Roper resonances in chiral quark models

We derive a method to calculate the multi-channel K matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate pion scattering amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data is achieved if in addition to the elastic channel we include the $\pi\Delta$ and $\sigma N$ ($\sigma\Delta$) channels where the $\sigma$-meson models the correlated two-pion decay. We solve the integral equation for the K matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the $\Delta(1232)$ and the N(1440) resonances compared to the bare quark values.Comment: 17 pages, 7 figure

Eta and kaon production in a chiral quark model

We apply a coupled-channel formalism incorporating quasi-bound quark-model states to calculate pion scattering into eta N, K Lambda and K Sigma channels, as well eta p, eta n, K+Lambda, and K0Sigma+ photo-production processes. The meson-baryon and photon-baryon vertices are determined in a SU(3) version of the Cloudy Bag Model. Our model predicts sizable amplitudes in the P11, P13, P33 and S11 partial waves in agreement with the latest MAID isobar model and the recent partial-wave analyses of the Bonn-Gatchina group. We are able to give a quark-model explanation for the apparent resonance at 1685 MeV in the eta n channel.Comment: 14 pages, 12 figures, to appear in EPJ

A chiral quark model for meson electro-production in the region of D-wave resonances

The meson scattering and electroproduction amplitudes in the D13, D33 and D15 partial waves are calculated in a coupled-channel formalism incorporating quasi-bound quark-model states, extending our previous studies of the P11, P33 and S11 partial waves. The vertices of the baryon-meson interaction including the s- and d-wave pions and $\rho$-mesons, the s-wave $\eta$-meson, and the $s$- and p-wave $\sigma$-mesons are determined in the Cloudy Bag Model, with some changes of the parameters to reproduce the widths of the resonances. The helicity amplitudes and the electroproduction amplitudes exhibit consistent behavior in all channels but tend to be too weak compared to the experiment. We discuss possible origins of this discrepancy which arises also in the constituent quark model calculations.Comment: 11 pages, 11 figures, accepted for publication in EPJ

Solitons in nonlocal chiral quark models

Properties of hedgehog solitons in a chiral quark model with nonlocal regulators are described. We discuss the formation of the hedgehog soliton, the quantization of the baryon number, the energetic stability, the gauging and construction of Noether currents with help of path-ordered P-exponents, and the evaluation of observables. The issue of nonlocality is thoroughly discussed, with a focus on contributions to observables related to the Noether currents. It is shown that with typical model parameters the solitons are not far from the weak nonlocality limit. The methods developed are applicable to solitons in models with separable nonlocal four-fermion interactions.Comment: 42 pages, 8 figures, a new section presenting the results with the chiral-circle constrain

Razmatranje Roperove rezonancije

Different approaches to the Roper resonance are reviewed, revealing the multiple facet of this state and the need for some crucial experiments.Dajemo pregled nekoliko mogućih tumačenja Roperove rezonancije, te ukazujemo na složenost tog stanja, kao i na potrebu za novim mjerenjima

Razmatranje Roperove rezonancije

Different approaches to the Roper resonance are reviewed, revealing the multiple facet of this state and the need for some crucial experiments.Dajemo pregled nekoliko mogućih tumačenja Roperove rezonancije, te ukazujemo na složenost tog stanja, kao i na potrebu za novim mjerenjima

A chiral quark model for meson electro-production in the S11 partial wave

We calculate the meson scattering and electro-production amplitudes in the S11 partial wave in a coupled-channel approach that incorporates quasi-bound quark-model states. Using the quark wave functions and the quark-meson interaction from the Cloudy Bag Model, we obtain a good overall agreement with the available experimental results for the partial widths of the N(1535) and the N(1650) resonances as well as for the pion, eta and kaon electro-production amplitudes. Our model is consistent with the N(1535) resonance being dominantly a genuine three-quark state rather than a quasi-bound state of mesons and baryons.Comment: 10 pages, 13 figure

Solitons in a chiral quark model with non-local interactions

Hedgehog solitons are found in a chiral quark model with non-local interactions. The solitons are stable without the chiral-circle constraint for the meson fields, as was assumed in previous Nambu-Jona--Lasinio model with local interactions.Comment: 8 page