Observational constraints on self-accelerating cosmology

The Dvali-Gabadadze-Porrati (DGP) braneworld model provides a simple alternative to the standard lambda cold dark matter cosmology, with the same number of parameters. There is no dark energy—the late universe self-accelerates due to an infrared modification of gravity. We compute the joint constraints on the DGP model from supernovae, the cosmic microwave background shift parameter, and the baryon oscillation peak in the Sloan Digital Sky Survey luminous red galaxy sample. Flat DGP models are within the joint 2 sigma contour, but the lambda cold dark matter model provides a significantly better fit to the data. These tests are based on the background dynamics of the DGP model, and we comment on further tests that involve structure formation.

Figure 1

The parameter space for DGP models. The dotted (red) curve is the flat case, with closed models above and open models below; the dot-dashed (black) curve demarcates models that are currently accelerating (above) from those decelerating (below); the shaded (blue) region contains expanding models that bounce in the past, i.e. do not have a big bang; the likelihood contours are fits to the SNe Gold data [dashed (brown)] and Legacy data [solid (blue)].

Figure 2

Likelihood contours for the CMB shift parameter $S$ in DGP (left) and LCDM (right).

Figure 3

Joint constraints [solid thick (blue)] on DGP models from the SNe data [solid thin (yellow)], the BO measure $A$ [dotted (green)] and the CMB shift parameter $S$ [dot-dashed (red)]. The left plot uses SNe Gold data, the right plot uses SNLS data. The thick dashed (black) line represents the flat models, ${\Omega }_K=0$.

Figure 4

As in Fig. 3, but for LCDM.