Assuming a nongravitational interaction among the dark fluids of our Universe—namely, dark matter and dark energy—we study a specific interaction model in the background of a spatially flat Friedmann-Lemaître-Robertson-Walker geometry. We find that the interaction model solves the background evolution in an analytic way when the dark energy takes a constant barotropic equation of state, $w_x$. In particular, we analyze two separate interaction scenarios, namely, when the dark energy is a fluid other than the vacuum energy (i.e., $w_x\ne -1$) and when it is vacuum energy itself (i.e., $w_x=-1$). We find that the interacting model with $w_x\ne -1$ produces stable perturbations at large scales for $w_x<-1$ with the coupling strength $\xi <0$. Both scenarios are constrained by the latest astronomical data. The analyses show that a very small interaction with the coupling strength is allowed, and within the 68.3% confidence region $\xi =0$ is recovered. The analyses further show that a large coupling strength significantly affects the large-scale dynamics of the Universe, while according to the observational data the interaction models are very well consistent with $\mathrm{\Lambda }$ cosmology. Furthermore, we observe that for the vacuum interaction scenario, the tension on $H_0$ is not released while for the interacting dark energy scenario with $w_x<-1$, the tension on $H_0$ seems to be released partially because of the high error bars in $H_0$. Finally, we conclude the work by calculating the Bayesian evidence, which shows that $\mathrm{\Lambda }\mathrm{CDM}$ cosmology is favored over the two interacting scenarios.

• Received 23 March 2018

DOI:https://doi.org/10.1103/PhysRevD.98.043517