Pentaquarks in chiral soliton models

Abstract

The spectra of pentaquarks, some of them being observed recently, are discussed within topological soliton model and compared with simplified quark picture. Results obtained within chiral soliton model depend to some extent on the quantization scheme: rigid rotator, soft rotator, or bound state model. The similarity of spectra of baryon resonances obtained within quark model and chiral soliton model is pointed out, although certain differences take place as well, which require careful interpretation. In particular, considerable variation of the strange antiquark mass in different SU (3) multiplets of pentaquarks is required to fit their spectra obtained from chiral solitons. Certain difference of masses of "good" and "bad" diquarks is required as well, in qualitative agreement with previously made estimates. The partners of exotic states with different values of spin which belong to higher SU (3) multiplets, have the energy considerably higher than states with lowest spin, and this could be a point where the difference from simple quark models is striking. The antiflavor excitation energies for multibaryons are estimated as well, and binding energies of Θ-hypernuclei and anticharm (antibeauty) hypernuclei are presented for several baryon numbers. Some deficiencies in the argumentation against validity of the chiral soliton approach and/or SU (3) quantization models, existing in the literature, are pointed out.

Baryon spectrum in largeNcchiral soliton and in quark models

“…in [32]. For large N generalization of the octet, the decuplet of baryons and for the Θ + baryon this method has been used recently in [8] to calculate strangeness contents of these baryons. For exotic baryon multiplets, "antidecuplet", "{27}"-and "{35}"-plets (shown in Fig.…”

“…For arbitrary (odd) number of colors the hypercharge is connected with strangeness by relation Y = S + NB/3, see e.g. [2,15,8] (we omit the index c in N c in most of formulas and in Tables 1,2). It is more convenient therefore to use for the B = 1 case the quantity Y ′ = S + 1, as we do in Tables and in Fig.…”

“…It is shown as well that the partners of baryon resonances with different J P predicted within quark models are present also in the CSA, although they have usually higher energy. Some of these questions have been addressed in talks [8], and here we add more rigour to this consideration.…”

“…Although there was intensive discussion of connections of the rigid rotator model (RRM) and the bound state model (BSM) in the literature, mainly in the large N c limit [15,16,17,18,19,20,21,22], explicit analytical calculations of observable quantities at arbitrary N c were lacking still, except several cases [8,22], [21]. The rotationvibration approach (RVA) described in [22,23] and references in these papers, includes both rotational (zero modes) and vibrational degrees of freedom of solitons and is generalization of both RRM and BSM, which appear therefore as particular variants of RVA when certain degrees of freedom are frozen (see also discussion in Section 3)…”

“…Consideration of baryon states in the present paper is relevant independently on particular values of masses, widths and other properties of exotic baryon states measured experimentally. A detailed discussion of theoretical predictions of these states can be found in [7,8,9,10,11] 2 Some analogy with nuclei can be noted: two-, three-, etc. nucleon clusters play an important role in the structure of heavy nuclei, however, it is not possible to evaluate their properties from those of deuteron, helium etc., only.…”