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Deep-inelastic structure functions are calculated from a Peierls-Yoccoz-projected MIT bag wave function. The calculation yields quark distribution functions that have the correct support as a function of Bjorken x. These functions are evolved to Q 2 = 15 Gev2 using QCD perturbation theory, where they are shown to disagree with experiment. Possible improvements are discussed.

Using a quark model, we study the effect of charge symmetry breaking on the valence quark distributions of the nucleon. The effect due to quark mass differences and the Coulomb interaction of the electrically charged quarks is calculated and, in contrast to recent claims, found to be small. In addition, we investigate the effect of charge symmetry breaking in the confining interaction, and in the perturbative evolution equations used to relate the quark model distributions to experiment. We find that both these effects are small, and that the strong charge symmetry breaking effect included in the scalar confining interactions may be distinguishable from that generated by quark mass differences. 0

Recent calculations of charge symmetry violation ͑CSV͒ in the valence quark distributions of the nucleon have revealed that the dominant symmetry breaking contribution comes from the mass associated with the spectator quark system. Assuming that the change in the spectator mass can be treated perturbatively, we derive a model-independent expression for the shift in the parton distributions of the nucleon. This result is used to derive a relation between the charge-and flavor-asymmetric contributions to the valence quark distributions in the proton, and to calculate the CSV contribution to the nucleon sea. The CSV contribution to the Gottfried sum rule is also estimated, and found to be small. ͓S0556-2813͑98͒02208-0͔