Roper Electroproduction Amplitudes in a Chiral Confinement Model

A description of the Roper using the chiral chromodielectric model is presented and the transverse $A_{1/2}$ and the scalar $S_{1/2}$ helicity amplitudes for the electromagnetic Nucleon--Roper transition are obtained for small and moderate $Q^2$. The sign of the amplitudes is correct but the model predictions underestimate the data at the photon point. Our results do not indicate a change of sign in any amplitudes up to $Q^2\sim1$ GeV$^2$. The contribution of the scalar meson excitations to the Roper electroproduction is taken into account but it turns out to be small in comparison with the quark contribution. However, it is argued that mesonic excitations may play a more prominent role in higher excited states.Comment: 10 pages, 8 figures, uses World Scientific macros. Talk presented at EMI2001 in Osaka, Japa

N^* electroproduction amplitudes in a model with dynamical confinement

The Roper resonance is described in a chiral version of the chromodielectric model as a cluster of three quarks in radial-orbital configuration (1s)$^2$(2s)$^1$, surrounded by $\pi$ and $\sigma$-meson clouds and by a chromodielectric field which assures quark dynamical confinement. Radial profiles for all fields are determined self-consistently for each baryon. Transverse $A_{1/2}$ and scalar $S_{1/2}$ helicity amplitudes for the nucleon-Roper transition are calculated. The contribution of glueball and $\sigma$-meson vibrations is estimated; although small for N(1440), the $\sigma$ contribution can be large for N(1710).Comment: 12 pages, 6 figures, uses elsevier macro

Uloga pionskog oblaka u nukleonskim faktorima oblika

In the linear sigma model and in the chromodielectric model, it is shown how the pion cloud enhances the electric polarizability, the electroexcitation of the ∆ and the axial form factor, and how it reduces the magnetic polarizability.U linearnom sigma modelu i u kromodielektričnom modelu se pokazuje kako pionski oblak povećava električnu polarizivnost, elektrouzbudu ∆ i aksijalni faktor oblika, te kako smanjuje magnetsku polarizivnost

Axial amplitudes for Delta excitation in chiral quark models

We study the axial amplitudes for the N-Delta transition in models with quarks and chiral mesons. A set of constraints on the pion field is imposed which enforces PCAC and the off-diagonal Goldberger-Treiman relation. The quark contribution to the amplitudes in general strongly underestimates the C^A_5 amplitude as well as the piNDelta strong coupling constant. We show that the results are considerably improved in models that, in addition to the pion cloud, incorporate a fluctuating sigma field inside the baryon.Comment: 13 pages LaTeX2e, 4 EPS figures within the text; Requires elsart.cls (Submitted for publication in Phys. Lett. B). Section 4 revise