Cosmological Constraints on DGP Braneworld Gravity with Brane Tension

TL;DR

This study uses cosmological data to test DGP braneworld gravity models, finding that a cosmological constant or brane tension is necessary, and that modifications to gravity are strongly constrained.

Contribution

It provides the first comprehensive MCMC analysis of both DGP branches using combined CMB, galaxy, and supernova data, constraining the crossover scale and the need for brane tension.

Findings

Brane tension or a cosmological constant is required at high significance.

The crossover scale must be greater than 3-3.5 times the Hubble scale.

Galaxy cross-correlation data significantly constrains the normal branch.

Abstract

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.