Modification of parton distributions in nuclei

Nuclear parton distributions are studied in a parton model with rescaling and recombination mechanisms. Parton x distributions are first calculated at Q^2=1 GeV^2 by the model, and they are evolved to larger Q^2 in order to be compared with various F_2 data. The experimental shadowing is explained by the parton-recombination effects. Then, the modification of sea-quark and gluon distributions is investigated. We show x and Q^2 dependent results of the ratios S_A/S_D and G_A/G_D. They indicate significant shadowing at small x and large ratios in the medium-x region. Our theoretical results should be tested by future experiments, for example, at RHIC (Relativistic Heavy Ion Collider). Furthermore, our studies are important for finding a signature of the quark-gluon plasma in heavy-ion reactions. We also indicate that nuclear effects in the deuteron should be taken into account for finding the accurate F_2 structure function of the neutron.