THE PARTON DISTRIBUTIONS IN NUCLEONS - A QUARK-MODEL ANALYSIS

We use a laboratory frame description based on quark model wave functi ons to study the parton distributions in the nucleon. The present appr oach incorporates two major improvements, namely, it has the correct s upport and the renormalization group evolution is carried out to next- to-leading order. We obtain initially the parton distributions arising from the Isgur-Karl wave function. The failure of the latter to repro duce, even approximately, the data motivates us to analyze different s cenarios, i.e. additional high momentum components and nonvanishing gl uon distributions at the initial scale. We conclude that in order to u nderstand data at various scales complex models simultaneously, it is necessary to include high momentum components and/or valence gluons.