Symmetries and similarities for spin orientation parameters in e^+ e^- -> ZH, Zγ, ZZ at SM thresholds

We consider the spin orentation of the final Z bosons for the processes in the Standard Model. We demonstrate that at the threshold energies of these processes the analytical expressions for the Z boson polarization vectors and alignment tensors coincide (e^+ e^- -> ZH, Z\gamma) or are very similar (e^+ e^- -> ZZ). In addition, we present interesting symmetry properties for the spin orientation parameters.