Dark radiation and dark matter coupled to holographic Ricci dark energy

TL;DR

This paper models a universe with interacting dark matter, holographic dark energy, and dark radiation, constraining parameters with observational data, and finds the interaction alleviates the cosmic coincidence problem.

Contribution

It introduces a coupled dark energy and dark radiation model with holographic principles, reconstructed via linear interactions and constrained by observational data.

Findings

Excess dark energy during recombination era

Bound on dark energy at big-bang nucleosynthesis

Interaction alleviates the cosmic coincidence problem

Abstract

We investigate a universe filled with interacting dark matter, holographic dark energy, and dark radiation for the spatially flat Friedmann-Robertson-Walker (FRW) spacetime. We use a linear interaction to reconstruct all the component energy densities in terms of the scale factor by directly solving the balance's equations along with the source equation. We apply the $\chi^{2}$ method to the observational Hubble data for constraining the cosmic parameters, contrast with the Union 2 sample of supernovae, and analyze the amount of dark energy in the radiation era. It turns out that our model exhibits an excess of dark energy in the recombination era whereas the stringent bound $\Omega_{\rm x}(z\simeq 10^{10})<0.21$ at big-bang nucleosynthesis is fulfilled. We find that the interaction provides a physical mechanism for alleviating the triple cosmic coincidence and this leads to $\Omega_{\rm m0}/\Omega_{\rm x0} \simeq \Omega_{\rm r0}/\Omega_{\rm x0} \simeq {\cal O}(1)$.