  We study the proposal that a de Sitter (dS) universe with an Anti-de Sitter
(AdS) bubble can be replaced by a dS universe with a boundary CFT. To explore
this duality, we consider incident gravitons coming from the dS universe
through the bubble wall into the AdS bubble in the original picture. In the
dual picture, this process has to be identified with the absorption of
gravitons by CFT matter. We have obtained a general formula for the absorption
probability in general $d+1$ spacetime dimensions. The result shows the
different behavior depending on whether spacetime dimensions are even or odd.
We find that the absorption process of gravitons from the dS universe by CFT
matter is controlled by localized gravitons (massive bound state modes in the
Kaluza-Klein decomposition) in the dS universe. The absorption probability is
determined by the effective degrees of freedom of the CFT matter and the
effective gravitational coupling constant which encodes information of
localized gravitons. We speculate that the dual of $d+1$ dimensional dS
universe with an AdS bubble is also dual to a $d$ dimensional dS universe with
CFT matter.
