Boosting the bag

The Lorentz boost transformation for the soliton bag model is constructed in the mean-field approximation. Assuming that the standard static-bag wave function is equivalent to the zero-momentum eigenstate, the Lorentz boost transformation generates quark wave functions corresponding to a moving bag. We demonstrate that the mean-field energy and momentum of such a moving bag are related to the energy of the bag at rest by the correct Lorentz-transformation formulas. The boosted quark wave functions are used to investigate relativistic recoil corrections to hadronic form factors. Electromagnetic and axial-vector form factors are discussed, as well as the pion-nucleon vertex corresponding to a hybrid chiral bag model. Various types of bags (e.g., MIT type and SLAC type) are considered. It is shown that ignoring quark binding in the boost transformation leads to an overestimate of recoil corrections to magnetic moments. Relativistic recoil generally hardens the form factors. The proton charge radius is decreased by about 15% compared to the static-approximation values. The magnetic moment is changed by less than 10%. The inclusion of recoil corrections leads to reasonable agreement with experiment for all form factors considered if the bag radius (for an MIT bag) is about 1.3 fm. A comparison is made with other works on this topic.