N-N INTERACTION IN THE DEFORMED CHIRAL BAG I

Using the hybrid chiral bag a formulation is developed for discussing the short range behaviour of the nuclear force. Quarks interact with each other via exchange gluons inside the bag and exchange "pion field" quanta on the bag surface. In terms of the Green's functions for the confined quarks, gluons in the bag and pions outside the bag the second order perturbation interaction energy of the sixquark state is derived. In principle, it can be used for any configurations. To compare with the result without the pion field outside the bag the DeTar's six-quark states are used for the numerical calculation. As estimated, the streagth of the repulsion core will increase. The numerical result will be shown in the succeeding paper.     

CONTRIBUTIONS TO THE SHORT RANGE NUCLEAR FORCE FROPI THE QUARK-PION INTERACTION IN THE CHIRAL BAG MODEL

The contributions to the short range nuclear force from the quark-pion interaction in the Chiral Bag Model have been investigated.The antisymmetric wave functions for the physical channels of N-N, Δ-Δ and C-C are obtained in terms of the group classification and fractional parentage reduction. Assuming six quarks in a spherical bag, the separation of the quark triplets is described in terms of two orbitals-left and righ which are composed of the quark S and P states. The results show that the contribution to the short range nuclear force from one pion exchange of the quarks is repulsive about 150 MeV.     

The fuzzy bag and baryonic properties with center of mass and recoil corrections

The fuzzy bag is a hadronic model which has features both of the bag model (energy-momentum conservation, QCD vacuum energy) and of relativistic potential models (confinement achieved through a potential). It is also a chiral model, with the unique property that the pion field is suppressed in the interior of the bag by means of a scalar potential, and yet chiral symmetry is preserved. This scalar potential allows one to control how far the pion field can penetrate in the interior of the bag. We calculate the masses of the fundamental baryon octet taking into account the center of mass, one-gluon exchange and one-pion exchange corrections. We also calculate the nucleon axial charge, charge radii and magnetic moments including center of mass and recoil corrections. The agreement with experiment is excellent, and the results indicate that the pion field is suppressed only very close to the center of the bag. Received: 14 January 2003 / Published online: 5 May 2003 RID="a" ID="a" e-mail: pilotto@if.ufrgs.br     

THE VIRTUAL EXCHANGE OF PSEUDOSCALAR MESONS IN THE MIT BAG MODEL

In this paper the virtual exchange effect of pseudoscalar mesons in the MZT bag model is discussed and the mass spectrum of hadrons,the magnetic moment's and the mean square values of charge radius are calculated. It is pointed out that our model can pre-serve and improve the static properties of the MIT bag model and provide an explanation for the origin of the meson cloud outside.     

MASSES OF THE LIGHT HADRONS AND SELF-ENERGIES IN THE BAG MODEL

The masses of the light hadrons are calculated in terms. of the cloudy bag model with use of pion-energies due to both gluon and pion exchange. By use of a type of pion-guark interaction which incorporates the finite extent of the pion the convergent self-energy due to pion exchange is obtained. The difficulties in the bag models which only include one type of the self-energies can be removed by. taking account of both and the baryon spectrum is reproduced well. It is found that these self-energies are large but have opposite effect on the masses of the hadrons.     

Quark models of nuclear isobaric energy differences

We study the energy differences between mirror nuclei in both nonrelativistic (NR) and relativistic quark models based on the one-gluon exchange interaction. Both six-quark (6q) and resonating-group (RG) methods are used to treat the effects of overlapping nucleons in nuclei. The 6q method is simple and useful, but it can give only qualitative results because of a lack of precision and the neglect of non-(1s)⁶ configurations. It is used here to compare bag and potential models of quarks and to study the effects of kinetic energy, quark-quark interaction and nucleon size. Six-quark results show that the usual Breit-Fermi NR reduction has serious limitations in treating quark masses and nucleon sizes. In contrast, the RG method is much more complete, but it is also much harder to use. It is used here with simple NR potential models to study the effects of complicated 6q configurations, nucleon size and nucleon-nucleon short-range correlations. We find that NR potential models tend to give Nolan-Schiffer anomalies larger than experimental results, while bag models give too small results, especially if the bag radius is as small as 0.6 fm.     

Bag-model quantum chromodynamics for hyperons at low energy

In a non-perturbative bag model framework, gluon exchange which mediates quark exchange scattering in conjunction with quark interchange is shown to be the basis of the OBE interactions of hyperons at low energy.     

Zero-point motion in the bag description of the nucleon

In the bag model, confinement of quarks is accomplished by introduction of a boundary condition at some definite radius $\text{R}$, where the energy of the total system is a minimum. This minimum is, however, realtively shallow and energies for substantially different bag radii are not much larger than this minimum value. This indicates that the zero-point motion of the bag surface may be important.In this paper, quantization of the bag surface motion is carried out in a somewhat ad hoc fashion, modelled after the generator coordinate theory in nuclear physics. This procedure unifies a number of ideas previously in the literature; it stresses the anharmonicity of the collective motion. As in earlier treatments, the Roper resonance emerges as a breathing-mode type of excitation of the nucleon.The one- and two-pion decays of the Roper resonance are calculated and the widths are found to fall short of the empirical ones. It is pointed out, however, that decays involving intermediate states containing virtual ρ-mesons will enhance the widths. Pion-nucleon scattering in the P₁₁ channel is constructed in our model and found to agree roughly with experiment. A crucial term in the driving force involves the pion coupling to the nucleon through a virtual ρ-meson.With introduction of zero-point motion of the bag surface, the notion of “bag radius” becomes dependent on precisely which moment of the radius is measured. Our development gives a model for cutting off smoothly the pion-exchange term in the nucleon-nucleon interaction.     

Towards a Quantum Bag Dynamics (Ⅲ)-Collective Motion of the Bag

It is showed, that under the adiabatic assumption, the quark-gluon state and the energy of a dynamic bag may be expressed as functions of its collective coordinates and their first time derivatives. The effective-lagrangian and IIamiltonian for the collective motion arethen proposed. The classical equation of coJJective motion is suggested to be used as the self-consistent equation for the force function f(R, R). The bag dynanlics is once again quantized. A set of ellipsoids and their finite combinations is recommended as a complete set of bag shapes because of its Lorentz invariance. The wave function for tlle internal motion of a hadron is therefore a function of the bag shape configuration..It may be used to average intrinsic observables and matrix elements of a hadron over the shape configuration. The zero momentum eigenstate of a hadron is constructed by making use of its translational symmetry. Finite momentum eigenstates are then constructed by Lorentz boosts. Multi-hadron states and hadron interactions are also considered.     

SHORT RANGE N-N INTERACTION IN THE CHIRAL BAG MODEL

Using the chiral bag model a quark theory of N-N interaction is formulated. In terms of the Green's functions of quark, gluon and Goldstone boson('pion')fields in the model,the effective nuclear potentials have been calculated for the different (TS) channels.There is a repulsive core in the potentials.The strength is about several hundreds MeV.About one fourth of the repulsion is due to 'pion' exchange.     

The influence of electron exchange and relativistic corrections on elastic low energy electron diffraction from compound semiconductors

The model of the electron-solid interaction used for dynamical low energy electron diffraction (LEED) calculations is extended to include both an energy dependent local exchange interaction and relativistically computed ion-core charge densities. These extensions of earlier work based on non-relativistic, local exchange models are tested for the (110) surfaces of InP, ZnTe and InSb. Calculations reveal discernible differences between LEED intensities computed using the energy dependent exchange force and those obtained using energy independent local exchange forces. The replacement of the non-relativistic ion-core potential with a relativistic one produces smaller changes which are most apparent when the energy dependent exchange force is used for compound semiconductors containing one or more components from the fifth row or lower in the periodic table (e.g., Cd, In, Sb or Te).     

Arguments against one-boson-exchange models of nuclear forces and new mechanism for intermediate-and short-range nucleon-nucleon interaction

Arguments against the traditional Yukawa-type approach to NN intermediate-and shortrange interaction due to scalar-isoscalar and heavy-meson exchanges are presented. Instead of the Yukawa mechanism for intermediate-range attraction, some new approach based on the formation of a symmetric six-quark bag in the state |(0s)⁶[6]_X, L=0〉 dressed owing to strong coupling to π, σ, and ρ fields is suggested. This new mechanism offers a strong intermediate-range attraction, which replaces effective σ exchange (or excitation of two isobars in the intermediate state) in traditional force models. A similar mechanism with the production of a vector ρ meson in the intermediate six-quark state is expected to lead to a strong short-range spin-orbit nonlocal interaction in the NN system, which may resolve the long-standing puzzle of the spin-orbit force in baryons and in two-baryon systems. The effective interaction in the NN channel provided by the new mechanism will be enhanced significantly if the partial restoration of chiral symmetry is assumed to occur inside the six-quark symmetric bag. A simple illustrative model is developed that demonstrates clearly how well the suggested new mechanism can reproduce NN data. Strong interrelations have been shown to exist between the proposed microscopic model and one-component Moscow NN potential developed by the authors previously and also with some hybrid models and the one-term separable Tabakin potential. The new implications of the proposed model for nuclear physics are discussed.     

One-gluon exchange corrections to magnetic moments of baryons

One-gluon exchange (OGE) corrections to the magnetic moments of the octet baryons are studied in the bag model. It is clarified that OGE resolves a problem of μ(Λ) and μ(Ξ^?) in previous quark model calculations and also improves an overall agreement between theory and experiment.     

A compressible bag model and equation of state for high density nuclear matter

We propose a compressible bag model, in which a nucleon bag responds microscopic thermal pressure of the other bags. The volume exclusion effect and the particle exchange type interaction ensure the saturation property of the nucleus at normal density and bring about the deconfinement transition in high density region. The critical values of chemical potential and baryon number density for nuclear/neutron matter are estimated. Our equation of state is applied to neutron stars, and shown to be consistent with the observed rotation periods of millisecond pulsars.     

Possibility of measuring exchange force through force microscopy

This article describes the possibility of measuring exchange force through atomic force microscopy (AFM), based on the results of first-principles calculations for the exchange force between two magnetic Fe(001) films. We observed strong variation of the exchange force relative to the surface site. The magnitude of the force variation was larger than the force sensitivity of conventional AFM. These results suggest that a surface magnetic image with atomic resolution can be achieved by measuring the exchange force.     

核力介子交换理论的新进展

本文评述了核力介子交换理论的研究进展,内容包括相对论单玻色交换势,核力介子交换的非协变微扰理论,能量无关N-N介子交换势和巴黎势的一些最新进展。     

铁磁共振磁交换力显微镜

原子间的自旋相互作用力对原子级别磁性纳米构造体的表面磁性质的理解是极为重要的. 磁交换力显微镜是测量表面自旋作用力的重要手段, 但它的缺点一是需要加外部强磁场, 二是不能分离表面形貌和自旋信息, 这就导致材料表面受外部磁场的影响, 而且表面形貌和自旋信息之间相互影响, 使自旋间的相互作用力的检测和成像研究受到限制.为了解决上述问题, 利用原子力显微镜, 并采用微波照射的方法, 根据铁磁共振原理, 分别独立提取磁性材料表面形貌和自旋信息, 称之为铁磁共振磁交换力显微镜, 理论和实验结果表明此方法可以有效地分离两种信息. 铁磁共振磁交换力显微镜可以促进对原子级磁性材料机能的理解以及磁性相关科学领域的进步, 特别是对自旋电子元件的发展有很大的促进作用, 是新世纪高度信息化社会不可缺少的测量技术. 关键词： 原子力显微镜 磁交换力显微镜 自旋 铁磁共振     

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 deuteron asymptotic D-state as a probe of the nucleon-nucleon force

A critical discussion is given of the various contributions to the asymptotic D/S ratio from the πNN interaction. Particular emphasis is laid on the analysis of contributions from 2π exchange, the dependence on the πNN form factor, and on the πN coupling constant, so as to assess quantitatively the model dependence of the result. From this analysis, significant restrictions are deduced on the shape of the πNN form factor and, in quark bag models, the value of the quark bag radius. The results of previous theoretical approaches for the D/S ratio and quadrupole moment are shown to obey a universal and linear relation, when expressed in reduced units so as to compensate for small differences in effective range and πN coupling constant. The quadrupole moment is also quantitatively analyzed in detail. Its value is proved to be an accurate and almost model-independent consequence of the experimental D/S ratio (apart from relativistic and meson-exchange corrections) in agreement with observations. In the comparison with experiments, a critical survey of the relevant experimental data is given. In particular, a considerably improved value for the quadrupole moment is deduced.