Distinguishing interacting dark energy from wCDM with CMB, lensing, and
  baryon acoustic oscillation data
  We employ the Planck 2013 CMB temperature anisotropy and lensing data, and
baryon acoustic oscillation (BAO) data to constrain a phenomenological $w$CDM
model, where dark matter and dark energy interact. We assume time-dependent
equation of state parameter for dark energy, and treat dark matter and dark
energy as fluids whose energy-exchange rate is proportional to the dark-matter
density. The CMB data alone leave a strong degeneracy between the interaction
rate and the physical CDM density parameter today, $\omega_c$, allowing a large
interaction rate $|\Gamma| \sim H_0$. However, as has been known for a while,
the BAO data break this degeneracy. Moreover, we exploit the CMB lensing
potential likelihood, which probes the matter perturbations at redshift $z \sim
2$ and is very sensitive to the growth of structure, and hence one of the tools
for discerning between the $\Lambda$CDM model and its alternatives. However, we
find that in the non-phantom models ($w_{\mathrm{de}}>-1$), the constraints
remain unchanged by the inclusion of the lensing data and consistent with zero
interaction, $-0.14 < \Gamma/H_0 < 0.02$ at 95\% CL. On the contrary, in the
phantom models ($w_{\mathrm{de}}<-1$), energy transfer from dark energy to dark
matter is moderately favoured over the non-interacting model; $-0.57 <
\Gamma/H_0 < -0.10$ at 95\% CL with CMB+BAO, while addition of the lensing data
shifts this to $-0.46 < \Gamma/H_0 < -0.01$.
