14,844 research outputs found
Electromagnetic corrections to p scattering length from pionic hydrogen
We derive a closed, model space independent, expression for the
electromagnetic correction factor to the scattering length
extracted from a hydrogenic atom with an extended charge to order
and in the limit of a short ranged hadronic interaction.Comment: 4 pages; PANIC02, XVIth Conference on Particles and Nuclei, Osaka, to
appear in Nuclear Physics
Chiral Lagrangians and Quark Condensate in Nuclei
We study the evolution with density of the quark condensate in the nuclear
medium with interacting nucleons and including the short range correlations. We
work with two chiral models, the linear sigma model and the non-linear one. For
the last one we use two versions, one which does not satisfy PCAC, and another
one which does. We show that the quark condensate, as other observables, is
independent on the variant selected. The application to physical pions excludes
the linear sigma model as a credible one. In the non-linear models our
conclusions are: first there is no systematic reaction imposed by chiral
symmetry against symmetry restoration, second, if one keeps only the s-wave
pion-nucleon interaction, the quark condensate evolves essentially linearly
with density, as if the nucleons were non interacting. The main correction
arises from the p-wave pion-nucleon interaction. Last, in the s-wave optical
potential, chiral symmetry tolerates but does not impose two body terms. On the
other hand the effect of correlations linked to the isospin symmetric amplitude
is negligible.Comment: 24 pages, LaTex, 7 PostScript Figures, a couple of misprints
corrected , 2 references added, a few modifications of the main text and
conclusion, to be published in Nucl. Phys.
Scalar response of the nucleon chiral symmetry and nuclear matter properties
In this talk we present a description of nuclear binding in a chiral approach
based on the existence of a chiral invariant scalar field associated with the
generation of the masses through spontaneous chiral symmetry breaking. We
discuss the emergence of such a field on the example of the NJL model. We also
incorporate the effect of confinement at the level of the nucleon substructure
to stabilize nuclear matter. In a particular quark-diquark model we illustrate
the simutaneous influences of spontaneous chiral symmetry breaking and
confinement on the nucleon mass and on the nuclear matter description.Comment: Talk given by G. chanfray at "Achievements and New Directions in
Subatomic Physics: Workshop in Honour of Tony Thomas' 60th Birthday Adelaide,
South Australia. February 15 - February 19, 2010"
QCD susceptibilities and nuclear matter saturation in a chiral theory: inclusion of pion loops
We derive the equation of state of symmetric nuclear matter in a relativistic
theory with and exchange. We take a chiral version of this
model which insures all the chiral constraints. Going beyond the mean field
approach we introduce the effects of the pion loops. For the parameters of the
model, in order to fix those linked to pion exchange, we exploit the most
recent information on the short-range part of the spin-isospin interaction. For
those linked to the scalar meson exchange we make use of an analysis of lattice
results on the nucleon mass evolution with the quark mass. With these inputs we
are able reach a correct description of the saturation properties. From the
equation of state of symmetric nuclear matter we alsoderive the density
dependence of the quark condensate and of the QCD susceptibilities
Relativistic Chiral Theory of Nuclear Matter and QCD Constraints
We present a relativistic chiral theory of nuclear matter which includes the
effect of confinement. Nuclear binding is obtained with a chiral invariant
scalar background field associated with the radial fluctuations of the chiral
condensate Nuclear matter stability is ensured once the scalar response of the
nucleon depending on the quark confinement mechanism is properly incorporated.
All the parameters are fixed or constrained by hadron phenomenology and lattice
data. A good description of nuclear saturation is reached, which includes the
effect of in-medium pion loops. Asymmetry properties of nuclear matter are also
well described once the full rho meson exchange and Fock terms are included.Comment: Talk given by G. Chanfray at PANIC 08, Eilat (Israel), november
10-14, 200
Inclusive and pion production neutrino-nucleus cross sections
We analyze the experimental data on the inclusive double differential cross
section by neutrinos charged current, measured by T2K, with the same model
which was successful for the MiniBooNE quasielastic cross sections. As in our
previous analysis the multinucleon component is needed in order to reproduce
the data. For the total cross section our evaluation is smaller than the
SciBooNE data above 1 GeV. This indicates the opening of a new channel not
included in our evaluation, presumably the two pion emission channel. We also
check that our description holds for the exclusive single pion production
channel by confronting our evaluation with the MiniBooNE double differential
cross section for a single charged pion and the Q^2 distribution. Both are
compatible with data
Relation between growth characteristics and yield of barley in different environments
The increasing interest in organic farming has increased the interest in examining the importance of the different growing characteristics, such as attack of diseases, grain weight, lodging and heading date. One of the important questions raised was whether the relationship between the growing characteristics and yield would be the same for conventionally and organically grown crop or would some growing characteristics be more important for organically than for conventionally grown crops. This work will focus on that question.
The analyses are performed using two datasets with comparable trials in both conventional and organic grown systems for barley (Hordeum vulgare). The two datasets were from Sweden and Denmark. From Sweden 22 conventional and 22 organic grown trials were available. The trials were laid out at 4 locations in Northern Sweden during the years from 1994-2003. The number of varieties per trial varied between 7 and 15 and 50 varieties were represented. Most of the trials were laid out as split-plot designs with 2 nitrogen levels in the conventional grown trial and 2 seed rates in the organic grown trials. From Denmark 4 conventional and 4 organic grown trials were available. The trials were laid out as a-designs at 2 locations in 2 years (2003 and 2004).
The number of varieties per trial varied between 108 and 113 and 146 varieties were represented. The data from each country were analysed in a linear mixed model. The effects of location, year, variety, their interaction and interaction with system were included as random effect. The effect of growing system and growing characteristics were included as fixed effects to see how much of the variation caused by varieties and interaction with varieties that could be explained by the growing characteristic and to se if the effect of the growing characteristics depended on the growing system.
The analyses showed that the growing characteristics could explain a considerable part of the variance components for variety or interaction with variety. The effect of some growing characteristics depended significantly on the growing system, but the results varied to some extent between the two countries. In Sweden the effect of volume weight were more important in the conventional grown trials than in the organic grown trials whereas in Denmark grain weight was more important in the organic grown trials than in the conventional grown trials. In Denmark powdery mildew decreased the yield significantly more in conventional grown trials than in organic grown trials. In most cases the other diseases decreased the yield more in the organic grown trials than in the conventional grown trials. In some models the yield in organic grown trials increased as the level of scald attach increased. The results indicated that the effect of a given disease level decreased the yield more in the conventional grown trials than in the organic grown trials â or in some cases increased the yield in the organic grown trial while the yield in conventionally grown trials were increased less or decreased
Neutrino versus antineutrino cross sections and CP violation
We discuss the nuclear interactions of neutrinos versus those of
antineutrinos, a relevant comparison for CP violation experiments in the
neutrino sector. We consider the MiniBooNE quasielastic-like double
differential neutrinos and antineutrinos cross sections which are flux
dependent and hence specific to the MiniBooNE set-up. We combine them
introducing their sum and their difference. We show that the last combination
can bring a general information, which can be exploited in other experiments,
on the nuclear matrix elements of the axial vector interference term. Our
theoretical model reproduces well the two cross sections combinations. This
confirms the need for a sizeable multinucleon component in particular in the
interference term
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