Baryon-baryon spin-orbit and tensor interactions from quark-exchange kernels

Dibaryon quark-exchange kernels are constructed in explicit analytic form for the tensor and spin-orbit terms of the one-gluon-exchange quark-quark Breit interaction and for spin-orbit terms generated by quark-confinement mechanisms. The spin operators needed are defined through their spin-reduced matrix elements including those needed for interactions coupling NN, NΔ, and ΔΔ channels. Effective baryon-baryon spin-orbit potentials, generated through the Wigner transforms of the quark-exchange kernels with the use of a local momentum approximation, show that the NN spin-orbit interaction derived from the symmetric spin-orbit term of the one-gluon-exchange quark-quark interaction is in general agreement with the short-range part of phenomenological potentials derived from NN scattering. With the inclusion of the antisymmetric spin-orbit one-gluon-exchange terms and spin-orbit terms generated by confining potentials the full triplet-odd NN spin-orbit potential is greatly reduced in the 0.5–1 fm range. The uncertainties associated with spin-orbit terms generated by quark-confinement mechanisms are emphasized. The relative importance of various possible quark-gluon exchange terms is studied and shows that models which neglect some types of exchange terms are open to question. An SU(3)-flavor symmetric model for N-hyperon spin-orbit potentials leads to an NΛ spin-orbit potential only slightly weaker than the NN spin-orbit potential.     

Influence of six-quark bags on the NN interaction in a resonating group scattering calculation

The influence of six-quark bags on the nucleon-nucleon (NN) interaction is studied in a dynamical calculation of the NN scattering process. The NN interaction is described by the exchange of gluons and pions between quarks and a phenomenological σ-meson exchange between nucleons. The quark wave functions are harmonic oscillators and the relative wave function between the two nucleons is determined by the resonating group method. At short distances the NN system is allowed to fuse to a six-quark bag where all six quarks are in a ground state or where two quarks are in excited Op states. The sizes of these six-quark bags are dynamical parameters in the resonating group calculation allowing for spatial polarisation effects during the interaction. The S-wave NN scattering data can be reproduced by adjusting the σ-coupling strength. The main result is that the six-quark bags with an increased radius have a large influence on the NN scattering process.     

The Skyrmion Skyrmion interaction and the meson exchange model for the NN potential

The properties of nucleon-nucleon (NN) potentials derived from the Skyrme model are investigated compared to those of typical One-Boson-Exchange (OBE) models, For that purpose the NN as well as the nucleon-antinucleon (N¯N) potentials are evaluated for the isoscalar central channel, the isovector spin channel, and the isovector tensor channel. A comparison of NN and N¯N interactions allows a separation into terms with positive and negativeG-parity and therefore a detailed comparison with the properties of the OBE model. This analysis is performed using the classical Lagrangian of the Skyrme model and considering an extension of this Lagrangian by a term of sixth order, which has recently been proposed. The results indicate that the extended Lagrangian yields an interaction which is quite consistent with the OBE picture. The extended model, however, is much more sensitive to the values of the parameters and the approximations being used for the evaluation of the field for two baryons.     

Spin-Orbit Force of NN Interaction Based on Chiral SU(3) Quark Model

Spin-orbit force of the NN interaction is studied in the framework of the chiral SU(3) quark model. Both symmetric and antisymmetric spin-orbit (LS) forces of the one gluon exchange and scalar meson exchanges are taken into account. It is shown that although the inclusions of the LS forces caused by the scalar meson exchanges and the antisymmetric LS terms in this model can notably strengthen the LS couplings in the states of ³P_J of the NN interaction, an additional enhancement factor is still needed in order to describe the experimental data.     

Nucleon--nucleon interactions in the double folding model for fusion reactions

Nucleus--nucleus potentials are determined in the framework of double folding model for M3Y--Reid and M3Y--Paris effective nucleon--nucleon (NN) interactions. Both zero-range and finite-range exchange parts of NN interactions are considered in the folding procedure. In this paper the spherical projectile--spherical target system ¹⁶O+²⁰⁸Pb is selected for calculating the barrier energies, fusion cross sections and barrier distributions with the density-independent and density-dependent NN interactions on the basis of M3Y--Reid and M3Y--Paris NN interactions. The barrier energies become lower for Paris NN interactions in comparison with Reid NN interactions, and also for finite-range exchange part in comparison with zero-range exchange part. The density-dependent NN interactions give similar fusion cross sections and barrier distributions, and the density-independent NN interaction causes the barrier distribution moving to a higher position. However, the density-independent Reid NN interaction with zero-range exchange part gives the lowest fusion cross sections. We find that the calculated fusion cross sections and the barrier distributions are in agreement with the experimental data after renormalization of the nuclear potential due to coupled-channel effect.     

The three-nucleon problems with weak NN interaction

We consider the three-nucleon system in which each two-nucleon pair interacts both strongly and weakly. The strong part is assumed to be separable but an addition of small non-separable term is possible. The weak two-nucleon interaction (which is absolutely non-separable) is assumed to be given in terms of its partial wave components in momentum space. These elements have been calculated by Lassey and McKellar starting from recent models of non-relativistic (strangeness conserving non-leotonic) NN weak interaction. An expression for the weak part of the elastic nucleon-deuteron scattering amplitude is derived within the framework of two potential scattering theory. The weak three-body driving terms are explicitly evaluated. They reflect weak form factors responsible for the weak dissociation of two nucleon isobars (including parity impurity of the deuteron wave function) as well as weak NN scattering. The expressions appearing below are numerically tractable and can be used to elaborate on previous calculations.     

Correlations and the Dirac structure of the nucleon self-energy

The Dirac structure of the nucleon self-energy in symmetric nuclear matter as well as neutron matter is derived from a realistic meson exchange model for the nucleon-nucleon (NN) interaction. It is demonstrated that the effects of correlations on the effective NN interaction in the nuclear medium can be parameterized by means of an effective meson exchange. This analysis leads to a very intuitive interpretation of correlation effects and also provides an efficient parametrization of an effective interaction to be used in relativistic structure calculations for finite nuclei. Received: 29 January 2001 / Accepted: 5 May 2001     

双折叠模型对相互作用势实部的计算

用双折叠模型计算了核核碰撞的相互作用势, 其中核子-核子相互作用势采用M3Y-Reid和M3Y-Paris形式, 交换部分考虑了有限力程的密度依赖的核子-核子相互作用, 程序用于重离子散射光学势实部的计算. 回顾了折叠模型的普遍特征和讨论了理论计算过程, 对各种类型的核子-核子相互作用下计算的相互作用势进行比较, 发现双折叠模型对大部分系统相互作用势的实部取得了满意的结果. 因此这个工作为重离子相互作用势的折叠计算提供了很好的方法.     

扩展Su-Schrieffer-Heeger模型在周期性边界条件下的相变

文章计算了含有三种跃迁项(最近邻(NN)、次近邻(NNN)、次次近邻(NNNN)跃迁项)的扩展Su-Schrieffer-Heeger(SSH)模型(模型ⅰ)的热力学特性.对仅含有二种跃迁项(NN、NNN跃迁项)的扩展SSH模型(模型ⅱ)、仅含有一种跃迁项(NN跃迁项)的SSH模型(模型ⅲ)也作了类似的计算.在低温下,每个模型都有相变且跃迁项的存在会降低相变温度.由于NNN跃迁项的存在,在极低温条件下,关于热容量与温度比(HCOTR)随温度变化的单调性,模型i与其它两个模型存在差异.在低温下,模型ⅰ的HCOTR的单调性,会受NN或NNN或NNNN跃迁项的影响并且NN或NNN跃迁项会影响其相变.     

A Separable Pairing Force in Nuclear Matter

The method introduced by Duguet is adopted to derive a separable form of the pairing interaction in the ^1So channel from a bare or an effective nucleon-nucleon （NN） interaction in nuclear matter. With this approach the separable pairing interaction reproduces the pairing properties provided by its corresponding NN interaction. In this work, separable forms of pairing interactions in the ^1So channel for the bare NN interaction, Bonn potential and the Gogny effective interaction are obtained. It is found that the separable force of the Gogny effective interaction in the 1So channel has a clear link with the bare NN interaction. With such a simple separable form pairing properties provided by the Gogny force in nuclear matter can be reproduced.     

Phenomenology of the nucleon-nucleon potential

A local nucleon-nucleon potential expansion is developed in terms of orthogonal projectors. Considering the nucleon-nucleon (NN) potential as a completely phenomenological structure, the expansion provides an opportunity to obtain the NN scattering phase shifts that can be described by applying a restricted set of operators, dependent on angular and spin-isospin degrees of freedom of the interacting nucleons. The results obtained with an approximation for eight basic operators (central, spin-orbit and tensorial) are consistent with experience in the field, and provide directions for further modifications of realistic NN potentials.     

Local forces and the 16O reaction matrix

It is demonstrated that the G-matrix elements obtained from a solution of the Bethe-Goldstone equation for finite nuclei and a given NN interaction can be very well approximated by an effective local interaction. The local approximation is determined from the reaction matrix in nuclear matter using the same realistic NN interaction. The comparison is performed on the level of RPA calculations for the excited states in ¹⁶O. Very good agreement is found between the results for both interactions except for scalar-isoscalar states. It is shown that this is due to the energy dependence of the reaction matrix and can be cured rather easily. A comparison with experiment for isovector states is very satisfactory.     

Short range behaviour of the N-N potential within the quark Model

The short range behaviour of the nucleon-nucleon (NN) potential is studied in terms of the quark model, where nucleons are assumed to consist of three colored quarks. By considering the overlap kernel of the wave function of the resonating group method (RGM), it is found that the Pauli effect does not produce a ‘hard core’. Instead, the gluon exchange interaction with the confinement requirement suggests a rather soft one. TheΔ-Δ isobar interaction is also considered. In the (S, T) = (3, 3), (3, 2) and (2, 3) channels we find a ‘hard core’, while calculations in some other cases indicate even strong short range attractions.     

Probing the medium effect and isospin dependence of the in-medium nucleon--nucleon cross section in heavy ion collisions

Probing in-medium nucleon-nucleon （NN） cross section σ1/NN（α） in heavy ion collisions has been investigated by means of the isospin-dependent quantum molecular dynamics （IQMD） with the isospin- and momentum-dependent interaction （IMDI（T））. It is found that there are the very obvious medium effect and the sensitive isospin-dependence of nuclear stopping R on the in-medium NN cross section α1/NN（α） in the nuclear reactions induced by halo-neutron projectile and the same-mass stable projectile. However, R induced by the neutron-halo projectile is obviously lower than that induced by the corresponding stable projectile. In particular, there is a very obvious dependence of R on the medium effect of σ1/NN（α） in the whole beam energy region for the above two kinds of projectiles. Therefore, the comparison between the results of R＇s in the reactions induced by the neutron-halo projectile and the corresponding same-mass stable projectile is a more favourable probe for extracting the information of σ1/NN（α） because of adding a new judgement.[第一段]     

Comparing some nucleon-nucleon potentials

The aim is to compare a few Nucleon-Nucleon (NN) potentials especially Reid68, Reid68-Day, Reid93, UrbanaV14, ArgonneV18, Nijmegen 93, Nijmegen I and Nijmegen II. Although these potentials have some likenesses and are almost phenomenological, they include in general different structures and their own characteristics. The potentials are constructed in a manner that fit NN scattering data or phase shifts and are compared in this way. A high-quality scale of a potential is that it fits the data with χ²/N _data ≈ 1, describes well the deuteron properties and gives satisfactory results in nuclear-structure calculations. However, these scales have some failures. Here, we first compare many potentials by confronting them with the data. Then, we try to compare the potential forms by considering the potential structures directly and therefore regarding their substantial bases somehow. To do so, we note that since the potentials are written in different schemas, it is necessary to write them in a unique schema. On the other hand, because three major terms in the NN interaction are central, tensor and spin-orbit terms; so, to perform a reduction plan and arrive at a common structure, we choose the Reid’s potential form. Next, we compare the potentials for some states and address some other related issues as well.     

Properties of 12C in the Ab initio nuclear shell model

We obtain properties of 12C in the ab initio no-core nuclear shell model. The effective Hamiltonians are derived microscopically from the realistic CD Bonn and the Argonne V8' nucleon-nucleon (NN) potentials as a function of the finite harmonic oscillator basis space. Binding energies, excitation spectra, and electromagnetic properties are presented for model spaces up to 5Planck's over 2piOmega. The favorable comparison with available data is a consequence of the underlying NN interaction rather than a phenomenological fit.