Chiral Soliton Research Articles

The Experimental Search for Pentaquark

The existence of an anti-decuplet of pentaquark particles has been predicted some year ago within the chiral soliton model. In the last year, several experimental groups have reported evidence for a S=+1 baryon resonance, with mass ranging from 1.52 and 1.55 GeV and width less than 25 MeV, by looking at the invariant mass of the $K N$ system. This resonance, has been identified with the lowest mass of the anti-decuplet, the $\Theta^+$. At the same time, there are a number of experiment, mostly at high energies, that report null results. An overview of the experimental results so far obtained will be given here together with a review of the second generation experiments currently ongoing and planned at Jefferson Lab Hall B.

Today’s view on strangeness

There are several different experimental indications, such as the pion-nucleon sigma term and polarized deep-inelastic scattering, which suggest that the nucleon wave function contains a hidden s bar s component. This is expected in chiral soliton models, which also predicted the existence of new exotic baryons that may recently have been observed. Another hint of hidden strangeness in the nucleon is provided by copious phi production in various N bar N annihilation channels, which may be due to evasions of the Okubo-Zweig-Iizuka rule. One way to probe the possible polarization of hidden s bar s pairs in the nucleon may be via Lambda polarization in deep-inelastic scattering.

Nuclear matter in the chiral quark soliton model(Quantum Field Theories : Fundamental Problems and Applications)

Nuclear matter in the chiral quark soliton model(Quantum Field Theories : Fundamental Problems and Applications)

Pentaquark search at Jefferson Laboratory

The search for baryon resonances with the strangeness quantum number S=+1 that cannot be formed by three quarks has a long history. In the last year, several experimental groups have reported evidence for a S=+1 baryon state, with mass ranging from 1.52 and 1.55 GeV and width less than 25 MeV, by looking at the invariant mass of theKN system. This resonance has been identified with the lowest mass, the Θ+, of the anti-decuplet of pentaquark particles predicted some year ago within the chiral soliton model. At the same time there are a number of experiment, mostly at high energies, that report null results.

Transversity distribution in spin asymmetries in semi-inclusive DIS and in the Drell-Yan process

A review is given on single spin asymmetries in deep inelastic semi-inclusive scattering (SIDIS) and their possible theoretical understanding in the framework of QCD-induced factorization approach, wherefore predictions for transversity from the chiral quark soliton model are used. Arising difficulties to interpret most recent SIDIS data, and the possibility to access the transversity distribution in the Drell-Yan process are discussed.

Flavored exotic multibaryons and hypernuclei in topological soliton models

The energies of baryon states with positive strangeness, or anti-charm (-beauty) are estimated in chiral soliton approach, in the "rigid oscillator" version of the bound state soliton model proposed by Klebanov and Westerberg. Positive strangeness states can appear as relatively narrow nuclear levels (Theta-hypernuclei), the states with heavy anti-flavors can be bound with respect to strong interactions in the original Skyrme variant of the model (SK4 variant). The binding energies of anti-flavored states are estimated also in the variant of the model with 6-th order term in chiral derivatives in the lagrangian as solitons stabilizer (SK6 variant). The latter variant is less attractive, and nuclear states with anti-charm or anti-beauty can be unstable relative to strong interactions. The chances to get bound hypernuclei with heavy antiflavors are greater within "nuclear variant" of the model with rescaled model parameter (Skyrme constant e or e' decreased by ~30%) which is expected to be valid for baryon numbers greater than B ~10. The rational map approximation is used to describe multiskyrmions with baryon number up to ~30 and to calculate the quantities necessary for their quantization (moments of inertia, sigma-term, etc.).

35-plet baryons from chiral soliton models

We investigate the 35-plet baryons from the chiral soliton models. We find that the coupling constant for the decay of 35-plet baryons with spin 3/2 to the decuplet baryons is surprisingly small, but that for the decay to 27-plet baryons with spin 3/2 is larger. We give all the masses and widths of 35-plet baryons with spin 5/2 and suggest candidates for all nonexotic members from the available particle listings. We also focus on $\Delta_{5/2}$ and $\Theta_2$, which are the lightest two baryons of 35-plet with spin 5/2 and with simplest minimal pentaquark configurations. Calculations show that $\Gamma_{\Delta_{5/2}}<$380 MeV, compared with the results from SU(2) Skyrme Model ($\Gamma_{\Delta_{5/2}}>$800 MeV), and $\Gamma_{\Theta_{2}}<100$ MeV if we assume that their widths are dominated by two-body decay and that $\Theta^+$ has a width $\Gamma_{\Theta^+}<25$ MeV.

Generalized parton distributions, nucleon form factors, and large‐t processes*

AbstractThe connection of generalized parton distributions (GPDs) to processes at large momentum transfer (high‐t), and the links between GPDs and elastic nucleon form factors are discussed here. These links, in the form of sum rules, represent powerful constraints on parametrizations of GPDs. A Regge parametrization for the GPDs at small‐t, which is surprisingly observed from the chiral quark soliton model results, is extended to the large‐t region and it is found to catch the basic features of proton and neutron electromagnetic form factor data. It is furthermore discussed how these GPDs at large‐t enter into two‐photon exchange processes and resolve the discrepancy between Rosenbluth and polarization experiments of elastic electron nucleon scattering.

Parity of antidecuplet baryons reexamined from chiral soliton models

We recalculate masses and widths of anti-decuplet baryons in the case of positive parity from chiral soliton models, provided that the member $\Xi_{3/2}$ of the anti-decuplet has a mass 1.86 GeV as reported recently. Calculations show that there are no convincing candidates for the nonexotic members of the anti-decuplet available in the baryon listings. Up to the leading order of $m_s$ and 1/$N_c$, the width formula for the decay of the anti-decuplet baryons to the octet depends only on SU(3) symmetry model-independently, except the coupling constant. Similarly we give a width formula for the decay of negative parity baryons belong to certain SU(3) baryon multiplet by pure symmetry consideration. By this formula, we find that if we have an anti-decuplet with negative parity and that the masses are the same as those given by chiral soltion models, the identification of N(1650) as $N_{\bar{10}}$ are inconsistent with experiments for $N(1650)\to N\pi$ while the widths agree with other two decay channels involving strangeness. And $\Sigma(1750)$ seems to be a reasonable candidate for $\Sigma_{\bar{10}}$.

Skyrmions and pentaquarks in the quark–hadron continuity perspective

We argue that in the color-flavor-locking (CFL) superconducting phase classical soliton solutions can exist, whose excitations should be interpreted as states formed by a quark (or an antiquark) and condensed diquarks. This finding extends the picture of quark–hadron continuity showing the existence of a region, intermediate between the CFL and the hypernuclear phase, where chiral solitons and Nambu–Goldstone bosons can exist. We derive an expression of the soliton mass in terms of the QCD coupling, gs, and the Nambu Goldstone boson parameters. From the quark–hadron continuity we can draw an argument in favor of the interpretation of the Θ+(1540) particle in terms of a strange antiquark and two highly correlated ud pairs (diquarks).

Pion-nucleon scattering relations at next-to-leading order in1/Nc

We obtain relations between partial-wave amplitudes for pi-N-->pi-N and pi-N-->pi-Delta directly from large N_c QCD. While linear relations among certain amplitudes holding at leading order (LO) in 1/N_c were derived in the context of chiral soliton models two decades ago, the present work employs a fully model-independent framework based on consistency with the large N_c expansion. At LO we reproduce the soliton model results; however, this method allows for systematic corrections. At next-to-leading order (NLO), most relations require additional unknown functions beyond those appearing at leading order (LO) and thus have little additional predictive power. However, three NLO relations for the pi-N-->pi-Delta reaction are independent of unknown functions and make predictions accurate at this order. The amplitudes relevant to two of these relations were previously extracted from experiment. These relations describe experiment dramatically better than their LO counterparts.

Chiral soliton model for arbitrary colors and flavors

The semiclassical quantization of the chiral soliton model is studied for an arbitrary number of colors and flavors. The quantum numbers of the baryons in the soliton model are derived and are shown to agree with those in the constituent quark model for normal as well as exotic baryons. The general analysis elucidates the correct definition of exoticness for the three-flavor case, and allows one to interpret the soliton state in terms of quark model variables. The quantum numbers of all the allowed soliton states for the physically relevant case of three flavors are derived.

BrokenSU(3)antidecuplet forΘ+andΞ3/2

If the narrow exotic baryon resonances $\Theta^+(1540)$ and $\Xi_{{3/2}(1862)$ are members of the $J^P = {1/2}1/2^+$ antidecuplet with $N^*(1710)$, the octet-antidecuplet mixing is required not only by the mass spectrum but also by the decay pattern of $N^*(1710)$. This casts doubt on validity of the $\Theta^+$ mass prediciton by the chiral soliton model. While all pieces of the existing experimental information point to a small octet-antidecuplet mixing, the magnitude of mixing required by the mass spectrum is not consistent with the value needed to account for the hadronic decay rates. The discrepancy is not resolved even after the large experimental uncertainty is taken into consideration. We fail to find an alternative SU(3) assignment even with different spin-parity assignment.

θ+baryon in soliton models: LargeNcQCD and the validity of rigid-rotor quantization

A light collective theta+ baryon state (with strangeness +1) was predicted via rigid-rotor collective quantization of SU(3) chiral soliton models. This paper explores the validity of this treatment. A number of rather general analyses suggest that predictions of exotic baryon properties based on this approximation do not follow from large Nc QCD. These include an analysis of the baryon's width, a comparison of the predictions with general large Nc consistency conditions of the Gervais-Sakita-Dashen-Manohar type; an application of the technique to QCD in the limit where the quarks are heavy; a comparison of this method with the vibration approach of Callan and Klebanov; and the 1/Nc scaling of the excitation energy. It is suggested that the origin of the problem lies in an implicit assumption in the that the collective motion is orthogonal to vibrational motion. While true for non-exotic motion, the Wess-Zumino term induces mixing at leading order between collective and vibrational motion with exotic quantum numbers. This suggests that successful phenomenological predictions of theta+ properties based on rigid-rotor quantization were accidental.

Moments of inertia, nucleon axial-vector coupling, the8,10, and273/2mass spectrums and the higher SU(3)frepresentation mass splittings in the Skyrme model

The broad importance of a recent experimental discovery of pentaquarks requires more theoretical insight into the structure of higher representation multiplets. The nucleon axial-vector coupling, moments of inertia, the {\bf 8}, {\bf 10}, $\bar{\bf 10}$, and ${\bf 27}_{3/2}$ absolute mass spectra and the higher SU(3)$_f$ representation mass splittings for the multiplets ${\bf 8}$, ${\bf 10}$, $\bar{\bf 10}$, ${\bf 27}$, ${\bf 35}$, $\bar{\bf 35}$, and $\bf 64$ are computed in the framework of the minimal ${\rm SU(3)_f}$ extended Skyrme model by using only one free parameter, i.e., the Skyrme charge $e$. The analysis presented in this paper represents simple and clear theoretical estimates, obtained without using any experimental results for higher ($\bar{\bf 10}$,...) multiplets. The obtained results are in good agreement with other chiral soliton model approaches that more extensively use experimental results as inputs.

Exotic baryons and monopole excitations in a chiral soliton model

We compute the spectra of exotic pentaquarks and monopole excitations of the low--lying ${1/2}^+$ and ${3/2}^+$ baryons in a chiral soliton model. Once the low--lying baryon properties are fit, the other states are predicted without any more adjustable parameters. This approach naturally leads to a scenario in which the mass spectrum of the next to lowest--lying $J^\pi={1/2}^+$ states is fairly well approximated by the ideal mixing pattern of the $\mathbf{8}\oplus\bar{\mathbf{10}}$ representation of flavor SU(3). We compare our results to predictions obtained in other pictures for pentaquarks and speculate about the spin--parity assignment for $\Xi(1690)$ and $\Xi(1950)$

πN sigma term and chiral-odd twist-3 distribution function e(x) of the nucleon in the chiral quark soliton model

The isosinglet combination of the chiral-odd twist-3 distribution function $e^u(x)+e^d(x)$ of the nucleon has outstanding properties that its first moment is proportional to the well-known $\pi N$ sigma-term and that it contains a $\delta$-function singularity at $x=0$. These two features are inseparably connected in that the above sum rule would be violated, if there is no such a singularity in $e^u(x)+e^d(x)$. Very recently, we found that the physical origin of this $\delta$-function singularity can be traced back to the long-range quark-quark correlation of scalar type, which signals the spontaneous chiral symmetry breaking of the QCD vacuum. The main purpose of the present paper is to give complete theoretical predictions for the chiral-odd twist-3 distribution function $e^a(x)$ of each flavor $a$ on the basis of the chiral quark soliton model, without recourse to the derivative expansion type approximation. These theoretical predictions are then compared with the empirical information extracted from the CLAS data of the semi-inclusive DIS processes by assuming the Collins mechanism only. A good agreement with the CLAS data is indicative of a sizable violation of the $\pi N$ sigma-term sum rule, or equivalently, the existence of a $\delta$-function singularity in $e^u(x) + e^d(x)$.

Transversity distribution function in hard scatteringof polarized protons and antiprotons in the PAX experiment

Estimates are given for the double spin asymmetry in lepton-pair production from collisions of transversely polarized protons and antiprotons for the kinematics of the recently proposed PAX experiment at GSI on the basis of predictions for the transversity distribution from the chiral quark soliton model.

Degeneracy of the quarks, shell structure in the chiral soliton

We obtain multi-winding number configurations with discrete symmetries in the chiral quark soliton model using the rational map ansatz. The solutions exhibit degenerate bound spectra of the quark orbits depending on the background of pion field configurations. It is shown that resultant baryon densities inherit the same discrete symmetries as the chiral fields. Evaluating the radial component of the baryon density, shell-like structure of the valence quark spectra is also observed.

27-plet baryons from chiral soliton models

We use the perturbation method to calculate the masses and widths for 27-plet baryons with spin 3/2 from chiral soliton models. According to the masses and quantum numbers, we find all the candidates for non-exotic members of 27-plet. The calculation of the widths shows that these candidates manifest an approximate symmetry of the 27 representation of the SU(3) group, and the quantum numbers of $\Xi(1950)$ seem to be $I(J^P)={1/2}({3/2}^+)$. Up to leading order of the strange quark mass, we find that the exotic members have widths much larger than those of the anti-decuplet members.