Generalized form factors, generalized parton distributions and the spin contents of the nucleon

With a special intention of clarifying the underlying spin contents of the nucleon, we investigate the generalized form factors of the nucleon, which are defined as the $n$-th $x$-moments of the generalized parton distribution functions, within the framework of the chiral quark soliton model. A particular emphasis is put on the pion mass dependence of final predictions, which we shall compare with the predictions of lattice QCD simulations carried out in the so-called heavy pion region around $m_\pi \simeq (700 \sim 900) {MeV}$. We find that some observables are very sensitive to the variation of the pion mass. It will be argued that the negligible importance of the quark orbital angular momentum indicated by the LHPC and QCDSF lattice collaborations might be true in the unrealistic heavy pion world, but it is not necessarily the case in our real world close to the chiral limit.Comment: Final version accepted for publication in Phys. Rev.

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 $F_2^p (x) - F_2^n (x)$, $F_2^n (x) / F_2^p (x)$, the Hermes and NuSea data for $\bar{d}(x) - \bar{u}(x)$, the EMC and SMC data for $g_1^p(x)$, $g_1^n(x)$ and $g_1^d(x)$. Among others, flavor asymmetry of the longitudinally polarized sea-quark distributions is a remarkable prediction of this model, i.e., it predicts that $\Delta \bar{d}(x) - \Delta \bar{u}(x) = C x^{\alpha} [ \bar{d}(x) - \bar{u}(x)]$ with a sizable negative coefficient $C \simeq -2.0$ (and $\alpha \simeq 0.12$) in qualitative consistency with the recent semi-phenomenological analysis by Morii and Yamanishi.Comment: 14pages, including 5 eps_figures with epsbox.sty, late

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 $\Delta m_s$ 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 $\bar{d} (x) - \bar{u} (x), \bar{d} (x) / \bar{u} (x), \Delta \bar{u} (x) - \Delta \bar{d} (x)$ as well as on the {\it particle-antiparticle asymmetry} of the strange quark distributions represented by $s (x) - \bar{s} (x), s (x) / \bar{s} (x), \Delta s (x) - \Delta \bar{s} (x)$ 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 $\bar{d} (x) - \bar{u} (x)$, the E866 data for $\bar{d} (x) / \bar{u} (x)$, the CCFR data and Barone et al.'s fit for $s (x) / \bar{s} (x)$ etc. The model is shown to give several unique predictions also for the spin-dependent sea-quark distribution, such that $\Delta s (x) \ll \Delta \bar{s}(x) \lesssim 0$ and $\Delta \bar{d}(x) < 0 < \Delta \bar{u}(x)$, 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

Chiral-odd generalized parton distributions, transversity decomposition of angular momentum, and tensor charges of the nucleon

The forward limit of the chiral-odd generalized parton distributions (GPDs) and their lower moments are investigated within the framework of the chiral quark soliton model (CQSM), with particular emphasis upon the transversity decomposition of nucleon angular momentum proposed by Burkardt. A strong correlation between quark spin and orbital angular momentum inside the nucleon is manifest itself in the derived second moment sum rule within the CQSM, thereby providing with an additional support to the qualitative connection between chiral-odd GPDs and the Boer-Mulders effects. We further confirm isoscalar dominance of the corresponding first moment sum rule, which indicates that the Boer-Mulders functions for the $u$- and $d$-quarks have roughly equal magnitude with the same sign. Also made are some comments on the recent empirical extraction of the tensor charges of the nucleon by Anselmino et al. We demonstrate that a comparison of their result with any theoretical predictions must be done with great care, in consideration of fairly strong scale dependence of tensor charges, especially at lower renormalization scale.Comment: version to appear in Phys. Rev.

Melanin-based plumage coloration and melanin content in organs in the barn owl.

Although the evolutionary ecology of melanin pigments and melanin-based coloration has been studied in great details, particularly in birds, little is known about the function of melanin stored inside the body. In the barn owl Tyto alba, in which individuals vary in the degree of reddish pheomelanin-based coloration and in the size of black eumelanic feather spots, we measured the concentration in melanin pigments in seven organs. The eyes had by far the most melanin then the skin, pectoral muscle, heart, liver, trachea, and uropygial gland. The concentration in eumelanin was not necessarily correlated with the concentration in pheomelanin suggesting that their production can be regulated independently from each other. Redder barn owls had more pheomelanin in the skin and uropygial gland than white owls, while owls displaying larger black feather spots had more eumelanin in the skin than small-spotted owls. More data are required to evaluate whether melanin-based traits can evolve as an indirect response to selection exerted on melanin deposition in organs

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 $m_{\rm s}$. 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 $1/N_{\rm c}$ 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