264 research outputs found

    Correlations derived from Modern Nucleon-Nucleon Potentials

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    Various modern nucleon-nucleon (NN) potentials yield a very accurate fit to the nucleon-nucleon scattering phase shifts. The differences between these interactions in describing properties of nuclear matter are investigated. Various contributions to the total energy are evaluated employing the Hellmann - Feynman theorem. Special attention is paid to the two-nucleon correlation functions derived from these interactions. Differences in the predictions of the various interactions can be traced back to the inclusion of non-local terms.Comment: 7 pages, 4 figures include

    ΔI=1\Delta I=1 axial-vector mixing and charge symmetry breaking

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    Phenomenological Lagrangians that exhibit (broken) chiral symmetry as well as isospin violation suggest short-range charge symmetry breaking (CSB) nucleon-nucleon potentials with a \mbox{\boldmath \sigma}_1 \!\cdot\!\mbox{\boldmath \sigma}_2 structure. This structure could be realized by the mixing of axial-vector (1+1^+) mesons in a single-meson exchange picture. The Coleman-Glashow scheme for ΔIz=1\Delta I_{z}=1 charge symmetry breaking applied to meson and baryon SU(2)SU(2) mass splittings suggests a universal scale. This scale can be extended to ΔI=1\Delta I=1 nonstrange CSB transitions a1Hemf1\langle a_1^\circ|H_{em}|f_1\rangle of size 0.005-0.005 GeV2^2. The resulting nucleon-nucleon axial-vector meson exchange CSB potential then predicts ΔI=1\Delta I=1 effects which are small.Comment: 14 pages. To appear in Phys. Lett.

    Strange nuclear matter within Brueckner-Hartree-Fock Theory

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    We have developed a formalism for microscopic Brueckner-type calculations of dense nuclear matter that includes all types of baryon-baryon interactions and allows to treat any asymmetry on the fractions of the different species (n, p, Λ\Lambda, Σ0\Sigma^0, Σ+\Sigma^+, Σ\Sigma^-, Ξ\Xi^- and Ξ0\Xi^0). We present results for the different single-particle potentials focussing on situations that can be relevant in future microscopic studies of beta-stable neutron star matter with strangeness. We find the both the hyperon-nucleon and hyperon-hyperon interactions play a non-negligible role in determining the chemical potentials of the different species.Comment: 36 pages, LateX, includes 8 PostScript figures, (submitted to PRC

    Comment on Neutron-Proton Spin-Correlation Parameter A_{ZZ} at 68 Mev

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    We present two arguments indicating that the large value for the ϵ1\epsilon_1 mixing parameter at 50 MeV, which the Basel group extracted from their recent AzzA_{zz} measurement, may be incorrect. First, there are nucleon-nucleon (NN) potentials which predict the ϵ1\epsilon_1 at 50 MeV substantially below the Basel value and reproduce the Basel AzzA_{zz} data accurately. Second, the large value for ϵ1\epsilon_1 at 50 MeV proposed by the Basel group can only be explained by a model for the NN interaction which is very unrealistic (no ρ\rho-meson and essentially a point-like πNN\pi NN vertex) and overpredicts the ϵ1\epsilon_1 in the energy range where it is well determined (150--500 MeV) by a factor of two.Comment: 6 pages text (LaTex) and 2 figures (paper, will be faxed upon request), UI-NTH-930

    Can the magnetic moment contribution explain the A_y puzzle?

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    We evaluate the full one-photon-exchange Born amplitude for NdNd scattering. We include the contributions due to the magnetic moment of the proton or neutron, and the magnetic moment and quadrupole moment of the deuteron. It is found that the inclusion of the magnetic-moment interaction in the theoretical description of the NdNd scattering observables cannot resolve the long-standing AyA_y puzzle.Comment: 7 pages, 2 Postscript figures; to appear in Phys.Rev.

    Analysis of NN Amplitudes up to 2.5 GeV: An Optical Model and Geometric Interpretation

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    We analyse the SM97 partial wave amplitudes for nucleon--nucleon (NN) scattering to 2.5 GeV, in which resonance and meson production effects are evident for energies above pion production threshold. Our analyses are based upon boson exchange or quantum inversion potentials with which the sub-threshold data are fit perfectly. Above 300 MeV they are extrapolations, to which complex short ranged Gaussian potentials are added in the spirit of the optical models of nuclear physics and of diffraction models of high energy physics. The data to 2.5 GeV are all well fit. The energy dependences of these Gaussians are very smooth save for precise effects caused by the known Δ\Delta and N^\star resonances. With this approach, we confirm that the geometrical implications of the profile function found from diffraction scattering are pertinent in the regime 300 MeV to 2.5 GeV and that the overwhelming part of meson production comes from the QCD sector of the nucleons when they have a separation of their centres of 1 to 1.2 fm. This analysis shows that the elastic NN scattering data above 300 MeV can be understood with a local potential operator as well as has the data below 300 MeV.Comment: 49 pages, including 23 figures, LaTeX2e/RevTeX/ps fil

    Comment on piNN Coupling from High Precision np Charge Exchange at 162 MeV

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    In this updated and expanded version of our delayed Comment we show that the np backward cross section, as presented by the Uppsala group, is seriously flawed (more than 25 sd.). The main reason is the incorrect normalization of the data. We show also that their extrapolation method, used to determine the charged piNN coupling constant, is a factor of about 10 less accurate than claimed by Ericson et al. The large extrapolation error makes the determination of the coupling constant by the Uppsala group totally uninteresting.Comment: 5 pages, latex2e with a4wide.sty. This is an updated and extended version of the Comment published in Phys. Rev. Letters 81, 5253 (1998
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