Cosmology with interaction between phantom dark energy and dark matter and thecoincidence problem

Abstract

We study a cosmological model in which phantom dark energy is coupled to dark matter byphenomenologically introducing a coupled term to the equations of motion of dark energyand dark matter. This term is parameterized by a dimensionless coupling functionδ, theHubble parameter and the energy density of dark matter, and it describes an energy flow betweenthe dark energy and dark matter. We discuss two cases: one is the case where the equation of stateωe of the dark energy is a constant; the other is that where the dimensionless coupling functionδ is a constant. We investigate the effect of the interaction on the evolution of theuniverse, the total lifetime of the universe and the ratio of the period when theuniverse is in the coincidence state to its total lifetime. It turns out that theinteraction will produce significant deviation from the case without the interaction.