Search for new physics indirect effects in $e^{+}{e}^{-}\to W^{+}{W}^{-}$ at linear colliders with polarized beams

We discuss the potential of a $0.5TeV$ linear collider to explore manifestations of extended (or alternative) electroweak models of current interest, through measurements of the reaction $e^{+}{e}^{-}\to W^{+}{W}^{-}$ with both initial and final states polarization. Specifically, we consider the possibility to put stringent constraints on lepton mixing (or extended lepton couplings) and $Z-Z^{\mathrm{\prime }}$ mixing, showing in particular the usefulness of polarization in order to disentangle these effects.