221 research outputs found
axial-vector mixing and charge symmetry breaking
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 () mesons in a single-meson
exchange picture. The Coleman-Glashow scheme for charge
symmetry breaking applied to meson and baryon mass splittings suggests
a universal scale. This scale can be extended to nonstrange CSB
transitions of size GeV. The
resulting nucleon-nucleon axial-vector meson exchange CSB potential then
predicts effects which are small.Comment: 14 pages. To appear in Phys. Lett.
Strange nuclear matter within Brueckner-Hartree-Fock Theory
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,
, , , , and ). 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
We present two arguments indicating that the large value for the
mixing parameter at 50 MeV, which the Basel group extracted from their recent
measurement, may be incorrect. First, there are nucleon-nucleon (NN)
potentials which predict the at 50 MeV substantially below the
Basel value and reproduce the Basel data accurately. Second, the large
value for at 50 MeV proposed by the Basel group can only be
explained by a model for the NN interaction which is very unrealistic (no
-meson and essentially a point-like vertex) and overpredicts the
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?
We evaluate the full one-photon-exchange Born amplitude for 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 scattering observables cannot resolve the long-standing
puzzle.Comment: 7 pages, 2 Postscript figures; to appear in Phys.Rev.
Nucleon-Nucleon Phase Shifts and Pairing in Neutron Matter and Nuclear Matter
We consider 1S0 pairing in infinite neutron matter and nuclear matter and
show that in the lowest order approximation, where the pairing interaction is
taken to be the bare nucleon-nucleon (NN) interaction in the 1S0 channel, the
pairing interaction and the energy gap can be determined directly from the 1S0
phase shifts. This is due to the almost separable character of the NN
interaction in this partial wave. Since the most recent NN interactions are
charge-dependent, we have to solve coupled gap equations for proton-proton,
neutron-neutron, and neutron-proton pairing in nuclear matter. The results,
however, are found to be close to those obtained with charge-independent
potentials.Comment: 5 pages, 3 figures, RevTe
On the Surface Structure of Strange Superheavy Nuclei
Bound, strange, neutral superheavy nuclei, stable against strong decay, may
exist. A model effective field theory calculation of the surface energy and
density of such systems is carried out assuming vector meson couplings to
conserved currents and scalar couplings fit to data where it exists. The
non-linear relativistic mean field equations are solved assuming local baryon
sources. The approach is calibrated through a successful calculation of the
known nuclear surface tension.Comment: 12 pages, 9 figure
Nucleon-Nucleon Optical Model for Energies to 3 GeV
Several nucleon-nucleon potentials, Paris, Nijmegen, Argonne, and those
derived by quantum inversion, which describe the NN interaction for T-lab below
300$ MeV are extended in their range of application as NN optical models.
Extensions are made in r-space using complex separable potentials definable
with a wide range of form factor options including those of boundary condition
models. We use the latest phase shift analyses SP00 (FA00, WI00) of Arndt et
al. from 300 MeV to 3 GeV to determine these extensions. The imaginary parts of
the optical model interactions account for loss of flux into direct or resonant
production processes. The optical potential approach is of particular value as
it permits one to visualize fusion, and subsequent fission, of nucleons when
T-lab above 2 GeV. We do so by calculating the scattering wave functions to
specify the energy and radial dependences of flux losses and of probability
distributions. Furthermore, half-off the energy shell t-matrices are presented
as they are readily deduced with this approach. Such t-matrices are required
for studies of few- and many-body nuclear reactions.Comment: Latex, 40 postscript pages including 17 figure
- …