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Register a new userThe $Omega$ and $Sigma^0$-$Lambda$ transition magnetic moments in QCD sum rules
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Shi-Lin Zhu
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The method of QCD sum rules in the presence of external elctromagnetic fields is used to calculate the $Omega$ magnetic moment $mu_{Omega^-}$ and $Sigma^0$-$Lambda$ transition magnetic moment $mu_{Sigma^0Lambda}$, with the susceptibilities obtained previously from the study of octet baryon magnetic moments. The results $mu_{Omega^-}=-1.92mu_N$ and $mu_{Sigma^0Lambda}=1.5mu_N$ are in good agreement with the recent experimental data.
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We calculate the on-shell $Sigma^0$-$Lambda$ mixing parameter $theta$ with the method of QCD sum rule. Our result is $theta (m^2_{Sigma^0}) =(-)(0.5pm 0.1)$MeV. The electromagnetic interaction is not included.
The $Sigma$--$Lambda$ mixing angle is calculated in framework of the QCD sum rules. We find that our prediction for the mixing angle is $(1.00pm 0.15)^0$ which is in good agreement with the quark model prediction, and approximately two times larger than the recent lattice QCD calculations.
Diagonal and transition magnetic moments of the negative parity, spin-1/2 heavy baryons are studied in framework of the light cone QCD sum rules. By constructing the sum rules for different Lorentz structures, the unwanted contributions coming from negative (positive) to positive (negative) parity transitions are removed. It is obtained that the magnetic moments of all baryons, except $Lambda_b^0$, $Sigma_c^+$ and $Xi_c^{prime +}$, are quite large. It is also found that the transition magnetic moments between neutral negative parity heavy $Xi_Q^{prime 0}$ and $Xi_Q^0$ baryons are very small. Magnetic moments of the $Sigma_Q to Lambda_Q$ and $ Xi_Q^{prime pm} to Xi_Q^pm$ transitions are quite large and can be measured in further experiments.
We evaluate the pion-nucleon and the pion-Delta sigma terms by employing the method of quantum chromodynamics (QCD) sum rules. The obtained value of the pion-nucleon sigma term is compatible with the larger values already anticipated by the recent calculations. It is also found that the pion-Delta sigma term is as large as the pion-nucleon sigma term.
We calculate the isoscalar axial-vector coupling constants of the Lambda hyperon using the method of QCD sum rules. A determination of these coupling constants reveals the individual contributions of the u, d and the s quarks to the spin content of Lambda. Our results for the light-quark contributions are in agreement with those from experiment assuming flavor SU(3). We also find that the flavor-SU(3)-breaking effects are small and the contributions from the u and the d quarks to the Lambda polarization are negatively polarized as in the flavor-SU(3) limit.
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