The implications of one gluon exchange generated configuration mixing in the Chiral Quark Model (χQM gcm ) with SU(3) and axial U(1) symmetry breakings are discussed in the context of proton flavor and spin structure as well as the hyperon β-decay parameters. We find that χQM gcm with SU(3) symmetry breaking is able to give a satisfactory unified fit for spin and quark distribution functions, with the symmetry breaking parameters α = .4, β = .7 and the mixing angle φ = 20 o , both for NMC and the most recent E866 data. In particular, the agreement with data, in the case of G A /G V , ∆ 8 , F, D, f s and f 3 /f 8 , is quite striking.It is well known that the chiral quark model (χQM) [1,2,3] with SU(3) symmetry is not only able to give a fair explanation of "proton spin crisis" [4] but is also able to account for theū −d asymmetry [5,6,7] as well as the existence of significant strange quark contents in the nucleon when the asymmetric octet singlet couplings are taken into account [8]. Further, χQM with SU(3) symmetry is also able to provide fairly satisfactory explanation for various quark flavor contributions to the proton spin [9], baryon magnetic moments [3,9] as well as the absence of polarizations of the antiquark sea in the nucleon [10,11] . However, in the case of hyperon decay parameters the predictions of the χQM are not in tune with the data [12], for example, in comparison to the experimental numbers .21 and 2.17 the χQM with SU(3) symmetry predicts f 3 /f 8 and ∆ 3 /∆ 8 to be 1 3 and 5 3 respectively. It has been shown [10,13] that when SU(3) breaking effects are taken into consideration within χQM, the predictions of the χQM regarding the above mentioned ratios have much better overlap with the data.It is well known that constituent quark model (CQM) with one gluon mediated configuration mixing gives a fairly satisfactory explanation of host of 1 low energy hadronic matrix elements [14,15,16]. Besides providing a viable explanation for some of the difficult cases of photohelicity amplitudes [17], it is well known that one gluon generated configuration mixing is also able to provide viable explanation for neutron form factor [16,18], which cannot be accomodated without configuration mixing in CQM. Therefore, it becomes interesting to examine, within the χQM, the implications of one gluon mediated configuration mixing for flavor and spin structure of nucleon. In particular, we would like to examine the nucleon spin polarizations and various hyperon β-decay parameters, violation of Gottfried sum rule, strange quark content in the nucleon, fractions of quark flavor etc. in the χQM with configuration mixing (χQM gcm ), with and without symmetry breaking. Further, it would be interesting to examine whether a unified fit could be effected for spin polarization functions as well as quark ditribution functions or not.For the sake of readability as well to facilitate the discussion, we detail the essentails of χQM gcm discussed earlier by Harleen and Gupta [19]. The basic process, in the χQM, is the em...

Chiral quark model with configuration mixing and broken SU(3)×U(1) symmetry has been extended to include the contribution from cc fluctuations by considering broken SU(4) instead of SU(3). The implications of such a model have been studied for quark flavor and spin distribution functions corresponding to E866 and the NMC data. The predicted parameters regarding the charm spin distribution functions, for example, ∆c, There has been considerable interest in estimating the possible size of the intrinsic charm content of the nucleon [1][2][3][4][5]. Detailed investigations have been carried out regarding the size and implications of intrinsic charm contribution for nucleon [6] in a version of chiral quark model (χQM) [7][8][9][10][11][12][13] which is quite successful in giving a satisfactory explanation of "proton spin crisis" [14] including the violation of Gottfried sum rule [15][16][17]. Further, the same model is also able to account for the existence of significant strange quark contents [18,19] The successes of χQM in resolving the "proton spin crisis" and related issues strongly suggest that constituent quarks and the weakly interacting Goldstone bosons (GBs) provide the appropriate degrees of freedom in the nonperturbative regime of QCD. Thus the quantum fluctuations generated by broken chiral symmetry in χQM gcm should be able to provide a viable estimate of the heavier quark flavor, for example, cc, bb and tt. However, it is known that these flavor fluctuations are much suppressed in the case of bb and tt as compared to the cc because the intrinsic heavy quark contributions scale as 1/M 2 q , where M q is the mass of the heavy quark [1,30]. Therefore, regarding the intrinsic charm flavor content of the nucleon one should estimate only the contribution of cc fluctuations and for that one should be considering the extension of SU(3) symmetry in χQM to SU(4).The purpose of the present communication, on the one hand, is to extend χQM gcm with broken SU(3)×U(1) symmetry to broken SU(4)×U(1) symmetry. On the other hand, using the NMC [16] and the latest E866 data [17], we intend to study the implications of such a model for quark flavor and spin distribution functions, in particular the charm quark flavor and spin distribution functions.The details of χQM gcm within the SU(3) framework have already been discussed in Ref.[32], here we discuss the essentials of its extension to SU(4) χQM gcm . To begin with, the basic process in the χQM is the emission of a GB which further splits into qq pair, for example,wherein qq ′ pairs and q ′ constitute the "quark sea" with q ′ having opposite helicity as that of q. The effective Lagrangian describing interaction between quarks and the mesons in the SU(4) case iswhere g 15 is the coupling constant, 1

Magnetic moments of the low lying and charmed spin 1 2 + and spin 3 2 + baryons have been calculated in the SU(4) chiral constituent quark model (χCQM) by including the contribution from cc fluctuations. Explicit calculations have been carried out for the contribution coming from the valence quarks, "quark sea" polarizations and their orbital angular momentum. The implications of such a model have also been studied for magnetic moments of the low lying spin 3 2 + → 1 2 + and 1 2 + → 1 2 + transitions as well as the transitions involving charmed baryons. The predictions of χCQM not only give a satisfactory fit for the baryons where experimental data is available but also show improvement over the other models. In particular, for the case of µ(p), µ(Σ + ), µ(Ξ 0 ), µ(Λ), Coleman-Glashow sum rule for the low lying spin 1 2 + baryons and µ(∆ + ), µ(Ω − ) for the low lying spin 3 2 + baryons, we are able to achieve an excellent agreement with data. For the spin 1 2 + and spin 3 2 + charmed baryon magnetic moments, our results are consistent with the predictions of the QCD sum rules, Light Cone sum rules and Spectral sum rules. For the cases where "light" quarks dominate in the valence structure, the sea and orbital contributions are found to be fairly significant however, they cancel in the right direction to give the correct magnitude of the total magnetic moment. On the other hand, when there is an excess of "heavy" quarks, the contribution of the "quark sea" is almost negligible, for example, µ(Ω 0 c )

Baryon octet magnetic moments when calculated within the chiral quark model, incorporating the orbital angular momentum as well as the quark sea contribution through the Cheng-Li mechanism, not only show improvement over the non relativistic quark model results but also gives a non zero value for the right hand side of Coleman-Glashow sum rule. When effects due to spin-spin forces between constituent quarks as well as 'mass adjustments' due to confinement are added, it leads to an excellent fit for the case of p, Σ + , Ξ o and violation of Coleman-Glashow sum rule, whereas in almost all the other cases the results are within 5% of the data.The EMC measurements [1] in the deep inelastic scattering had shown that only a small fraction of the proton's spin is carried by the valence quarks. This 'unexpected' conclusion from the point of view of non relativistic quark model (NRQM), usually referred to as 'proton spin crisis', becomes all the more intriguing when it is realized that NRQM is able to give a reasonably good description of magnetic moments using the assumption that magnetic moments of quarks are proportional to the spin carried by them. This issue regarding spin and magnetic moments further becomes difficult to understand when it is realized that the magnetic moments of baryons receive contribution not only from the magnetic moments carried by the valence quarks but also from various complicated effects, such as, orbital excitations [2], sea quark polarization [3][4][5][6], effects of the chromodynamic spin-spin forces [7,8], effect of the confinement on quark masses [9], pion cloud contributions [10], loop corrections [11], relativistic and exchange current effects [12], etc.. In the absence of any consistent way to calculate these effects simultaneously, even couple of these, it is very difficult to know their relative contributions. However, the success of NRQM, when viewed in this context, suggests that the various effects mentioned above contribute in a manner where large part of these is mutually cancelled making the understanding of the magnetic moments alongwith 'spin crisis' all the more difficult. The problem regarding magnetic moments gets further complicated when one realizes that Coleman-Glashow sum rule [13] (CGSR), valid in large variety of models [14,15], is convincingly violated by the data [16]. For example, the CGSR for the baryon magnetic moments is given asExperimentally ∆CG = 0.49 ± 0.05 [16], clearly depicting the violation of CGSR by ten standard deviations. As ∆CG=0, in most of the calculations, obtaining ∆CG = 0 alongwith the octet magnetic moments as well as resolution for 'spin crisis' and related issues could perhaps provide vital clues for the dynamics as well as the appropriate degrees of freedom required for understanding some of the non-perturbative aspects of QCD. In this context, it is interesting to note that the chiral quark model (χQM) [4,17] with SU(3) symmetry is not only able to give a fair explanation of 'proton spin crisis' [1] but is also able to give a fair acc...

The effects of SU(3) symmetry breaking and configuration mixing have been investigated for the weak vector and axial-vector form factors in the chiral constituent quark model (χCQM) for the strangeness changing as well as strangeness conserving semi-leptonic octet baryon decays in the nonperturbative regime. The results are in good agreement with existing experimental data and also show improvement over other phenomenological models.

The magnetic moments of the negative parity octet resonances with spin 1 2 : N * (1535), N * (1650), Σ * (1620), and Ξ * (1690) have been calculated within the framework of the chiral constituent quark model. In this approach, the presence of the polarized qq pairs (or the meson cloud, in other words) is considered by using the Lagrangian for Goldstone boson emission from the constituent quarks. Further, the explicit contributions coming from the spin and orbital angular momentum, including the effects of the configurations mixing between the states with different spins, are obtained. The motivation for these calculations comes from the recent interest in experimental measurement of the magnetic moment of the S 11 (1535) resonance and of similar calculations being done within lattice quantum chromodynamics approaches. Our results can be compared with those expected to come from these sources.

The effects of "quark sea" in determining the flavor structure of the octet baryons have been investigated in the chiral constituent quark model (\chiCQM). The \chiCQM is able to qualitatively generate the requisite amount of quark sea and is also known to provide a satisfactory explanation of the proton spin and related issues in the nonperturbative regime. The Bjorken scaling variable x has been included phenomenologically in the sea quark distribution functions to understand its implications on the quark sea asymmetries like \bar d(x)-\bar (x), \bar d(x)/\bar u(x) and Gottfried integral for the octet baryons. The results strengthen the importance of quark sea at lower values of x.Comment: 7 pages, 2 figures, to appear in Phys. Rev.

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