Cosmological Constraints on DGP Braneworld Gravity with Brane Tension
  We perform a Markov Chain Monte Carlo analysis of the self-accelerating and
normal branch of Dvali-Gabadadze-Porrati braneworld gravity. By adopting a
parameterized post-Friedmann description of gravity, we utilize all of the
cosmic microwave background data, including the largest scales, and its
correlation with galaxies in addition to the geometrical constraints from
supernovae distances and the Hubble constant. We find that on both branches
brane tension or a cosmological constant is required at high significance with
no evidence for the unique Dvali-Gabadadze-Porrati modifications. The
cross-over scale must therefore be substantially greater than the Hubble scale
H_0 r_c > 3 and 3.5 at the 95% CL with and without uncertainties from spatial
curvature. With spatial curvature, the limit from the normal branch is
substantially assisted by the galaxy cross-correlation which highlights its
importance in constraining infrared modifications to gravity.
