  By considering the irreducible representations of the Lorentz group, an
analysis of the different spin-2 waves is presented. In particular, the
question of the helicity is discussed. It is concluded that, although from the
point of view of representation theory there are no compelling reasons to
choose between spin-2 waves with helicity = + - 1 or helicity = + - 2,
consistency arguments of the ensuing field theories favor waves with helicity =
+ - 1.
