Polarization of $\tau$ leptons produced in ultra-high energy   neutrino-nucleon scattering
  We study the polarization vector of $\tau^-$ ($\tau^+$) leptons created in $\nu_\tau$ ($\bar{\nu}_\tau$) - 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. 
K\'evin Payet