New parametrization for unified dark matter and dark energy

Abstract

In this paper, we investigate a new phenomenological parametrization for unified dark matter and dark energy based on the polynomial expansion of the barotropic equation of state parameter $w$. Our parametrization provides a well-behaving evolution of $w$ for both small and big redshifts as well as in the far future. The dark fluid described by our parametrization behaves for big redshifts like dark matter (DM). Therefore, one can parametrize dark energy and dark matter using a single dark fluid, like in the case of the Chaplygin gas. Within this parametrization, we consider two models: one with a dark energy (DE) barotropic parameter fixed to be $\ensuremath{-}1$ and the second one, where $w\ensuremath{\ne}\ensuremath{-}1$ is chosen to match the best fit to the data. We study the main cosmological properties of these models at the expansion and perturbation levels. Based on the Markov chain Monte Carlo method with the currently available cosmic observational data sets, we constrain these models to determine the cosmological parameters at the level of the background and clustering of matter. We consider the interaction between dark matter and dark energy which directly affects the evolution of matter and its clustering. Our model appears to be perfectly consistent with the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, while providing unification of DE and DM.