Spectrum from the warped compactifications with the de Sitter universe
Minamitsuji, Masato (Kyoto University)

We discuss the spectrum of the tensor metric perturbations and the stability of warped compactifications with the de Sitter spacetime in the higher-dimensional gravity with and without matter fields. The spacetime structure is given in terms of the warped product of the noncompact direction, the spherical internal dimensions and the four-dimensional de Sitter spacetime. To realize the finite bulk volume, we construct the brane world model by the cut-copy-paste method. We compactify the spherical directions on the brane. In any case, we ensure the existence of the massless zero mode and the mass gap with the Kaluza-Klein (KK) continuum due to the warp. Although the brane involves the spherical dimensions, no light mode is excited. We also investigate the scalar perturbations, and show that the model is unstable due to the tachyonic bound state which seems to have the universal negative mass square, irrespective of the number of spacetime dimensions and kinds of the bulk matter. We also discuss the four-dimensional effective theory and the moduli stabilization.