507 research outputs found
Nuclear Shadowing in the Structure Function
Nuclear modification of the structure function is investigated.
Although it could be estimated in the medium and large regions from the
nuclear structure function , it is essentially unknown at small . The
nuclear structure function at small is investigated in two
different theoretical models: a parton-recombination model with rescaling
and an aligned-jet model. We find that these models predict completely
different behavior at small : {\it antishadowing} in the first parton model
and {\it shadowing} in the aligned-jet model. Therefore, studies of the ratio
at small could be useful in discriminating among different
models, which produce similar shadowing behavior in the structure function
. We also estimate currently acceptable nuclear modification of at
small by using experimental data and baryon-number
conservation.Comment: 10 pages, Latex, Figs.1 and 2 are not included, Complete postscript
file including the figures is available at
ftp://ftp.cc.saga-u.ac.jp/pub/paper/riko/quantum1/saga-he-78.ps.gz or at
http://www.cc.saga-u.ac.jp/saga-u/riko/physics/quantum1/structure.htm
Pions in the nuclear medium and Drell-Yan scattering
We investigate the modification of the pion-cloud in the nuclear medium and
its effect on the nuclear Drell-Yan process. The pion's in-medium self-energy
is calculated in a self-consistent delta-hole model, with particle-hole
contribution also included. Both the imaginary and real part of the pion's and
delta's self-energy are taken into account and related through a dispersion
relation assuring causality. The resulting in-medium pion light-cone momentum
distribution shows only a slight enhancement compared to the one of the free
nucleon. As a consequence the ratio of the cross-section for Drell-Yan
scattering on nuclear matter and nucleonic target is close to unity in
agreement with experiment.Comment: 33 pages, Latex with epsf, figures included, to appear in Phys. Rev.
Nuclear Shadowing in a Parton Recombination Model
Deep inelastic structure functions are investigated in a
rescaling model with parton recombination effects. We find that the model can
explain experimentally measured structure functions reasonably well
in the wide Bjorken range (). In the very small region
(), recombination results are very sensitive to input sea-quark and
gluon distributions.Comment: preprint MKPH-T-93-04, IU/NTC 92-20, 25 pages, TEX file (without
Figs. 1-14)., (address after April 1: Saga U., Japan
A Light Front Treatment of the Nucleus-Implications for Deep Inelastic Scattering
A light front treatment of the nuclear wave function is developed and
applied, using the mean field approximation, to infinite nuclear matter. The
nuclear mesons are shown to carry about a third of the nuclear plus momentum,
p+; but their momentum distribution has support only at p+ =0, and the mesons
do not contribute to nuclear deep inelastic scattering. This zero mode effect
occurs because the meson fields are independent of space-time position.Comment: 11 pages, revtex, 1 figur
Pion Excess, Nuclear Correlations, and the Interpretation of () Spin Transfer Experiments
Conventional theories of nuclear interactions predict a net increase in the
distribution of virtual pions in nuclei relative to free nucleons. Analysis of
data from several nuclear experiments has led to claims of evidence against
such a pion excess. These conclusions are usually based on a collective theory
(RPA) of the pions, which may be inadequate. The issue is the energy dependence
of the nuclear response, which differs for theories with strong NN correlations
from the RPA predictions. In the present paper, information about the energy
dependence is extracted from sum rules, which are calculated for such a
correlated, noncollective nuclear theory. The results lead to much reduced
sensitivity of nuclear reactions to the correlations that are responsible for
the pion excess. The primary example is spin transfer, for
which the expected effects are found to be smaller than the experimental
uncertainties. The analysis has consequences for Deep Inelastic Scattering
(DIS) experiments as well.Comment: 16 pages, LaTeX, no figures, submitted to Phys. Rev.
Structure Functions of the Nucleon in a Statistical Model
Deep inelastic scattering is considered in a statistical model of the
nucleon. This incorporates certain features which are absent in the standard
parton model such as quantum statistical correlations which play a role in the
propagation of particles when considering Feynman diagrams containing internal
lines. The inclusion of the corrections in our numerical
calculations allows a good fit to the data for . The fit
corresponds to values of temperature and chemical potential of approximately
GeV and GeV. The latter values of parameters, however,
give rise, for all , to a large value for .Comment: 16 pages TeX, 11 figures available as Postscript files, University of
Bielefeld preprint BI-TP 93/3
Developing a framework for the analysis of power through depotentia
Stakeholder participation in tourism policy-making is usually perceived as providing a means of empowerment. However participatory processes drawing upon stakeholders from traditionally empowered backgrounds may provide the means of removing empowerment from stakeholders. Such an outcome would be in contradiction to the claims that participatory processes improve both inclusivity and sustainability. In order to form an understanding of the sources through which empowerment may be removed, an analytical perspective has been developed deriving from LukesĂŻÂżÂœs views of power dating from 1974. This perspective considers the concept of depotentia as the removal of ĂŻÂżÂœpower toĂŻÂżÂœ without speculating upon the underlying intent and also provides for the multidimensionality of power to be examined within a single study. The application of this analytical perspective has been tested upon findings of the government-commissioned report of the Countryside and Community Research Unit in 2005. The survey and report investigated the progress of Local Access Forums in England created in response to the Countryside and Rights of Way Act 2000. Consideration of the data from this perspective permits the classification of individual sources of depotentia which can each be addressed and potentially enable stakeholder groups to reverse loss of empowerment where it has occurred
Instantons And Baryon Mass Splittings in the MIT Bag Model
The contribution of instanton-induced effective inter-quark interactions to
the baryon mass splittings was considered in the bag model. It is found that
results are different from those obtained in the constituent quark model where
the instanton effects are like those from one-gluon exchange. This is because
in the context of the bag model calculation the one-body instanton-induced
interaction has to be included.Comment: 23 pages, report ZTF-93/10 (to appear in Phys.Rev. D
Return of the EMC Effect: Finite Nuclei
A light front formalism for deep inelastic lepton scattering from finite
nuclei is developed. In particular, the nucleon plus momentum distribution and
a finite system analog of the Hugenholtz-van Hove theorem are presented. Using
a relativistic mean field model, numerical results for the plus momentum
distribution and ratio of bound to free nucleon structure functions for Oxygen,
Calcium and Lead are given. We show that we can incorporate light front physics
with excellent accuracy while using easily computed equal time wavefunctions.
Assuming nucleon structure is not modified in-medium we find that the
calculations are not consistent with the binding effect apparent in the data
not only in the magnitude of the effect, but in the dependence on the number of
nucleons.Comment: 11 pages, 6 figure
A Proposed Test of Charge Symmetry in Decay
The semi-leptonic decays of offer a vehicle for observing charge
symmetry-breaking. The effect is expected to be about 6\%, enhanced due to the
replacement of two u quarks by d quarks. We propose that present experimental
data be improved to search for this effect.Comment: 6 pages, submitted to Physical Review D, Brief Reports, Report #
DOE/ER/40427-14-N9
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