Around a flat background, a plane wave propagating in the $z$ direction is given by $h_{\mu\nu} = \epsilon_{\mu\nu} \cos(\omega t -kz)$.
What is the generalisation of this to a de Sitter background?
Around a flat background, a plane wave propagating in the $z$ direction is given by $h_{\mu\nu} = \epsilon_{\mu\nu} \cos(\omega t -kz)$.
What is the generalisation of this to a de Sitter background?
To lowest order in $\Lambda$, i.e. taking the metric to be Minkowski plus a perturbation from $\Lambda$, plus a perturbation from the plane wave, the plane wave is given in the following papers
The fate of a gravitational wave in de Sitter spacetime About the propagation of the Gravitational Waves in an asymptotically de-Sitter space