Covariant two-point function for linear gravity in de Sitter space
  The Wightman two-point function for the gravitational field in the linear approximation (the rank-2 ``massless'' tensor field) on de Sitter space has a pathological behaviour for large separated points (infrared divergence). This behaviour can be eliminated in the two-point function for the traceless part of this field if one chooses the Gupta-Bleuler vacuum. But it is not possible to do the same for the pure trace part (conformal sector). We briefly discuss the consequences of this pure trace behaviour for inflationary models. 
M. V. Takook