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

TL;DR

This paper investigates an interacting dark energy-dark matter model where the interaction can potentially solve or alleviate the cosmic coincidence problem, using observational data to constrain the model parameters.

Contribution

It introduces a specific interaction model with a power-law relation between dark energy and dark matter densities and constrains it with observational data, assessing its effectiveness in addressing the coincidence problem.

Findings

For w=-1, the model alleviates the coincidence problem with α≈0.109.

Adding CMB and BAO data constrains α near zero, not alleviating the problem.

The model with w≠-1 is disfavored compared to ΛCDM based on BIC analysis.

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 $w \neq -1$. Using Supernovae type Ia and Hubble parameter data constraints, in the case $w=-1$ we find $\alpha=0.109^{+0.062}_{-0.072}$ at 68% C.L., and the CP is alleviated. For $w\neq -1$, 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.