Shadowing Aspects of Nuclear Parton Distributions
  Various shadowing aspects of nuclear parton distributions are discussed in a parton-model framework. We explain existing $x$ dependent data of $F_2^A/F_2^D$, then the model is applied to a flavor asymmetry $\bar u-\bar d$ in a nucleus, to shadowing in valence-quark distributions, and to nuclear dependence of $Q^2$ evolution. First, we find that a finite nuclear $\bar u-\bar d$ distribution could be possible due to nuclear interactions even in the flavor symmetric case in the nucleon ($\bar u -\bar d$=0). Second, it is indicated that valence-quark shadowing could be used for discriminating among various shadowing models. Third, we find that nuclear dependence of $Q^2$ evolution $\partial [F_2^{Sn}/F_2^C]/ \partial [\ln Q^2]$, which was found by NMC, is essentially understood by modification of parton distributions in nuclei. However, higher-twist effects in nuclear interactions could be tested by studying the details of the nuclear $Q^2$ evolution. 
S. Kumano (Saga Univ.)