We present a method for calculating center-of-mass corrections to hadron properties in soliton models and we apply the method to the soliton bag model. A coherent state is used to provide a quantum wave function corresponding to the mean-field approximation. This state is projected onto a zero-momentum eigenstate. States of nonzero momentum can be constructed from this with a Lorentz boost operator. Hence center-of-mass corrections can be made in a properly relativistic way. The energy of the projected zero-momentum state is the hadron mass with spurious center-ofmass energy removed. We apply a variational principle to our projected state and use three "virial theorems" to test our approximate solution. We also study projection of general one-mode states. Projection reduces the nucleon energy by up to 25%. Variation after projection gives a further reduction of less than 20%. Somewhat larger reductions in the energy are found for meson states.

In a previous paper we presented a method for calculating center-of-mass corrections to hadron properties in soliton models. Here we apply this method to the soliton bag model. We construct quantum bag solutions of quarks interacting with a scalar o field and color gauge fields in the onegluon-exchange approximation. The o part of Hilbert space is described by a coherent or general one-mode state. The Lorentz invariance of the theory requires the construction of momentum eigenstates with energies obeying the Einstein relation. Variation after projection onto zero momentum gives approximate mass eigenstates which are boosted relativistically onto states of nonzero momentum. This avoids the well-known Peierls-Yoccoz problem. Electromagnetic moments are evaluated. We obtain expressions for charge rms radii and nucleon magnetic moments, including recoil corrections. Other observables, which require the use of zero-momentum states are nucleon and meson masses, the axial-vector coupling constant g, (0) , and the pion decay constant f,. We determine the soliton bag parameters by a least-squares fit to the observed nucleon and pion masses, the charge rms radius and the magnetic moment of the proton and g~; the other observables are then "predicted."