Hello! I am a bit confused about neutrinos in the standard model. The vertex of the weak interaction charged current, implies that any neutrino interacting through the charged current must be left handed. However the neutral current allows coupling to the right handed particles, too (and we see that in the interactions with charged leptons). Why is it not possible for a Z boson to decay to a pair for neutrino-antineutrino, in which the neutrino is right handed? I.e. why don't we have any right handed neutrinos in the standard model? Thank you!