Exploring the full parameter space for an interacting dark energy model
  with recent observations including redshift-space distortions: Application of
  the parametrized post-Friedmann approach
  Dark energy can modify the dynamics of dark matter if there exists a direct
interaction between them. Thus a measurement of the structure growth, e.g.,
redshift-space distortions (RSD), can provide a powerful tool to constrain the
interacting dark energy (IDE) models. For the widely studied $Q=3\beta
H\rho_{de}$ model, previous works showed that only a very small coupling
($\beta\sim\mathcal{O}(10^{-3})$) can survive in current RSD data. However, all
these analyses had to assume $w>-1$ and $\beta>0$ due to the existence of the
large-scale instability in the IDE scenario. In our recent work [Phys. Rev. D
90, 063005 (2014)], we successfully solved this large-scale instability problem
by establishing a parametrized post-Friedmann (PPF) framework for the IDE
scenario. So we, for the first time, have the ability to explore the full
parameter space of the IDE models. In this work, we reexamine the observational
constraints on the $Q=3\beta H\rho_{de}$ model within the PPF framework. By
using the Planck data, the baryon acoustic oscillation data, the JLA sample of
supernovae, and the Hubble constant measurement, we get
$\beta=-0.010^{+0.037}_{-0.033}$ ($1\sigma$). The fit result becomes
$\beta=-0.0148^{+0.0100}_{-0.0089}$ ($1\sigma$) once we further incorporate the
RSD data in the analysis. The error of $\beta$ is substantially reduced with
the help of the RSD data. Compared with the previous results, our results show
that a negative $\beta$ is favored by current observations, and a relatively
larger interaction rate is permitted by current RSD data.
