Crosstalk between DGP branes
  If two DGP branes carry U(1) gauge theories and overlap, particles of one
brane can interact with the photons from the other brane. This coupling
modifies in particular the Coulomb potentials between charges from the same
brane in the overlapping regions. The coupling also introduces Coulomb
interactions between charges from the different branes which can generate
exotic bound states.
  The effective modification of the fine structure constant in the overlap
region generates a trough in signals at the redshift of the overlap region and
an increase at smaller or larger redshift, depending on the value of the
crosstalk parameter. This implies potentially observable perturbations in the
Lyman-alpha forest if our 3-brane overlapped with another 3-brane in a region
with redshift z<6. Crosstalk can also affect structure formation by enhancing
or suppressing radiative cooling.
