Magnetic Moments Of Hyperons Research Articles

Magnetic moment of hyperons in nuclear matter by using quark–meson coupling models

We calculate the magnetic moments of hyperons in dense nuclear matter by using relativistic quark models. Hyperons are treated as MIT bags, and the interactions are considered to be mediated by the exchange of scalar and vector mesons which are approximated as mean fields. Model dependence is investigated by using the quark–meson coupling model and the modified quark–meson coupling model; in the former the bag constant is independent of density and in the latter it depends on density. Both models give us the magnitudes of the magnetic moments increasing with density for most octet baryons. But there is a considerable model dependence in the values of the magnetic moments in dense medium. The magnetic moments at the nuclear saturation density calculated by the quark–meson coupling model are only a few percents larger than those in free space, but the magnetic moments from the modified quark–meson coupling model increase more than 10% for most hyperons. The correlations between the bag radius of hyperons and the magnetic moments of hyperons in dense matter are discussed.

Baryons in the SU(2) and SU(3) NJL model: A review of results

The semibosonized Nambu - Jona-Lasinio model in its SU(2) and SU(3) versions with scalar and pseudoscalar couplings is applied on the chiral circle to baryons (chiral quark soliton approach). The parameters of the model are fixed in the meson sector reproducing tf π , m π and m K . The constituent mass is chosen to be 420 MeV and no further parameter is adjusted. The baryons arise as a soliton of N c valence quarks coupled to the polarized Dirac sea. The calculations include 1 N c - rotational corrections and for the strange mass treated perturbatively the value m s = 180 MeV is used. The following agreement with the experimental data is obtained: With less than 15% deviation from experiment we obtain 〈 r 2 〉 c p , μ p , μ n , gA = g A (3), σ πN , g A (8), G p E ( q 2), G p M ( q 2), G n M ( q 2), E2 M1 , Δ- N-splitting, mass splittings of octet and decuplet baryons, magnetic moments of hyperons, isospin splittings of the octet and the Gottfried sum rule. With 30% deviation and at the borderline of exp. errors appear the electric neutron form factor and the other spin quantities g A (8) and Δu, Δd and Δs. Predictions are made for scalar form factor, strange form factors and tensor charges.

Constant-cutoff approach to magnetic moments of hyperons

We calculate the magnetic moments of hyperons in the simplified CHK model, with the stabilizing term proportional toe−2 omitted, based on the constant-cutoff limit of the cutoff quantization method developed by Balakrishna, Sanyuk, Schechter, and Subbaraman, which avoids the difficulties with the usual soliton boundary conditions pointed out by Iwasaki and Ohyama. Thus we show that there is qualitative agreement with the experimental values and the accuracy is similar to that obtained with the complete CHK model.

Chiral symmetry and the bound state approach to strangeness

We investigate within the framework of the kaon-soliton bound state model of hyperons the effects of introducing a linear combination of possible four-derivative stabilization terms allowed by general symmetry principles. We calculate the mass spectrum and magnetic moments of hyperons and see how they vary as a function of a new mixing parameter x. In all previous bound state model calculations this parameter was fixed at 1. We show that in some cases, a smaller value leads to improvement in the description of hyperon properties. We discuss empirical bounds coming from chiral perturbation theory for the possible values of x as well as the mesonic origin of the term it parametrizes.

Magnetic moments of hyperons in the simplified Skyrme model

We calculate the electromagnetic current in the simplified Skyrme model with the stabilizing term proportional to e −2 omitted, using the bound-state approach developed by Callan and Klebanov. The result for the electromagnetic current is used to calculate the magnetic moments of baryons, using a regularized version of the quantum stabilization method proposed by Mignaco and Wulck. Furthermore, we perform the numerical calculations of the magnetic moments of baryons and show that there is a qualitative agreement with the experimental values.

Vector mesons and magnetic moments of hyperons

We calculate hyperon magnetic moments by using the bound-state approach to the SU(3) Skyrme model. We analyze the role of the vector mesons as ω and ϱ meson in the calculation of the magnetic moment. Inclusion of an ω vector meson, instead of the Skyrme term, shows a net improvement of the nonstrange part of the isoscalar current. Taking account of the ϱ vector meson, although only treated approximately in the SU(2) sector, does not give a meaningful improvement in isoscalar or isovector current, if we fix the physical input of the model to fit the hyperon masses. Importance of the heavy vector mesons is argued, not only in the hyperfine mass splitting but also in the magnetic moment. It is also argued that the treatment of the gauged Wess-Zumino action in the SU(2) sector is crucial in reproducing the experimental results.

Magnetic moments of hyperons in the bound state approach to the skyrme model

We construct the electromagnetic current in the bound state approach to the Skyrme model using the Callan-Klebanov ansatz. The current is used to calculate the magnetic moments of the baryons for the case of massless pions. The agreement of the magnetic moments in the bound state approach with the experimental magnetic moments is qualitatively satisfying. We disagree with previous work by Nyman and Riska.

Magnetic moments of the hyperons in the topological soliton model

The magnetic moments of the hyperons are calculated in a model where the hyperons are described as bound states of a non-strange topological soliton and K-mesons. The calculated values of the magnetic moments of the stable hyperons are within 30% of the empirical values. The predicted magnetic moments of the hyperon resonances are compared to the usual SU(6) quark-model values.

Algebra of currents and the magnetic moments of hyperons

Using equal time commutation relations of the strangeness-changing axial-vector “charges” with the isoscalar and isovector electromagnetic current densities, the magnetic moments of Σ + and Λ have been calculated in terms of the kaon photoproduction amplitudes, which are evaluated using low lying baryon resonant states. The results agree very well with the experimental values.

Magnetic moments of hyperons

Magnetic moments of hyperons

Anomalous Magnetic Moments of Hyperons and Mirror Theorem

According to the theory of d'Espagnat and Prentki the anomalous magnetic moments of hyperons are calculated in the lowest-order perturbation approximation. It is further shown that their charge-independent interaction Hamiltonian leads to the mirror theorem for the anomalous magnetic moments of baryons (and of K mesons) without use of perturbation approximation. Finally the anomalous magnetic moments of SIGMA hyperons determined from the mass differences of SIGMA and the mirror theorem are compared with the perturbation results. (auth)