On the Gravitational Wave in de Sitter Spacetime
  For there is always a wrong sign in the mass of graviton in the so-called perturbation expansion approximation of both Minkowski and de Sitter spacetimes, the existence of gravitational wave from the metric perturbation of de Sitter spacetime is doubtful. We try another way to start from the assumption that the gravitational wave equation should be both general covariant and conformal invariant and find that graviton is no longer a part of metric field, it has an effective mass of $m_g=\sqrt{R/6}=% \sqrt{2\Lambda/3}$ with correct sign in de Sitter spacetime, though it's intrinsic mass remains zero. 
Liao Liu