arXiv subjects

M. V. Polyakov

Publications and source records attributed to M. V. Polyakov.

At least 55 records · Page 3Linked to original sources

arXiv2005

SU(3) systematization of baryons

We review the spectrum of all baryons with the mass less than approximately 2000-2200 MeV using methods based on the approximate flavor SU(3) symmetry of the strong interaction. The application of the Gell-Mann--Okubo mass formulas and SU(3)-symmetric predictions for two-body hadronic decays allows us to successfully catalogue almost all known baryons in twenty-one SU(3) multiplets. In order to have complete multiplets, we predict the existence of several strange particles, most notably the Λhyperon with J^P=3/2^-, the mass around 1850 MeV, the total width approximately 130 MeV, significant branching into the Σπand Σ(1385) πstates and a very small coupling to the N \bar{K} state. Assuming that the antidecuplet exists, we show how a simple scenario, in which the antidecuplet mixes with an octet, allows to understand the pattern of the antidecuplet decays and make predictions for the unmeasured decays.

hep-ph↗

arXiv2005

Extraction of radiative decay width for the non-strange partner of Theta^+

Using the results of the GRAAL collaboration on the ηphotoproduction from the neutron target, we attempt to extract the partial radiative width of the possible new nucleon resonance N^*(1675). The obtained estimates support this resonance to be a very attractive candidate for the non-strange member of the exotic antidecuplet of baryons -- a partner of the Θ^+ pentaquark. Our phenomenological value for the transition magnetic moment μ(n^* n), appears to be in good agreement with predictions of the Chiral Quark Soliton Model.

hep-ph↗

arXiv2005

Dual parameterization of generalized parton distributions and description of DVCS data

We discuss a new leading-order parameterization of generalized parton distributions of the proton, which is based on the idea of duality. In its minimal version, the parameterization is defined by the usual quark singlet parton distributions and the form factors of the energy-momentum tensor. We demonstrate that our parameterization describes very well the absolute value, the Q^2-dependence and the W-dependence of the HERA data on the total DVCS cross section and contains no free parameters in that kinematics. The parameterization suits especially well the low-x_{Bj} region, which allows us to advocate it as a better alternative to the frequently used double distribution parameterization of the GPDs.

hep-ph↗

arXiv2005

Photoproduction of the Theta^+ resonance on the nucleon in a Regge model

We estimate the reaction mechanisms for the photoproduction of the Theta^+(1540) resonance on the nucleon, through K and K^* Regge exchanges. We compare the size of the cross sections for the gamma n -> K^- Theta^+ and gamma p -> K^0 bar Theta^+ reactions, and investigate their sensitivity to the spin-parity assignments J^P = 1/2^\pm, 3/2^\pm for the Theta^+ resonance. The model allows to estimate the cross sections corresponding with a given upper bound on the width of the Theta^+. Within this model, the cross sections on the neutron are found to be around a factor 5 larger than the ones on the proton, due to the presence of charged K exchange for the reaction on a neutron target. Furthermore, the photon asymmetry is found to display a pronounced sensitivity to the parity of the Theta^+, making it a very promising observable to help determining the quantum numbers of the Theta^+ resonance.

hep-ph↗

arXiv2005

The generalized parton distribution function (E^u+E^d)(x,xi,t) of the nucleon in the chiral quark soliton model

The unpolarized spin-flip isoscalar generalized parton distribution function (E^u+E^d)(x,xi,t) is studied in the large-Nc limit at a low normalization point in the framework of the chiral quark-soliton model. This is the first study of generalized parton distribution functions in this model, which appear only at the subleading order in the large-Nc limit. Particular emphasis is put therefore on the demonstration of the theoretical consistency of the approach. The forward limit of (E^u+E^d)(x,xi,t) of which only the first moment -- the anomalous isoscalar magnetic moment of the nucleon -- is known phenomenologically, is computed numerically. Observables sensitive to (E^u+E^d)(x,xi,t) are discussed.

hep-ph↗

arXiv2005

Present status of the nonstrange and other flavor partners of the exotic Theta+ baryon

Given the existing empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F-partners, paying special attention to the nonstrange member of the antidecuplet N*. The modified piN partial-wave analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases, the N* should be rather narrow and highly inelastic. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons. Recent experimental evidence from the GRAAL and STAR Collaborations could be interpreted as observations of a candidate for the Theta+ nonstrange partner.

hep-ph↗

arXiv2005

Mixing and decays of the antidecuplet in the context of approximate SU(3) symmetry

We consider mixing of the antidecuplet with three J^P=1/2^+ octets (the ground-state octet, the octet containing N(1440), Λ(1600), Σ(1660) and Ξ(1690) and the octet containing N(1710), Λ(1800), Σ(1880) and Ξ(1950)) in the framework of approximate flavor SU(3) symmetry. We give general expressions for the partial decay widths of all members of the antidecuplet as functions of the two mixing angles. Identifying N_{anti-10} with the N(1670) observed by the GRAAL experiment, we show that the considered mixing scenario can accommodate all present experimental and phenomenological information on the Θ^+ and N_{anti-10} decays: Θ^+ could be as narrow as 1 MeV; the N_{anti-10} -> N + ηdecay is sizable, while the N_{anti-10} ->N + πdecay is suppressed and the N_{anti-10} ->Λ+ K decay is possibly suppressed. Constraining the mixing angles by the N_{anti-10} decays, we make definite predictions for the Σ_{anti-10} decays. We point out that Σ_{anti-10} with mass near 1770 MeV could be searched for in the available data on K_S p invariant mass spectrum, which already revealed the Θ^+ peak. It is important to experimentally verify the decay properties of Σ(1770) because its mass and J^P=1/2^+ make it an attractive candidate for Σ_{anti-10}.

hep-ph↗

arXiv2004

Notes on exotic anti-decuplet of baryons

We emphasize the importance of identifying non-exotic SU(3) partners of the Theta^+ pentaquark, and indicate possible ways how to do it. We also use the soliton picture of baryons to relate Reggeon couplings of various baryons. These relations are used to estimate the Theta^+ production cross section in high energy processes. We show that the corresponding cross sections are significantly suppressed relative to the production cross sections of usual baryons. Finally, we present spin non-flip form factors of the anti-decuplet baryons in the framework of the chiral quark soliton model.

hep-ph↗

arXiv2004

Soft Pion Emission from the Nucleon Induced by Twist-2 Light-Cone Operators

We compute the matrix elements for pion emission from the nucleon induced by twist-two light-cone operators in the kinematics where the pion is close to threshold. It is shown that the results of heavy baryon ChPT are in agreement with the results from the soft-pion theorem approach. Therefore the amplitude of soft-pion emission is directly related to the generalized parton distributions in the nucleon.

nucl-th↗

arXiv2004

Nonstrange and other unitarity partners of the exotic Theta+ baryon

Given presently known empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F partners, paying special attention to the nonstrange member of the antidecuplet N*. The modified PWA analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases the N* should be highly inelastic. The theoretical analysis, based on the soliton picture and assumption of Gamma(Theta+) < 5 MeV, shows that most probably Gamma(N*) < 30 MeV. Similar analysis for Xi3/2 predicts its width to be not more than about 10 MeV. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons.

nucl-th↗

arXiv2003

Light cone nucleon wave function in the quark-soliton model

The light-cone wave function of the nucleon is calculated in the limit N_c -> infinity in the quark-soliton model inspired by the theory of the instanton vacuum of QCD. The technique of the finite time evolution operator is used in order to derive expressions for all components of the Fock vector describing the nucleon in the infinite momentum frame. It is shown that nucleon wave function for large N_c can be expressed in terms of the wave function of the discrete level in the self-consistent meson field and light cone wave functions of 1,2, etc mesons. The 3-quark components of the nucleon and Delta-resonance are estimated. Wave function of the nucleon appears to be positive in the whole region of x and it has rather small asymmetry. It differs strongly both from Chernyak-Zhitnitsky wave function and the asymptotic one. Large momentum transfer asymptotic of the electromagnetic and axial form factors is discussed.

hep-ph↗

arXiv2003

Lorentz invariance relations among parton distributions revisited

We revisit the derivation of the so-called Lorentz invariance relations between parton distributions. In the most important cases these relations involve twist-3 and transverse momentum dependent parton distributions. It is shown that these relations are violated if the path-ordered exponential is taken into account in the quark correlator.

hep-ph↗

arXiv2003

On photoexcitation of baryon antidecuplet

We show that the photoexcitation of the baryon antidecuplet, suggested by the soliton classification of low-lying baryons, is strongly suppressed on the proton target. The process occurs mostly on the neutron target. This qualitative prediction can be useful in identifying the non-exotic members of the antidecuplet in the known baryon spectrum. We also analyze the interrelation between photocouplings of various baryon multiplets in the soliton picture and in the nonrelativistic quark model.

hep-ph↗

arXiv2003

Genuine twist-3 contributions to the generalized parton distributions from instantons

The genuine twist-3 quark-gluon contributions to the Generalized Parton Distributions (GPDs) are estimated in the model of the instanton vacuum. These twist-3 effects are found to be parametrically suppressed relative to the ``kinematical'' twist-3 ones due to the small packing fraction of the instanton vacuum. We derive exact sum rules for the twist-3 GPDs.

hep-ph↗

arXiv2002

Spontaneously Broken Chiral Symmetry and Hard QCD Phenomena

These are the mini-proceedings of the workshop ``Spontaneously Broken Chiral Symmetry and Hard QCD Phenomena" held at the Physikzentrum Bad Honnef from July 15 to 19, 2002. Every author presents a summary of his talk. The transparencies of all speakers and further information on the workshop can be found on the website: http://www.tp2.ruhr-uni-bochum.de/hardreactions.html

hep-ph↗

arXiv2002

Novel hard semiexclusive processes and color singlet clusters in hadrons

Hard scattering to a three cluster final state is suggested as a method to probe configurations in hadrons containing small size color singlet cluster and a residual quark-gluon system of a finite mass. Examples of such processes include $e + N \to e+ p +M_X (Λ+M_X'), p+p \to p+p+M_X(p+Λ+M_X')$ where $M_X(M_X')$ could be a pion(kaon) or other state of finite mass which does not increase with momentum transfer ($Q^2$). We argue that different models of the nucleon may lead to very different qualitative predictions for the spectrum of states $M_X$. We find that in the pion model of nonperturbative $q \bar q$ sea in a nucleon the cross section of these reactions is comparable to the cross section of the corresponding two-body reaction. Studies of these reactions are feasible using both fixed target detectors (EVA at BNL, HERMES at DESY) and collider detectors with a good acceptance in the forward direction.

hep-ph↗

arXiv2002

Generalized parton distributions and strong forces inside nucleons and nuclei

We argue that generalized parton distributions (GPDs), accessible in hard exclusive processes, carry information about the spatial distribution of forces experienced by quarks and gluons inside hadrons. This way the measurements of hard exclusive processes open a possibility for direct "measurements" of strong forces in different parts of nucleons and nuclei. Also such studies open a venue for addressing questions of the properties of the quark (gluon) matter inside hadrons and nuclei. We give a simple example of relations between GPDs and properties of "nuclear matter" in finite nuclei.

hep-ph↗

arXiv2002

On "dual" parametrizations of generalized parton distributions

We propose a parametrization for the generalized parton distributions (GPDs) which is based on representation of parton distributions as an infinite series of t-channel exchanges. The entire generalized parton distribution is given as an infinite sum over contributions of generalized light-cone distribution amplitudes in the t-channel. We also discuss the relations of the lowest Mellin moments of GPDs to basic mechanical characteristics of the nucleon as a compound system.

hep-ph↗