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 _ { 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 _ { 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 .