Flavor and Spin Structure of $\Lambda$-Baryon at Large x

It is shown that a perturbative QCD (pQCD) based analysis and the SU(6) quark-diquark model give significant different predictions concerning the flavor and spin structure for the quark distributions of the $\Lambda$-baryon near $x=1$. Detailed predictions for the ratios $u(x)/s(x)$ of unpolarized quark distributions, $\Delta s(x)/s(x)$ of valence strange quark, and $\Delta u(x)/u(x)$ of valence up and down quarks of the $\Lambda$ are given from the quark-diquark model and from a pQCD based model. It is found that the up and down quarks are positively polarized at large $x$, even though their net spin contributions to the $\Lambda$ might be zero or negative. The significant difference for $u(x)/s(x)$ between the two different approaches are predicted. The prediction of positively polarized up and down quarks inside the $\Lambda$ at large $x$ has been supported by the available data of $\Lambda$-polarization in $Z$ decays and also by the most recent HERMES result of spin transfer to the $\Lambda$ in deep elastic scattering of polarized lepton on the nucleon target.