550 research outputs found
More rapid climate change promotes evolutionary rescue through selection for increased dispersal distance
Acknowledgements This research was funded by FWO projects G.0057.09 to DB and JB, and G.0610.11 to DB, JB and RS. JMJT, DB and RS are supported by the FWO Research Network EVENET.Peer reviewedPublisher PD
Correlations derived from Modern Nucleon-Nucleon Potentials
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
ESC NN-Potentials in Momentum Space. II. Meson-Pair Exchange Potentials
The partial wave projection of the Nijmegen soft-core potential model for
Meson-Pair-Exchange (MPE) for NN-scattering in momentum space is presented.
Here, nucleon-nucleon momentum space MPE-potentials are NN-interactions where
either one or both nucleons contains a meson-pair vertex. Dynamically, the
meson-pair vertices can be viewed as describing in an effective way (part of)
the effects of heavy-meson exchange and meson-nucleon resonances. From the
point of view of ``duality,'' these two kinds of contribution are roughly
equivalent. Part of the MPE-vertices can be found in the chiral-invariant
phenomenological Lagrangians that have a basis in spontaneous broken chiral
symmetry. It is shown that the MPE-interactions are a very important component
of the nuclear force, which indeed enables a very succesful description of the
low and medium energy NN-data. Here we present a precise fit to the NN-data
with the extended-soft-core (ESC) model containing OBE-, PS-PS-, and
MPE-potentials. An excellent description of the NN-data for
MeV is presented and discussed. Phase shifts are given and a is reached.Comment: 27 pages, 5 PostScript figures, revtex
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.
Soft two-meson-exchange nucleon-nucleon potentials. II. One-pair and two-pair diagrams
Two-meson-exchange nucleon-nucleon potentials are derived where either one or
both nucleons contains a pair vertex. Physically, the meson-pair vertices are
meant to describe in an effective way (part of) the effects of heavy-meson
exchange and meson-nucleon resonances. {}From the point of view of ``duality,''
these two kinds of contribution are roughly equivalent. The various
possibilities for meson pairs coupling to the nucleon are inspired by the
chiral-invariant phenomenological Lagrangians that have appeared in the
literature. The coupling constants are fixed using the linear model.
We show that the inclusion of these two-meson exchanges gives a significant
improvement over a potential model including only the standard one-boson
exchanges.Comment: 21 pages RevTeX, 7 postscript figures; revised version as to appear
in Phys. Rev.
Comment on piNN Coupling from High Precision np Charge Exchange at 162 MeV
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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