Electroexcitation of the Roper resonance in the relativistic quark models

The amplitudes of the transition γ∗N → P11(1440) are calculated within light-front relativistic quark model assuming that the P11(1440) is the first radial excitation of the 3q nucleon state. The results are compared with those obtained in close approaches by other authors and with standard nonrelativistic calculations. One of the reasons for this study was to present all these results within unified definition of helicity amplitudes consistent with the definition used in the extraction of the helicity amplitudes from experimental data in one-pion electroproduction. The results of relativistic quark models are qualitatively in good agreement with each other and differ strongly from nonrelativistic calculations. At small Q , these results for the transverse amplitude A1/2 are consistent, but fail to reproduce experimental data. The most probable explanation of this discrepancy is the absence of pion cloud contribution in the approaches under consideration.