Key points are not available for this paper at this time.
It is shown by an explicit calculation that the excitations about the self-accelerating cosmological solution of the Dvali-Gabadaze-Porrati model contain a ghost mode. This raises serious doubts about viability of this solution. Our analysis reveals the similarity between the quadratic theory for the perturbations around the self-accelerating universe and an Abelian gauge model with two St\"uckelberg fields.
Gorbunov et al. (Tue,) studied this question.