Can dark matter-dark energy interaction alleviate the Cosmic Coincidence Problem?

Abstract

In this paper we study a model of interacting dark energy - dark matter where the ratio between these components is not constant, changing from early to late times in such a way that the model can solve or alleviate the cosmic coincidence problem (CP). The interaction arises from an assumed relation of the form ${\rho }_x\propto {\rho }_d^{\alpha }$, where ${\rho }_x$ and ${\rho }_d$ are the energy densities of dark energy and dark matter components, respectively, and $\alpha$ is a free parameter. For a dark energy equation of state parameter $w=-1$ we found that, if $\alpha =0$, the standard $\Lambda$CDM model is recovered, where the coincidence problem is unsolved. For $0<\alpha <1$, the CP would be alleviated and for $\alpha \sim 1$, the CP would be solved. The dark energy component is analyzed with both $w=-1$ and $w\ne -1$. Using Supernovae type Ia and Hubble parameter data constraints, in the case $w=-1$ we find $\alpha =0.109_{-0.072}^{+0.062}$ at 68% C.L., and the CP is alleviated. For $w\ne -1$, a degeneracy arises on the $w$ - $\alpha$ plane. In order to break such degeneracy we add cosmic microwave background distance priors and baryonic acoustic oscillations data to the constraints, yielding $\alpha =-0.075\pm 0.046$ at 68% C.L.. In this case we find that the CP is not alleviated even for 2$\sigma$ interval for $\alpha$. Furthermore, this last model is discarded against flat $\Lambda$CDM according to BIC analysis.

22 pages, 6 figures, revised version, with Bayesian Information Criterion (BIC) analysis included. Version published

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