Quarks in the NN interaction

This talk summarizes the results obtained by the Paris group during the last few years on the effects of quark degrees of freedom in the NN interaction.     

The role of meson retardation in the NN interaction above pion threshold

A model is developed for the hadronic interaction in the two-nucleon system above pion threshold which is based on meson, nucleon and Δ degrees of freedom and which includes full meson retardation in the exchange operators. For technical reasons, the model allows maximal one meson to be present explicitly. Thus the Hilbert space contains besides NN and NΔ also configurations consisting of two nucleons and one meson. For this reason, only two- and three-body unitarity is obeyed, and the model is suited for reactions in the two-nucleon sector, where only one pion is produced or absorbed. Starting from a realistic pure nucleonic retarded potential, which had to be renormalized because of the additional π and Δ degrees of freedom, a reasonable fit to experimental NN-scattering data could be achieved.     

Four-body calculation of ΛH and ΛHe with realistic YN and NN interactions

We carried out four-body calculations of _Λ⁴H and _Λ⁴He taking both the 3N + Λ and 3N + Σ channels explicity with the use of realistic NN and YN interactions. The Σ-channel component plays an important role in binding energies of the A = 4 hypernuclei though the admixture is approximately 1%. The ΛN - ΣN coupling is found to be of central-force type in the Nijmegen model D and of tensor-force type in the model F.     

The NN → NNη reaction close to threshold

The pp → ppη and np → npη reactions at energies near the η production threshold are studied in a non-relativistic one boson exchange model, where the N^* (1535 MeV) S11 resonance is excited through the exchange of π, η, and ω mesons and subsequently decays into an ηN pair. Energy integrated cross sections and energy spectra of the out going η's are reported. Providing NN and ηN final state interactions are taken into account coherently, the model reproduces both the scale and energy dependence of the cross section for the pp → ppη reactions up to 100 MeV. Final state interaction corrections due to the nucleon-nucleon and meson-nucleon forces influence strongly the scale and shape of the cross sections. The shape of the energy spectra of the outgoing η's provides a clear signature of the ηN force.     

Pion mass effects on axion emission from neutron stars through NN bremsstrahlung processes

The rates of axion emission by nucleon–nucleon bremsstrahlung are calculated with the inclusion of the full momentum contribution from a nuclear one pion exchange (OPE) potential. The contributions of the neutron–neutron (nn), proton–proton ( pp) and neutron–proton (np) processes in both the non-degenerate and degenerate limits are explicitly given. We find that the finite-momentum corrections to the emissivities are quantitatively significant for the non-degenerate regime and temperature-dependent, and should affect the existing axion mass bounds. The trend of these nuclear effects is to diminish the emissivities.     

Level spectra of Ni-isotopes with realistic interaction

Quasiparticle configuration-mixing calculations are made for the Ni-isotopes with an approximate reaction matrix of Hamada-Johnston potential reported by Kuo. The results are very close to those obtained by the exact shell-model calculations. But the agreement with the experimental spectra is poor in both these cases. A remarkable improvement is achieved in the quasiparticle results when the renormalized force strength and the quasiparticle quantities extracted by the inverse gap equation procedure are used. A possible further improvement in the inverse gap equation procedure is discussed.     

The projected Hartree-Fock spectra from a realistic two-body interaction

The projection method is used to obtain good angular momentum and good isospin states from the intrinsic Hartree-Fock states of the nuclei in the 2s-1d shell. An effective interaction derived from the Yale potential has been employed in the calculations. It is found that the static magnetic moments are predicted correctly. The static quadrupole moments and the lifetimes of the nuclear states for electric quadrupole transitions are predicted correctly if an effective charge of 0.5 e is ascribed to the neutrons. The projected energy spectra in even-mass nuclei are very much compressed as compared to the experimental spectra. The agreement between the projected and the experimental spectra in odd-mass nuclei is not so bad.     

Vortical gust boundary condition for realistic rotor wake/stator interaction noise prediction using computational aeroacoustics

In this work, the NASA Glenn Research Center Broadband Aeroacoustic Stator Simulation (BASS) code is extended for use in the prediction of noise produced by realistic three-dimensional rotor wakes impinging on a downstream stator row. In order to accurately simulate such a flow using a nonlinear time-accurate solver, the inflow and outflow boundary conditions must simultaneously maintain the desired mean flow, allow outgoing vortical, entropic, and acoustic waves to cleanly exit the domain, and accurately impose the desired incoming flow disturbances. This work validates a new method for the acoustics-free imposition of three-dimensional vortical disturbances using benchmark test cases.     

Spin-other-orbit interaction in highly excited configurations with p and g electrons in outer shells

The matrix of the operator of the spin-other-orbit interaction energy is constructed for npn’g and np ⁵ n’g configurations. The matrix elements of this operator are calculated in the single-configuration approximation with wave functions in the LSJM representation and in the representation of uncoupled angular momenta using the known general formulas. The spin-other-orbit interaction is represented by three direct and three exchange radial Marvin spin interaction integrals.     

A realistic complex interaction for elastic and inelastic nucleon scattering

A parameter-free microscopic calculation for the elastic and inelastic scattering of protons is presented using a complex nuclear matter t-matrix interaction which was generated from the Hamada-Johnston internucleon potential. The transitions ²⁷Al(p,n) and ⁴⁰Ca(p,p') are analyzed.     

Resonant acousto-optical interaction under realistic conditions of a broadened absorption line

A theory of the resonant acousto-optical interaction has been constructed for spectral line broadening of arbitrary character. Account is taken of the strongest of the mechanisms of resonant photoelasticity, associated with the potential-deformation interaction of light and sound. It is shown that when inhomogeneous broadening is present the maximum efficiency of the acoustooptical interaction over the optical absorption length is not not reached at exact resonance, as in the case of homogeneously broadened lines, but at some separation from it, at a distance of about the half-width of the absorption line. It is shown that a combined study of the diffraction efficiency of the acousto-optical interaction and the optical absorption coefficient at near-resonant frequencies would make it possible to obtain information on the contributions of homogeneous and inhomogeneous broadening in a real resonance and thus assess the quality of the material. Fiz. Tverd. Tela (St. Petersburg) 39, 1354–1357 (August 1997)     

Magnetism of fcc/fcc, hcp/hcp twin and fcc/hcp twin-like boundaries in cobalt

The magnetic moments of the fcc/fcc, hcp/hcp twin and fcc/hcp twin-like boundaries in cobalt were investigated by first-principles calculations based on density functional theory. The magnetic moments in fcc/fcc were larger than those of the bulk fcc, while the variations in the magnetic moment were complicated in hcp/hcp and fcc/hcp. The magnetovolume effect on the magnetic moment at the twin(-like) boundaries was investigated in terms of the local average atomic distance and the average deviation from equilibrium; however, the complicated variations in the magnetic moment could not be explained from the magnetovolume effect. Next, the narrowing (or broadening) of the partial density of states (PDOS) width of 3d orbitals, the number of occupied states for the spin-down channel, and the PDOS around the Fermi level were investigated. The entire variation in the magnetic moment at the twin(-like) boundaries could be understood in terms of these factors. Charge transfer occurred in hcp/hcp. In this case, the contributions of 4s and 4p electrons to the variation in the magnetic moment were relatively large.     

A many-body calculation of the hyperfine interaction in the lowest2S and2P states of li-like systems

A non-relativistic perturbation method of Brueckner-Goldstone type is used to calculate the hyperfine interactions in the lowest² S and² P states of the Li-like systems, Li, Be⁺, B²⁺, C³⁺, N⁴⁺, O⁵⁺ and F⁶⁺. The effect of the polarization of the closed shell is treated to all orders of perturbation, while the correlation effect is calculated in the lowest order, i.e. in the third order of the perturbation expansion. Experimental data are at present available only for Li, Be⁺ and F⁶⁺, and the agreement with the calculated values is in these cases very good, usually within the experimental uncertainties. This implies that the predictions made in the remaining cases should be quite reliable, which may simplify the experimental determination of these quantities. Theoretical values are also given for the quadrupole interaction, which can be used to determine the nuclear quadrupole moments, when accurate experimental information becomes available.     

Electromagnetic gyrokinetic δf particle-in-cell turbulence simulation with realistic equilibrium profiles and geometry

The δf particle-in-cell method for gyrokinetic simulations with kinetic electrons and electromagnetic perturbations [Y. Chen, S. Parker, J. Comput. Phys. 189 (2003) 463] is extended to include arbitrary toroidal equilibrium profiles and flux-surface shapes. The domain is an arbitrarily sized toroidal slice with periodicity assumed in toroidal direction. It is global radially and poloidally along the magnetic field. The differential operators and Jacobians are represented numerically which is a quite general approach with wide applicability. Discretization of the field equations is described. The issue of domain decomposition and particle load balancing is addressed. A derivation of the split-weight scheme is given, and numerical observations are given as to what algorithmic change leads to stable algorithm. It is shown that in the final split-weight algorithm the equation for the rate of change of the electric potential is solved in a way that is incompatible with the quasi-neutrality condition on the grid scale. This incompatibility, while negligible on the scale of interest, leads to better numerical stability on the grid scale. Some examples of linear simulations are presented to show the effects of flux-surface shaping on the linear mode growth rates. The issue of long-term weight growth in δf simulation and the effect of discrete particle noise are briefly discussed.     

The volume contribution of the ion-ion optical potential from realistic complex nucleon-nucleon interaction

The real and imaginary parts of the optical model potential for several pairs of magic nuclei have been calculated by a double folding procedure. The complex effective interaction is calculated from the Reid soft core potential by solving the Bethe-Goldstone equation in two colliding nuclear matters. The calculated potentials were approximated with a Woods-Saxon shape. We studied the dependence of the parameters of these Woods-Saxon forms on the masses of the interacting nuclei.     

Final-state hyperon-nucleon interaction in the inclusive K photoproduction from the deuteron

We calculate d(γ, K⁺) inclusive cross sections with the full inclusion of the final ΛN - ΣN interaction. Modern hyperon-nucleon forces and a recently updated production operator for the γ + N → K⁺ + Y process are used. Significant effects of the hyperon-nucleon final-state interaction have been found especially around the K⁺ΣN threshold.