446 research outputs found
TWO-PION EXCHANGE NUCLEAR POTENTIAL - CHIRAL CANCELLATIONS
We show that chiral symmetry is responsible for large cancellations in the
two-pion exchange nucleon-nucleon interaction, which are similar to those
occuring in free pion-nucleon scattering.Comment: REVTEX style, 5 pages, 3 PostScrip figures compressed, tarred and
uuencode
NN Scattering: Chiral Predictions for Asymptotic Observables
We assume that the nuclear potential for distances larger than 2.5 fm is
given just by the exchanges of one and two pions and, for the latter, we adopt
a model based on chiral symmetry and subthreshold pion-nucleon amplitudes,
which contains no free parameters. The predictions produced by this model for
nucleon-nucleon observables are calculated and shown to agree well with both
experiment and those due to phenomenological potentials.Comment: 16 pages, 12 PS figures included, to appear in Physical Review
Solutions of the bound state Faddeev-Yakubovsky equations in three dimensions by using NN and 3N potential models
A recently developed three-dimensional approach (without partial-wave
decomposition) is considered to investigate solutions of Faddeev-Yakubovsky
integral equations in momentum space for three- and four-body bound states,
with the inclusion of three-body forces. In the calculations of the binding
energies, spin-dependent nucleon-nucleon (NN) potential models (named, S,
MT-I/III, YS-type and PGL) are considered along with the scalar
two-meson exchange three-body potential. Good agreement of the presently
reported results with the ones obtained by other techniques are obtained,
demonstrating the advantage of an approach in which the formalism is much more
simplified and easy to manage for direct computation.Comment: 16 pages, 1 figure and 6 tables; to appear in Physical review
Quark Condensate in the Deuteron
We study the changes produced by the deuteron on the QCD quark condensate by
means the Feynman-Hellmann theorem and find that the pion mass dependence of
the pion-nucleon coupling could play an important role. We also discuss the
relation between the many body effect of the condensate and the meson exchange
currents, as seen by photons and pions. For pion probes, the many-body term in
the physical amplitude differs significantly from that of soft pions, the one
linked to the condensate. Thus no information about the many-body term of the
condensate can be extracted from the pion-deuteron scattering length. On the
other hand, in the Compton amplitude, the relationship with the condensate is a
more direct one.Comment: to appear in Physics Review C (19 pages, 3 figures
PERSYST, a model for ex ante assessment of cropping systems performances. Adaptation to organic farming in the Ile-de-France region
PERSYST is a web software for ex ante assessment of crop yield that takes explicitely into account the cropping system (i.e. crop rotation and crop management) perspective. Environmental and economic indicators are calculated at crop rotation scale to complete the previous yield assessment. In 2012, a research program enabled the model adaptation to organic systems, taking into account weed management and organic inputs supply. This program also allowed to parameterize the web software in the Ile-de-France region for 8 soil types and 18crops. Parameterization has been validated for the most common situations. Validation remains to be done for less common ones. When completed, validation will make it possible to test the software in promising situations of use, such as supporting organic farmers analyzing their current cropping systems, or supporting farmers thinking about converting their farms to organic farming
The Contribution of the Light Quark Condensate to the Pion-Nucleon Sigma Term
There has been a discrepancy between values of the pion-nucleon sigma term
extracted by two different methods for many years. Analysis of recent high
precision pion-nucleon data has widened the gap between the two determinations.
It is argued that the two extractions correspond to different quantities and
that the difference between them can be understood and calculated.Comment: Modern Physics Letters A (in press
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