuclei far from the stability in relativistic approach

The recent progress of the relativistic many-body approach by the group at Peking University will be reviewed. In particular, axially deformed relativistic Hartree-Bogoliubov approach in Woods-Saxon basis aiming at halo nucleus, time-odd triaxial RMF approach, the adiabatic and configuration-fixed constrained triaxial RMF approaches, a Reflection ASymmetric RMF (RAS-RMF) approach, and a new relativistic Hartree-Fock (RHF) approach with density-dependent σ,ω,ρ and π meson-nucleon couplings for finite nuclei and nuclear matter, will be highlighted.