Abstract The model of Dvali, Gabadadze, and Porrati (DGP) gives a simple geometrical
setup in which gravity becomes 5-dimensional at distances larger than a length scale λ
DGP. We show that this theory has strong interactions at a length scale λ 3∼(λ DGP 2/MP)
1/3. If λ DGP is of order the Hubble length, then the theory loses predictivity at distances
shorter than λ 3∼ 1000 km. The strong interaction can be viewed as arising from a
longitudinaleaten Goldstone'mode that gets a small kinetic term only from mixing with …

The model of Dvali, Gabadadze, and Porrati (DGP) gives a simple geometrical setup in
which gravity becomes 5-dimensional at distances larger than a length scale λ< sub> DGP.
We show that this theory has strong interactions at a length scale λ< sub> 3∼(λ< sub>
DGP< sup> 2/M< sub> P)< sup> 1/3. If λ< sub> DGP is of order the Hubble length, then the
theory loses predictivity at distances shorter than λ< sub> 3∼ 1000 km. The strong
interaction can be viewed as arising from a longitudinaleaten Goldstone'mode that gets a …