Elina Palmgren (Helsinki institute of physics, Finland)
This presentation will introduce the research  in which we employed the Planck 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 assumed time-dependent equation of state parameter for dark energy, and treated 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, the BAO data break this degeneracy. As a novelty 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. In models with $w<-1$ the CMB and BAO data favour energy transfer from dark energy to dark matter at the rate of about 35\% of today's Hubble rate while the non-interacting model is 3$\sigma$ "disfavoured" by these data. Adding the CMB lensing data to the constraint budget, restores the non-interacting model to or near to the border of the 68\% CL region. References  J.Valiviita, E. Palmgren. arXiv:1504.02464. Accepted for publication in JCAP (2015).