Can dark matter\u2013dark 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 _xpropto 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 wne -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 wne -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 =-0.075pm 0.046 at 68% C.L.. In this case we find that the CP is not alleviated even for 2sigma interval for alpha . Furthermore, this last model is discarded against flat Lambda CDM according to BIC analysis.