相关论文: Electromagnetic multipoles - theory issues
The results for the elastic nucleon form factors and the electromagnetic transition amplitudes to the Delta(1232) resonance, obtained with the Hypercentral Constituent Quark Model with the inclusion of a meson cloud correction are briefly…
The predictions of the hypercentral Consituent Quark Model for the nucleon helicity amplitudes are briefly reported. Some future perspectives are also discussed.
The unitary isobar model MAID has been extended and used for a partial wave analysis of pion photo- and electroproduction in the resonance region W < 2 GeV. Older data from the world data base and more recent experimental results from…
The hypercentral CQM, which is inspired by Lattice QCD calculations for quark-antiquark potentials, is presented, stressing its underlying symmetry. Its results for the spectrum, the helicity amplitudes and the elastic form factors are…
We report on the recent results of the hypercentral constituent quark model. The model contains a spin independent three-quark interaction which is inspired by QCD lattice calculations and reproduces the average energy values of the SU(6)…
The hypercentral constituent quark model contains a spin independent three-quark interaction inspired by lattice QCD calculations which reproduces the average energy of SU(6) multiplets. The splittings are obtained with a residual…
A recent analysis of pion photo-production multipoles using p(g,pi0) data from Mainz is repeated, successively adding constraints from other observables and varying the number of fitted partial waves. The original analysis is shown to have…
The present contribution continues and extends foregoing work on the calculation of electroweak form factors of hadrons using the point-form of relativistic quantum mechanics. Here we are particularly interested in studying pionic effects…
We report on the recent results of the hypercentral Constituent Quark Model (hCQM). The model contains a spin independent three-quark interaction which is inspired by Lattice QCD calculations and reproduces the average energy values of the…
We show that recent experiment data for the ratios $E_{1^+}/M_{1^+}$ and $S_{1^+}/M_{1^+}$ can be explained in a dynamical model for electromagnetic production of pions, together with a simple scaling assumption for the bare $\gamma^* N…
Strange quark contributions to the proton magnetic moment are estimated from a consideration of baryon magnetic moment sum rules. The environment sensitivity of quark contributions to baryon moments is emphasized. Pion cloud contributions…
We report on ongoing work to determine the pion-cloud contribution to the electromagnetic $N\rightarrow\Delta$ transition form factors. The starting point is an $SU(6)$ spin-flavor symmetric constituent-quark model with instantaneous…
This talk presents issues pertaining to the quark structure of the pion within QCD, both from the theoretical and from the experimental point of view. We review and discuss the pion-photon transition form factor and the pion's…
Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the $Q^2$…
We study how the electromagnetic structure of the nucleon is influenced by a pion cloud. To this aim we make use of a constituent-quark model with instantaneous confinement and a pion that couples directly to the quarks. To derive the…
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…
Pion electroproduction amplitudes predicted by three theoretical models in the $Q^2 \leq 0.5$ (GeV/c)$^2$ region are compared. The objective is to facilitate the analyses of the data from new experiments on investigating the pion cloud…
The electric polarizability of mesons, in particular, that of the charged pion, is studied in the framework of a semirelativistic description of hadrons as bound states of valence quarks in terms of a Hamiltonian composed of the…
The nucleon polarizabilities alpha(E) and beta(M) are studied in the context of the perturbative chiral quark model. We demonstrate that meson cloud effects are sufficient to explain the electric polarizability of nucleon. Contributions of…
Using the helicity formalism, we compute the contribution of a quark-antiquark pair to the tree-level multigluon amplitudes in the high-energy limit. The $\bar{q}\, q$-pair production is absent in the leading-log formalism, but contributes…