Helicity skewed quark distributions of the nucleon and chiral symmetry

We compute the helicity skewed quark distributions $\widetilde{H}$ and $\widetilde{E}$ in the chiral quark-soliton model of the nucleon. This model emphasizes correctly the role of spontaneously broken chiral symmetry in structure of nucleon. It is based on the large-N_c picture of the nucleon as a soliton of the effective chiral lagrangian and allows to calculate the leading twist quark- and antiquark distributions at a low normalization point. We discuss the role of chiral symmetry in the helicity skewed quark distributions $\widetilde{H}$ and $\widetilde{E}$. We show that generalization of soft pion theorems, based on chiral Ward identities, leads in the region of -\xi < x < \xi to the pion pole contribution to $\widetilde{E}$ which dominates at small momentum transfer.Comment: 22 pages, 5 figure

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

Nucleon Parton Distributions at Low Normalization Point in the Large N_c Limit

At large N_c the nucleon can be viewed as a soliton of the effective chiral lagrangian. This picture of nucleons allows a consistent nonperturbative calculation of the leading-twist parton distributions at a low normalization point. We derive general formulae for the polarized and unpolarized distributions (singlet and non-singlet) in the chiral quark-soliton model. The consistency of our approach is demonstrated by checking the baryon number, isospin and total momentum sum rules, as well as the Bjorken sum rule. We present numerical estimates of the quark and antiquark distributions and find reasonable agreement with parametrizations of the data at a low normalization point. In particular, we obtain a sizeable fraction of antiquarks, in agreement with the phenomenological analysis.Comment: 38 pages + 5 figures in PostScript, Plain LaTe

Polynomiality of unpolarized off-forward distribution functions and the D-term in the chiral quark-soliton model

Mellin moments of off-forward distribution functions are even polynomials of the skewedness parameter. This constraint, called polynomiality property, follows from Lorentz- and time-reversal invariance. We prove that the unpolarized off-forward distribution functions in the chiral quark-soliton model satisfy the polynomiality property. The proof is an important contribution to the demonstration that the description of off-forward distribution functions in the model is consistent. As a byproduct of the proof we derive explicit model expressions for moments of the D-term and compute the first coefficient in the Gegenbauer expansion for this term.Comment: 18 pages, no figures. Corrections and improvements in section 6. To appear in Phys.Rev.

Hard exclusive electroproduction of decuplet baryons in the large N_c limit

The cross sections and transverse spin asymmetries in the hard exclusive electroproduction of decuplet baryons are calculated in the large N_c limit and found to be comparable to that of octet baryons. Large N_c selection rules for the production amplitudes are derived, leading to new sensitive tests of the spin aspects of the QCD chiral dynamics both in the nonstrange and strange sectors. Importance of such studies for the reliable extraction of the pion form factor from pion electroproduction is explained.Comment: 4 pages, 3 figure

Transversity distributions in the nucleon in the large-N_c limit

We compute the quark and antiquark transversity distributions in the nucleon at a low normalization point of 600 MeV in the large-$N_c$ limit, where the nucleon can be described as a soliton of an effective chiral theory (chiral quark-soliton model). The flavor-nonsinglet distributions, $\delta u(x) - \delta d(x)$ and $\delta\bar u(x) - \delta\bar d(x)$, appear in leading order of the $1/N_c$-expansion, while the flavor-singlet distributions, $\delta u(x) + \delta d(x)$ and $\delta\bar u(x) + \delta\bar d(x)$, are non-zero only in next-to-leading order. The transversity quark and antiquark distributions are found to be significantly different from the longitudinally polarized distributions $\Delta u (x) \pm \Delta d (x)$ and $\Delta\bar u (x) \pm \Delta\bar d (x)$, respectively, in contrast to the prediction of the naive non-relativistic quark model. We show that this affects the predictions for the spin asymmetries in Drell-Yan pair production in transversely polarized pp and ppbar collisions.Comment: 45 pages, 16 figure

Skewed and double distributions in pion and nucleon

We study the non-forward matrix elements of twist-2 QCD light-ray operators and their representations in terms of skewed and double distributions, considering the pion as well as the nucleon. We point out the importance of explicitly including all twist-2 structures in the double distribution representation, which naturally leads to a ``two-component'' structure of the skewed distribution, with different contributions in the regions |X| > xi/2 and |X| < \xi/2. We compute the skewed and double quark distributions in the pion at a low normalization point in the effective chiral theory based on the instanton vacuum. Also, we derive the crossing relations expressing the skewed quark distribution in the pion through the distribution amplitude for two--pion production. Measurement of the latter in two-pion production in gamma^* gamma and gamma^* N reactions could provide direct information about the skewed as well as the usual quark/antiquark-distribution in the pion.Comment: 37 pages, LaTeX. 5 figures included using eps

Hard exclusive pseudoscalar meson electroproduction and spin structure of a nucleon

The amplitude for hard exclusive pseudoscalar meson electroproduction off nucleon (nuclear) targets is computed in QCD within the leading $\alpha_s \ln {Q^2/\lambda_{QCD}^{2}}$ approximation. We show that the distribution of recoil nucleons depends strongly on the angle between the momentum of the recoil nucleon and the polarization vector of the target (or outgoing nucleon). This dependence is especially sensitive to the spin flip skewed parton distribution (SPD) $\widetilde E$. We argue also that the scaling for this spin asymmetry sets in at lower Q^2 than that for the absolute cross section. Basing on the chiral quark-soliton model of the nucleon we estimate quantitatively the spin asymmetry. In the case of pi+ production this asymmetry is dominated at small t by the contribution of the pion pole in the isovector SPD $\widetilde E$ as required by PCAC. In the case of K0 production off a proton we find a large enhancement of the cross section as compared to the case of pi0 production. For the forward production of neutral pseudoscalar mesons off a deuteron target we find the cross section should be zero for the zero deuteron helicity (along the $\gamma^*D$ direction). We consider also cross sections of quasielastic processes off nuclei including the feasibility to implant K+,rho-mesons into nuclear volume.Comment: 19 pages, one figur

Pion and photon light-cone wave functions from the instanton vacuum

The leading-twist wave functions of the pion and the photon at a low normalization point are calculated in the effective low--energy theory derived from the instanton vacuum. The pion wave function is found to be close to the asymptotic one, consistent with the recent CLEO measurements. The photon wave function is non-zero at the endpoints. This different behavior is a consequence of the momentum dependence of the dynamical quark mass suggested by the instanton vacuum. We comment on the relation of meson wave functions and off-forward parton distributions in this model.Comment: 16 pages, LaTeX, 2 figures included using eps

On the Decay of Soliton Excitations

In field theory the scattering about spatially extended objects, such as solitons, is commonly described by small amplitude fluctuations. Since soliton configurations often break internal symmetries, excitations exist that arise from quantizing the modes that are introduced to restore these symmetries. These modes represent collective distortions and cannot be treated as small amplitude fluctuations. Here we present a method to embrace their contribution to the scattering matrix. In essence this allows us to compute the decay widths of such collective excitations. As an example we consider the Skyrme model for baryons and explain that the method helps to solve the long--standing Yukawa problem in chiral soliton models.Comment: 8 pages, to appear in the proceedings (J Phys A) of QFEXT 2007 (Leipzig