Why should a graviton (if it exists) decay into 2 Z bosons?
My understanding is that the graviton is supposed to be a massless spin-2 boson and that it is the conservation laws for energy and spin and the rest of quantum numbers that allow a decay.
Now I see that the above prediction makes sense, since the z boson is spin-1 and it is its own antiparticle, thus, all of its flavour quantum numbers and charges are zero. But what I find a bit more problematic or involved is that the Z boson is massive (almost 80 times as massive as the proton). For example in the case of the observation of ttH production, they say that the Higgs can not decay into top quarks because they're too heavy... Can someone shed some light here?