Search for indirect new physics effects in e+e− → W+W− at linear colliders with polarized beams

We discuss the potential of a 0.5 TeV linear collider to explore manifestations of extended (or alternative) electroweak models of current interest, through measurements of the reaction e+e− → 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′ mixing, showing in particular the usefulness of polarization in order to disentangle these effects.