Testing Dvali-Gabadadze-Porrati Gravity with Planck
  Recently, the Planck collaboration has released the first cosmological papers
providing the highest resolution, full sky, maps of the cosmic microwave
background (CMB) temperature anisotropies. In this paper we study a
phenomenological model which interpolates between the pure $\Lambda$CDM model
and the Dvali-Gabadadze-Porrati (DGP) braneworld model with an additional
parameter $\alpha$. Firstly, we calculate the "distance information" of Planck
data which includes the "shift parameter" $R$, the "acoustic scale" $l_A$, and
the photon decoupling epoch $z_\ast$ in different cosmological models and find
that this information is almost independent on the input models we use. Then,
we compare the constraints on the free parameter $\alpha$ of the DGP model from
the "distance information" of Planck and WMAP data and find that the Planck
data with high precision do not improve the constraint on $\alpha$, but give
the higher median value and the better limit on the current matter density
fraction $\Omega_m$. Then, combining the "distance information" of Planck
measurement, baryon acoustic oscillations (BAO), type Ia supernovae (SNIa) and
the prior on the current Hubble constant (HST), we obtain the tight constraint
on the parameter $\alpha < 0.20$ at $95\%$ confidence level, which implies that
the flat DGP model has been ruled out by the current cosmological data.
Finally, we allow the additional parameter $\alpha < 0$ in our calculations and
interestingly obtain $\alpha=-0.29\pm0.20$ ($68\%$ C.L.), which means the
current data slightly favor the effective equation of state $w_{\rm eff}<-1$.
More importantly, the tension between constraints on $H_0$ from different
observational data has been eased.
