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DOI:https://doi.org/10.1103/PhysRevD.67.039901

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... So the problem of determination of the mixing angle requires the calculation of the theoretical part of the correlation function, for which the expressions of the interpolating currents are needed. According to the SU(3) f classification the interpolating currents for the unmixed Λ 0 and Σ 0 are chosen as [10,11], ...

... GeV. It follows from the analysis of the mass sum rules that in order to reproduce the experimental values of the masses of the Σ and Λ baryons, the continuum threshold s 0 should lie in the range 2.5 GeV 2 ≤ s 0 ≤ 3.2 GeV 2 [10,11]. Moreover, the working region of the Borel mass parameter should be such that, the results for the Σ-Λ mixing angle should exhibit good stability with respect to the variation of M 2 at fixed values of s 0 . ...

The Σ-Λ mixing angle is calculated in framework of the QCD sum rules by using the general form of the interpolating current. We find that our prediction for the mixing angle is (1.15 ± 0.05)0. A comparison of our result with the predictions of the quark model, chiral perturbation theory, and lattice QCD approach, and also with the results of the QCD sum rules method existing in literature, is presented.

Recently the observation of a new pentaquark state, the hidden-charmed strange Pcs(4459)0, was reported by the LHCb Collaboration. The spin-parity quantum numbers of this state were not determined as a result of insufficient statistics. To shed light on its quantum numbers, we investigate its decay, Pcs(4459)0→J/ψΛ, the mode that this state has been observed, within the QCD sum rule framework. We obtain the width of this decay assigning the spin-parity quantum numbers of the Pcs(4459)0 state as JP=12− and its substructure as diquark-diquark-antiquark. To this end, we first calculate the strong coupling constants defining the considered decay and then use them in the width calculations. The obtained width is consistent with the experimental observation, confirming the quantum numbers JP=12− and compact pentaquark nature for the Pcs(4459)0 state.

The quark parts of the gravitational form factors of hyperons are calculated by means of the light-cone QCD sum rule. In the calculations, the distribution amplitudes (DAs) of Σ, Ξ, and Λ together with the general forms of their interpolating currents as well as the quark part of the energy-momentum tensor current are used. These form factors can provide information on their mass and distributions of the angular momentum, energy and pressure inside the hyperons. It is obtained that the Q2 dependencies of the hyperon gravitational form factors are nicely characterized by a multipole fit function. Using the fits of these form factors, some mechanical properties such as the mechanical radius of the hyperons and the pressure and energy distributions at the center of these particles are obtained. The obtained results can help us in better understanding of the internal structures of these baryons and the QCD as theory of the strong interaction.

The quadrupole moments of ground state baryons are discussed inn the framework of the 1/Nc expansion of QCD, where Nc is the number of color charges. Theoretical expressions are first provided assuming an exact SU(3) flavor symmetry, and then the effects of symmetry breaking are accounted for to linear order. The rather scarce experimental information available does not allow a detailed comparison between theory and experiment, so the free parameters in the approach are not determined. Instead, some useful new relations among quadrupole moments, valid even in the presence of first-order symmetry breaking, are provided. The overall predictions of the 1/Nc expansion are quite enlightening.

We calculate the magnetic moment of the recently observed
Θ+ pentaquark state in the framework of the light cone
QCD sum rules using the photon distribution amplitudes. We find that
μΘ+=(0.12±0.06)μN,
which is quite small. We also compare our result with predictions of
other groups.

New relations between the Borel sum rules in QCD for the magnetic moments of the {sigma}{sup 0} and {lambda} hyperons are derived. It is shown that, on the basis of the sum rule for the magnetic moment of the {sigma}{sup 0} hyperon, one can directly obtain the corresponding sum rule for the magnetic moment of the {lambda} hyperon, and vice versa, as well as the corresponding sum rule for the {sigma}{sup 0} {yields} {lambda}{gamma} transition.

The magnetic moments of spin (1/2){sup +} and spin (3/2){sup +} charmed baryons have been calculated in chiral constituent quark model (CQM). The effects of configuration mixing and quark masses have also been investigated. The results are not only in good agreement with existing experimental data but also show improvement over other phenomenological models.

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 (chiCQM) 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 chiCQM 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 mu(p), mu(Sigma+), mu(Xi0), mu(Lambda), Coleman-Glashow sum rule for the low lying spin (1)/(2)+ baryons and mu(Delta+), mu(Omega-) 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, mu(Omegac0), mu(Lambdac+), mu(Xic+), mu(Xic0), mu(Omegacc+), mu(Omega-), mu(Omegac*0), mu(Omegacc*+), and mu(Omegaccc*++). The effects of configuration mixing and quark masses have also been investigated.

The magnetic moments of heavy XiQ baryons containing a single charm or bottom quark are calculated in the framework of the light cone QCD sum rules method. A comparison of our results with the predictions of other approaches, such as relativistic and nonrelativistic quark models, the hypercentral model, chiral perturbation theory, and soliton and skyrmion models, is presented.

We present the light-cone QCD sum rules up to twist 6 for the electromagnetic form factors of the Λ baryon. To estimate the magnetic moment of the baryon, the magnetic form factor is fitted by the dipole formula. The numerical
value of our estimation is μ
Λ
=−(0.64±0.04)μ
N
, which is in accordance with the experimental data and the existing theoretical results. We find that it is twist 4 but not
the leading twist distribution amplitudes that dominate the results.

The electromagnetic form factors of octet baryons are estimated within light
cone QCD sum rules method, using the most general form of the interpolating
current for baryons. A comparison of our predictions on the magnetic dipole and
electric form factors with the results of other approaches is performed.

We examine the radiative Δ→γN transition at the real photon point Q2=0 using the framework of light-cone QCD sum rules. In particular, the sum rules for the transition form factors GM(0) and REM are determined up to twist 4. The result for GM(0) agrees with experiment within 10% accuracy. The agreement for REM is also reasonable. In addition, we derive new light-cone sum rules for the magnetic moments of nucleons, with a complete account of twist-4 corrections based on a recent reanalysis of photon distribution amplitudes.

The magnetic moment μ of the ρ meson is studied in QCD light cone
sum rules, and it is found that μ=(2.3±0.5), in units of
e/2mρ. A comparison of our result on the magnetic moment
of the ρ meson with the predictions of the other approaches is
presented.

Based on QCD conformal partial wave expansion to leading order conformal spin accuracy, we present the light-cone distribution amplitudes (DAs) of Σ and Λ baryons up to twist 6. It is concluded that fourteen independent DAs are needed to describe the valence three-quark states of the baryons at small transverse separations. The nonperturbative parameters relevant to the DAs are determined within the framework of QCD sum rule method. With the obtained DAs, a simple investigation on the electromagnetic form factors of these baryons are given. The magnetic moments of the baryons are estimated by fitting the magnetic form factor with the dipole formula.

The baryon magnetic and transition magnetic moments are computed in heavy baryon chiral perturbation theory in the large-N_c limit, where N_c is the number of colors. One-loop nonanalytic corrections of orders m_q^{1/2} and m_q ln m_q are incorporated into the analysis, where contributions of both intermediate octet and decuplet baryon states are explicitly included. Expressions are obtained in the limit of vanishing baryon mass differences and compared with the current experimental data. Furthermore, a comparison with conventional heavy baryon chiral perturbation theory is carried out for three light quarks flavors and at the physical value N_c=3. Comment: RevTex4, 36 pages, 2 eps figures; corrected typos; results agree with the ones of Ref. [26]

The magnetic dipole moments of the light tensor mesons $f_2$, $a_2$ and
strange $K_2^{\ast 0} (1430)$ tensor meson are calculated in the framework of
the light cone QCD sum rules. It is observed that the values of the magnetic
dipole moment for the charged tensor particles are considerably different from
zero. These values are very close to zero for the light neutral $f_2$ and $a_2$
tensor mesons, while it has a small nonzero value for the neutral strange
$K_2^{\ast 0} (1430)$ tensor meson.

We investigate the electromagnetic form factors of the (rho) meson in light cone QCD sum rules. We find that the ratio of the magnetic and charge form factors is larger than two at all values of Q^2, (Q^2 >= 0.5 GeV^2). The values of the individual form factors at fixed values of Q^2 predicted by the light cone QCD sum rules are quite different compared to the results of other approaches. These results can be checked in future, when more precise data on (rho) meson form factors is available. Comment: 12 pages, 6 figures, LaTeX formatted

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