Effects of core motion on the nucleon electric form factors.

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When the nucleon is described as the self-consistent nontopological soliton ground state of a translation-invariant model Hamiltonian for a nonstatic baglike core interacting with a pion field, the motion of the core is shown to have a significant effect on the proton and neutron electric form factors, as compared to previous cloudy-bag-model (CBM) calculations that neglect the core motion and treat the baglike core as a static source of pion field. In the translation-invariant model, the charge density of the nucleon has contributions from the core and from the pion cloud, as in the usual static CBM; in addition, and in contrast to the usual static CBM, there are effects due to the spreading of the core charge density as a result of the self-consistent motion of the core within the pion field that it generates. The spreading of the core density tends to weaken the core-pion interaction for a fixed bag radius so that the binding of the core-pion system is less than in the static cloudy bag. Hence, the motion of the core softens the electric form factors as compared to static CBM calculations.