On Gauge-Invariant Decomposition of Nucleon Spin

We investigate the relation between the known decompositions of the nucleon spin into its constituents, thereby clarifying in what respect they are common and in what respect they are different essentially. The decomposition recently proposed by Chen et al. can be thought of as a nontrivial generalization of the gauge-variant Jaffe-Manohar decomposition so as to meet the gauge-invariance requirement of each term of the decomposition. We however point out that there is another gauge-invariant decomposition of the nucleon spin, which is closer to the Ji decomposition, while allowing the decomposition of the gluon total angular momentum into the spin and orbital parts. After clarifying the reason why the gauge-invariant decomposition of the nucleon spin is not unique, we discuss which decomposition is more preferable from the experimental viewpoint.Comment: The version to appear in Phys. Rev.

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

The role of orbital angular momentum in the proton spin

The orbital angular momenta $L^u$ and $L^d$ 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 $L^u - L^d$ 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.

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

On the physics behind the form factor ratio μpGEp(Q2)/GMp(Q2)\mu_p G_E^p (Q^2) / G_M^p (Q^2)

We point out that there exist two natural definitions of the nucleon magnetization densities : the density $\rho_M^K (r)$ introduced in Kelly's phenomenological analysis and theoretically more standard one $\rho_M (r)$. We can derive an explicit analytical relation between them, although Kelly's density is more useful to disentangle the physical origin of the different $Q^2$ dependence of the Sachs electric and magnetic form factors of the nucleon. We evaluate both of $\rho_M (r)$ and $\rho_M^K (r)$ as well as the charge density $\rho_{ch}(r)$ of the proton within the framework of the chiral quark soliton model, to find a noticeable qualitative difference between $\rho_{ch}(r)$ and $\rho_M^K (r)$, which is just consistent with Kelly's result obtained from the empirical information on the Sachs electric and magnetic form factors of the proton.Comment: 12 pages, 5 figures. version to appear in J. Phys. G.: Nucl. Part. Phy

Distance Measurement of Galaxies to Redshift of 0.1 using the CO-Line Tully-Fisher Relation

We report on the first results of a long-term project to derive distances of galaxies at cosmological distances by applying the CO-line width-luminosity relation. We have obtained deep CO-line observations of galaxies at redshifts up to 29,000 km/s using the Nobeyama 45-m mm-wave Telescope, and some supplementary data were obtained by using the IRAM 30-m telescope. We have detected the CO line emission for several galaxies, and used their CO line widths to estimate the absolute luminosities using the line-width-luminosity relation. In order to obtain photometric data and inclination correction, we also performed optical imaging observations of the CO-detected galaxies using the CFHT 3.6-m telescope at high resolution. The radio and optical data have been combined to derive the distance moduli and distances of the galaxies, and Hubble ratios were estimated for these galaxies. We propose that the CO line width-luminosity relation can be a powerful method to derive distances of galaxies to redfhift of z = 0.1 and to derive the Hubble ratio in a significant volume of the universe. Key words: Cosmology - Galaxies: general - Distance scale - CO lineComment: To appear in PASJ, Plain Tex, 3 figures (in 10 ps files

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.

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 $x$.Comment: 19 pages, 8 Figures, LaTeX, some typos corrected, some additional comments in the conclusion

Azimuthal dependence of the density distribution in outer galactic discs accreting intergalactic flows

AIMS. The amplitude and scaleheight of the Galactic gas disc density are not axisymmetric against expectations in a self-gravity axisymmetric disc. However, this lopsidedness can be explained in terms of intergalactic accretion flows, which produce non-axisymmetric pressure on the disc. This mechanism could be also responsible for the formation of a warp. METHODS. We analytically derive the relationship between the disc density and the self-gravity and external pressure. RESULTS. The same scenario of accretion as we proposed years ago to explain the formation of the warp explains the azimuthal dependence of the density and its scaleheight, with minimum/maximum in the positions of maximum amplitude of the warp (phi=95 deg. and 275 deg.), as expected from its pressure distribution.Comment: 4 pages, accepted to be published in A&A-letter

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