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, Z gamma) or are very similar (e(+)e(-) -> ZZ). In addition, we present interesting symmetry properties for the spin orientation parameters. (C) 2010 Elsevier B.V. All rights reserved.