Flavor asymmetry of polarized and unpolarized sea quark distributions in the large-N_c limit

We summarize recent attempts to calculate the flavor asymmetry of the nucleon's sea quark distributions in the large-$N_c$ limit, where the nucleon can be described as a soliton of an effective chiral theory. We discuss the leading-twist longitudinally polarized and transversity antiquark distributions, $\Delta\bar u (x) - \Delta\bar d (x)$ and $\delta\bar u (x) - \delta\bar d (x)$, as well as the unpolarized one, $\bar u (x) - \bar d (x)$, which appears only in the next-to-leading order of the $1/N_c$-expansion. Results for $\bar u (x) - \bar d (x)$ are in good agreement with the recent Drell-Yan data from the FNAL E866 experiment. The longitudinally polarized antiquark asymmetry, $\Delta\bar u (x) - \Delta\bar d (x)$, is found to be larger than the unpolarized one.