We study the polarization vector of τ− (τ+) leptons created in
ντ (νˉτ) - Nucleon deep inelastic scattering. Our work is
oriented toward ultra-high energy particles relevant for cosmic-rays
experiments. The goal of this paper is to derive relevant informations to
constrain the systematic uncertainties that follow from the lack of knowledge
about this point particularly when studying Earth-skimming neutrinos