相关论文: Empirical parametrizations of the resonance amplit…
Some empirical parametrizations of the $\gamma^\ast N \to N(1535)$ transition amplitudes violates the Siegert's theorem, that relates the longitudinal and the transverse amplitudes, in the pseudo-threshold limit (nucleon and resonance at…
In the nucleon electroexcitation reactions, $\gamma^\ast N \to R$, where $R$ is a nucleon resonance ($N^\ast$), the electric amplitude $E$, and the longitudinal amplitude $S_{1/2}$, are related by $E \propto \frac{\omega}{|{\bf…
The large $N_c$ limit provides relations that can be used to calculate the $\gamma^\ast N \to \Delta(1232)$ quadrupole form factors at low and intermediate $Q^2$ under the assumption of the pion cloud dominance. There are two limitations in…
The novel measurements of the $\gamma^\ast N \to \Delta(1232)$ Coulomb quadrupole form factor in the range $Q^2=0.04$--0.13 GeV$^2$ changed the trend of the previous data. With the new data the electric and Coulomb form factors are both in…
Models based on $SU(6)$ symmetry breaking and large $N_c$ limit provide relations between the pion cloud contributions to the $\gamma^\ast N \to \Delta(1232)$ quadrupole form factors, electric ($G_E$) and Coulomb ($G_C$), and the neutron…
We utilize non-perturbative and fully relativistic methods to calculate the\thinspace \thinspace $\Delta N\gamma $ electromagnetic transition amplitudes $G_{M}^{*}(q^{2})$ (related to the magnetic dipole moment $% M_{1^{+}}^{3/2}(q^{2})$),…
The study of the $\gamma^* N\rightarrow \Delta$ reaction presents the best quantitative method to explore the deviation of hadron shapes from spherical symmetry (nonspherical amplitudes). Significant non-spherical electric (E2) and Coulomb…
We discuss how electromagnetic properties provide useful tests of the nature of resonances, and we study these properties for the N*(1535) which appears dynamically generated from the strong interaction of mesons and baryons. Within this…
The representation of the wave functions of the nucleon resonances within a relativistic framework is a complex task. In a nonrelativistic framework the orthogonality between states can be imposed naturally. In a relativistic…
We review some basic properties of the N-Delta transition axial amplitudes and relate them to the strong pi-N-Delta form-factor. In models with the pion cloud we derive a set of constraints on the pion wave function which guaranty the…
We compute the amplitudes for the electromagnetic $\gamma_v N \to \Delta$ transition in the framework of soliton models with quarks and mesons. The ratios E2/M1 and C2/M1 as functions of the photon four-momentum squared are dominated by the…
We obtain the electromagnetic form factors of the $\gamma N\Delta$ transition by analyzing recent pion-electroproduction data using a fully relativistic dynamical model. Special care is taken to satisfy Ward-Takahashi identities for the…
The helicity amplitudes of the $N(1520)$ and $N(1535)$ resonances in the $\gamma^*p\to N^*$ electromagnetic transition are studied in the constituent quark model using the impulse approximation, with the proton and resonances assumed to be…
We discuss the results of the covariant spectator quark model for the several $\gamma^\ast N \to N^\ast$ transitions, where $N$ is the nucleon and $N^\ast$ a nucleon excitation. More specifically, we present predictions for the form factors…
We present some predictions for the $\gamma^\ast N \to N^\ast$ transition amplitudes, where $N$ is the nucleon, and $N^\ast$ is a nucleon excitation from the third resonance region. First we estimate the transition amplitudes associated…
Electroproduction form factors describing the $\gamma^\ast p \to \Delta^+(1232), \Delta^+(1600)$ transitions are computed using a fully-dynamical diquark-quark approximation to the Poincar\'e-covariant three-body bound-state problem in…
The resonant electric quadrupole amplitude in the transition $\gamma N\leftrightarrow\Delta(1232)$ is of great interest for the understanding of baryon structure. Various dynamical models have been developed to extract it from the…
To study cross sections and polarization asymmetries for the processes $e p \to e n \pi^+$ and $e p \to e p \pi^0$ in the backward region, we develop a flexible phenomenological model for nucleon-to-pion transition distribution amplitudes…
The data associated with the electromagnetic excitations of the nucleon ($\gamma^\ast N \to N^\ast$) are usually parametrized by helicity amplitudes at the resonance $N^\ast$ rest frame. The properties of the $\gamma^\ast N \to N^\ast$…
The form factors, as well as the helicity amplitudes for the $\gamma^\ast N \to N(1535)$ transition are calculated in framework of the QCD light cone sum rules. The contamination coming from diagonal transition is eliminated by considering…