864 research outputs found
Do we expect light flavor sea-quark asymmetry also for the spin-dependent distribution functions of the nucleon?
After taking account of the scale dependence by means of the standard DGLAP
evolution equation, the theoretical predictions of the chiral quark soliton
model for the unpolarized and longitudinally polarized structure functions of
the nucleon are compared with the recent high energy data. The theory is shown
to explain all the qualitative features of the experiments, including the NMC
data for , , the Hermes and NuSea
data for , the EMC and SMC data for ,
and . Among others, flavor asymmetry of the longitudinally
polarized sea-quark distributions is a remarkable prediction of this model,
i.e., it predicts that with a sizable negative coefficient
(and ) in qualitative consistency with the recent
semi-phenomenological analysis by Morii and Yamanishi.Comment: 14pages, including 5 eps_figures with epsbox.sty, late
The role of orbital angular momentum in the proton spin
The orbital angular momenta and of up and down quarks in the
proton are estimated as functions of the energy scale as model-independently as
possible, on the basis of Ji's angular momentum sum rule. This analysis
indicates that is large and negative even at low energy scale of
nonperturbative QCD, in contrast to Thomas' similar analysis based on the
refined cloudy bag model. We pursuit the origin of this apparent discrepancy
and suggest that it may have a connection with the fundamental question of how
to define quark orbital angular momenta in QCD.Comment: 14 pages, 3 figures, 1 table A slightly extended version to appear in
Eur. Phys. J.
Light-flavor sea-quark distributions in the nucleon in the SU(3) chiral quark soliton model (I) -- phenomenological predictions --
Theoretical predictions are given for the light-flavor sea-quark
distributions including the strange quark ones on the basis of the flavor SU(3)
version of the chiral quark soliton model. Careful account is taken here of the
SU(3) symmetry breaking effects due to the mass difference between the strange
and nonstrange quarks. This effective mass difference between the
strange and nonstrange quarks is the only one parameter necessary for the
flavor SU(3) generalization of the model. A particular emphasis of study is put
on the {\it light-flavor sea-quark asymmetry} as exemplified by the observables
as well as on the {\it particle-antiparticle asymmetry} of
the strange quark distributions represented by etc. As for the unpolarized
sea-quark distributions, the predictions of the model seem qualitatively
consistent with the available phenomenological information provided by the NMC
data for , the E866 data for , the CCFR data and Barone et al.'s fit for etc. The
model is shown to give several unique predictions also for the spin-dependent
sea-quark distribution, such that and , although the verification
of these predictions must await more elaborate experimental investigations in
the near future.Comment: 36 pages, 20 EPS figures. The revised version accepted for
publication in Phys. Rev. D. The title has been changed, and the body of the
paper has been divided into two pieces, i.e.. the present one which discusses
the main phenomenological predictions of the model and the other one which
describes the detailed formulation of the flavor SU(3) chiral quark soliton
model to predict light-flavor quark and antiquark distribution functions in
the nucleo
Chiral Symmetry and the Nucleon Structure Functions
The isospin asymmetry of the sea quark distribution as well as the
unexpectedly small quark spin fraction of the nucleon are two outstanding
discoveries recently made in the physics of deep-inelastic structure functions.
We evaluate here the corresponding quark distribution functions within the
framework of the chiral quark soliton model, which is an effective quark model
of baryons maximally incorporating the most important feature of low energy
QCD, i.e. the chiral symmetry and its spontaneous breakdown. It is shown that
the model can explain qualitative features of the above-mentioned nucleon
structure functions within a single framework, thereby disclosing the
importance of chiral symmetry in the physics of high energy deep-inelastic
scatterings.Comment: 20pages, LaTex, 5 Postscript figures A numerical error of the
original version was corrected. The discussion on the regularization
dependence of distribution functions has been added. A comparison with the
low energy-scale parametrization of Gloeck, Reya and Vogt has been mad
Parton distributions in the chiral quark model: a continuum computation
We compute the parton distributions for the chiral quark model. We present a
new technique for performing such computations based on Green functions. This
approach avoids a discretization of the spectrum. It therefore does not need
any smoothing procedures.
The results are similar to those of other groups, however the distributions
peak at smaller .Comment: 19 pages, 8 Figures, LaTeX, some typos corrected, some additional
comments in the conclusion
New positivity bounds on polarized parton distributions in multicolored QCD
We derive new positivity bounds on spin-dependent parton distributions in
multicolored QCD. They are stronger than Soffer inequality. We check that the
new inequalities are stable under one-loop DGLAP evolution to higher
normalization points.Comment: 4 pages, typos corrected, more details, references adde
Magnetic moments of the SU(3) decuplet baryons in the chiral quark-soliton model
Magnetic moments of baryons are studied within the chiral quark soliton model
with special emphasis on the decuplet of baryons. The model is used to identify
all symmetry breaking terms proportional to . Sum rules for the
magnetic moments are derived. A ``model-independent'' analysis of the symmetry
breaking terms is performed and finally model calculations are presented, which
show the importance of the rotational corrections for cranking of
the soliton.Comment: 22 pages, RevTex. The final version accepted for publication in Phys.
Rev.
Isovector unpolarized quark distribution in the nucleon in the large-N_c limit
We calculate the isovector (flavor-nonsinglet) unpolarized quark- and
antiquark distributions in the nucleon at a low normalization point in the
large-N_c limit. The nucleon is described as a soliton of the effective chiral
theory. The isovector distribution appears in the next-to-leading order of the
1/N_c-expansion. Numerical results for the quark- and antiquark distributions
compare well with the parametrizations of the data at a low normalization
point. This large-N_c approach gives a flavor asymmetry of the antiquark
distribution (violation of the Gottfried sum rule) in good agreement with the
measurements.Comment: 31 pages, LaTeX, 1 table, 4 figures included using eps
Exploring the proton spin structure
Understanding the spin structure of the proton is one of the main challenges
in hadronic physics. While the concepts of spin and orbital angular momentum
are pretty clear in the context of non-relativistic quantum mechanics, the
generalization of these concepts to quantum field theory encounters serious
difficulties. It is however possible to define meaningful decompositions of the
proton spin that are (in principle) measurable. We propose a summary of the
present situation including recent developments and prospects of future
developments.Comment: 8 pages, 1 figure, 2 tables, contribution to the proceedings of the
DAE-BRNS High Energy Physics Symposium 2014, Dec 8-12, Guwahati, Indi
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