Modification of the laws of gravity in the DGP model by the presence of
  a second DGP brane
  We investigate how the laws of gravity change in the DGP model, if we add a
second, parallel 3-brane, endowed with a localized gravitational curvature
term. We calculate the gravitational potential energy between two static point
sources localized on different branes. We discover a new length scale, which is
equal to the geometric mean of the DGP cross-over scale and the separation of
the two branes in the extra dimension. For distances, which are larger than
this new length scale, we recover the original DGP result, but for smaller
distances the gravitational potential is weaker. Furthermore, a region emerges,
where a 4-dimensional observer measures a distance independent force. We
discuss a possible application of the present scenario for deriving rotation
curves of low surface brightness galaxies. Using the Kaluza-Klein description,
we observe a curious pattern, in which even and odd KK-modes contribute to the
attractive and repulsive parts of the gravitational potential, respectively.
Finally, since this setup allows for the existence of a sector of particle
species that are interacting arbitrarily weakly with "our" sector, we discuss
the implications of this phenomenon for black holes and the bound on the number
of species. We find that the behavior is qualitatively different from theories
with a normalizable zero-mode graviton.
