Symmetries and similarities for spin orientation parameters in e+e−→ZH,Zγ,ZZ at SM thresholds

We consider the spin orientation 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,Zγ) or are very similar (e+e−→ZZ). In addition, we present interesting symmetry properties for the spin orientation parameters.