ar X iv : h ep - p h / 94 07 31 5 v 1 1 8 Ju l 1 99 4 Convolution model for the structure functions of the nucleon

We start from an MIT-bag model calculation which provides information about the constituent quark distributions in the nucleon. The constituent quarks, however, are themselves considered as complex objects whose par-tonic substructure is resolved in deep inelastic scattering. This gives rise to structure functions of the constituent quarks which, in the unpolarized case, are fitted to data at a fixed scale employing three model parameters. Using Q 2 –evolution equations the data are also well described at other scales. For the spindependent structure functions g p,n 1 we additionally have to introduce polarization functions for valence and sea quarks which are determined by exploiting the x–dependence of the available proton data only. A negatively polarized sea in the range x ≥ 0.01 is suggested. We are then capable of predicting the shape of the neutron structure function g n 1 which turns out to be in good agreement with experiment. Finally we present an estimate for the transversely polarized structure function g 2 , offering the possibility of extracting the twist–3 contribution and rating its importance.