Massless scalar and antisymmetric tensor fields in de Sitter space

The theory of a massless, minimally coupled scalar field φ is closely related to that of a massless, antisymmetric tensor field $A_{\mu \nu }$. It is shown that in de Sitter space the field $A_{\mu \nu }$ has a de Sitter-invariant state with a well-defined two-point function, while it is known that no such states exist for the scalar field φ.