Peking Univ, Dept Phys, Beijing 100871, Peoples R China
; CCAST, World Lab, Beijing 100080, Peoples R China
; Acad Sinica, Inst High Energy Phys, Beijing 100039, Peoples R China
; Univ Tecn Federico Santa Maria, Dept Fis, Valparaiso, Chile
; CNRS, Ctr Phys Theor, F-13288 Marseille 9, France
; Nanjing Normal Univ, Dept Phys, Nanjing, Peoples R China
The flavor and helicity distributions of the Lambda and <(Lambda)over bar> hyperons for both valence and sea quarks are calculated in a perturbative QCD (pQCD) based model. We relate these quark distributions to the fragmentation functions of Lambda and <(Lambda)over bar>, and calculate the z-dependence of the longitudinal spin transfer to Lambda and <(Lambda)over bar> in lepton deep-inelastic scattering (DIS). It is shown that the spin transfer to the Lambda is compatible with the first HERMES results at DESY, and further tests are suggested. We also make predictions for the z-dependence of the Lambda and <(Lambda)over bar> longitudinal polarizations in neutrino (antineutrino) DIS processes. We investigate the sea contribution to the fragmentation functions, and we testa possible scenario where the sea quarks in Lambda (or the sea antiquarks in <(Lambda)over bar>) are negatively polarized, whereas the sea antiquarks in the Lambda (or the sea quarks in <(Lambda)over bar>) are positively polarized. The asymmetry of the polarized fragmentation functions of the sea quarks and antiquarks to Lambda and <(Lambda)over bar> provides a way to understand the different behavior between the Lambda and <(Lambda)over bar> spin transfers observed in the recent E665 experiment at FNAL.