Strong decays of N∗(1535)N^{*}(1535) in an extended chiral quark model

The strong decays of the $N^{*}(1535)$ resonance are investigated in an extended chiral quark model by including the low-lying $qqqq\bar{q}$ components in addition to the $qqq$ component. The results show that these five-quark components in $N^{*}(1535)$ contribute significantly to the $N^{*}(1535)\to N\pi$ and $N^{*}(1535)\to N\eta$ decays. The contributions to the $N\eta$ decay come from both the lowest energy and the next-to-lowest energy five-quarks components, while the contributions to the $N\pi$ decay come from only the latter one. Taking these contributions into account, the description for the strong decays of $N^{*}(1535)$ is improved, especially, for the puzzling large ratio of the decays to $N\eta$ and $N\pi$.Comment: 6 pages, 1 figur

Model-independent resonance parameter extraction using the trace of K and T matrices

A model-independent method for the determination of Breit-Wigner resonance parameters is presented. The method is based on eliminating the dependence on the choice of channel basis by analyzing the trace of the K and T matrices in the coupled-channel formalism, rather than individual matrix elements of the multichannel scattering matrix.Comment: 6 pages, 16 figure

η\eta production off the proton in a Regge-plus-chiral quark approach

A chiral constituent quark model approach, embodying s- and u-channel exchanges,complemented with a Reggeized treatment for t-channel is presented. A model is obtained allowing data for $\pi^- p \to \eta n$ and $\gamma p \to \eta p$ to be describe satisfactorily. For the latter reaction, recently released data by CLAS and CBELSA/TAPS Collaborations in the system total energy range $1.6 \lesssim W \lesssim 2.8$ GeV are well reproduced due to the inclusion of Reggeized trajectories instead of simple $\rho$ and $\omega$ poles. Contribution from "missing" resonances is found to be negligible in the considered processes.Comment: 23 pages.4 figures,4 tables, to appear in Phys.Rev.

A (p/E) Calculation of Strong Pionic Decays of Baryons

Strong pionic decays of baryons are studied in a non-relativistic quark model framework via a convergent (p/E) expansion of the transition operator. Results are compared to the ones obtained within a more conventional (p/m) expansion.Comment: 16 pages, LaTeX, using amssymb.st

Baryon Current Matrix Elements in a Light-Front Framework

Current matrix elements and observables for electro- and photo-excitation of baryons from the nucleon are studied in a light-front framework. Relativistic effects are estimated by comparison to a nonrelativistic model, where we use simple basis states to represent the baryon wavefunctions. Sizeable relativistic effects are found for certain transitions, for example, to radial excitations such as that conventionally used to describe to the Roper resonance. A systematic study shows that the violation of rotational covariance of the baryon transition matrix elements stemming from the use of one-body currents is generally small.Comment: 32 pages, LaTeX, 10 postscript figures, uses epsf.sty; figures uuencoded with uufiles (or available by request in .ps or hardcopy form

The role of the pion cloud in electroproduction of the Δ\Delta(1232)

We calculate the ratios $E2/M1$ and $C2/M1$ of the multipole amplitudes for electroproduction of the $\Delta$(1232) in the range of photon virtuality $0<-K^2<1$~GeV$^2$ in a chiral chromodielectric model and a linear $\sigma$-model. We find that relatively large experimental values can be explained in terms of the pion contribution alone; the contribution arising from d-state quark admixture remains below 10\%. We describe the pion cloud as a coherent state and use spin and isospin projection to obtain the physical nucleon and the $\Delta$. The $A_{1/2}$ and $A_{3/2}$ amplitudes are reasonably well reproduced in the $\sigma$-model; in the chromodielectric model, however, they are a factor of two too small.Comment: 10 pages LaTeX2e, 3 LaTeX figures within the text; Requires elsart.cls (included in the self-unpacking uuencoded gzipped file). (Accepted for publication in Phys. Lett. B

Electromagnetic Form Factors of the Nucleon in a Relativistic Quark Pair Creation Model

We study the effects of the | qqq q\bar{q} > component of the hadronic wave function on the description of the electromagnetic structure of the nucleon. Starting with a qqq baryonic wave function which describes the baryonic and mesonic low energy spectrum, the extra q\bar{q} pair is generated through a relativistic version of the 3P_0 model. It is shown that this model leads to a renormalization of the quark mass that allows one to construct a conserved electromagnetic current. We conclude that these dynamical relativistic corrections play an important role in reproducing the Q2 dependence of the electromagnetic form factors at low Q^2.Comment: 15 pages, 3 figures. Minor change