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We report on a calculation of higher electromagnetic multipole moments of baryons in a non-covariant quark model approach. The employed method is based on the underlying spin-flavor symmetry of the strong interaction and its breaking.We present results on magnetic octupole moments of decuplet baryons and discuss their implications.
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Quadrupole moments of decuplet baryons and the octet-decuplet transition quadrupole moments are calculated using Morpurgos general QCD parameterization method. Certain relations among the decuplet and the octet to decuplet transition quadrupole moments are derived. These can be used to predict the $Delta$ quadrupole moments which are difficult to measure.
We calculate the charge quadrupole and magnetic octupole moments of baryons using a group theoretical approach based on broken SU(6) spin-flavor symmetry. The latter is an approximate symmetry of the QCD Lagrangian which becomes exact in the large color N_c limit. Spin-flavor symmetry breaking is induced by one-, two-, and three-quark terms in the electromagnetic current operator. Two- and three-quark currents provide the leading contributions for higher multipole moments, despite being of higher order in an 1/N_c expansion. Our formalism leads to relations between N --> N* transition multipole moments and nucleon ground state properties. We compare our results to experimental quadrupole and octupole transition moments extracted from measured helicity amplitudes.
We present a comparative study of the charmed baryon$-$nucleon interaction based on different theoretical approaches. For this purpose, we make use of i) a constituent quark model tuned in the light-flavor baryon$-$baryon interaction and the hadron spectra, ii) existing results in the literature based both on hadronic and quark-level descriptions, iii) (2+1)-flavor lattice QCD results of the HAL QCD Collaboration at unphysical pion masses and their effective field theory extrapolation to the physical pion mass. There is a general qualitative agreement among the different available approaches to the charmed baryon$-$nucleon interaction. Different from hadronic models based on one-boson exchange potentials, quark$-$model based results point to soft interactions without two-body bound states. They also support a negligible channel coupling, due either to tensor forces or to transitions between different physical channels, $Lambda_c N - Sigma_c N$. Short-range gluon and quark-exchange dynamics generate a slightly larger repulsion in the $^1S_0$ than in the $^3S_1$ $Lambda_c N$ partial wave. A similar asymmetry between the attraction in the two $S$ waves of the $Lambda_c N$ interaction also appears in hadronic approaches. A comparative detailed study of Pauli suppressed partial waves, as the $^1S_0 (I=1/2)$ and $^3S_1 (I=3/2)$ $Sigma_c N$ channels, would help to disentangle the short-range dynamics of two-baryon systems containing heavy flavors. The possible existence of charmed hypernuclei is discussed.
We use a consistent SU(6) extension of the meson-baryon chiral Lagrangian within a coupled channel unitary approach in order to calculate the T-matrix for meson-baryon scattering in s-wave. The building blocks of the scheme are the pion and nucleon octets, the rho nonet and the Delta decuplet. We identify poles in this unitary T-matrix and interpret them as resonances. We study here the non exotic sectors with strangeness S=0,-1,-2,-3 and spin J=1/2, 3/2 and 5/2. Many of the poles generated can be associated with known N, Delta, Sigma, Lambda and Xi resonances with negative parity. We show that most of the low-lying three and four star odd parity baryon resonances with spin 1/2 and 3/2 can be related to multiplets of the spin-flavor symmetry group SU(6). This study allows us to predict the spin-parity of the Xi(1620), Xi(1690), Xi(1950), Xi(2250), Omega(2250) and Omega(2380) resonances, which have not been determined experimentally yet.
We propose a novel approach to study a possible role of the quantum chromodynamics vacuum in nuclear and hadron physics. Our proposal is essentially to introduce a candidate of the QCD vacuum through a gluon background field and calculate physical quantities as a function of the background field. In the present work we adopt the Copenhagen (spaghetti) vacuum. As a first application of the our approach, we investigate the effects of the Copenhagen vacuum on the ground-state baryon masses. We find that the baryon mass does depend on a parameter that characterizes the Copenhagen vacuum and satisfies the Gell-Mann-Okubo mass relation for the baryon octet. We also estimate the value of the parameter and discuss the chiral invariant nucleon mass in our framework.
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