Coupled quintessence and the coincidence problem

Abstract

We consider a model of interacting cosmological constant/quintessence, where dark matter and dark energy behave as, respectively, two coexisting phases of a fluid, a thermally excited Bose component and a condensate, respectively. In a simple phenomenological model for the dark components interaction we find that their energy density evolution is strongly coupled during the universe evolution. This feature provides a possible way out for the coincidence problem affecting many quintessence models.

Figures (11)

• Figure 1: Energy densities in unit of $\rho _{c_{0}}$ for $\alpha =1$, $\beta =0$ and $\lambda =-0.001$.
• Figure 2: Energy densities in unit of $\rho _{c_{0}}$ for $\alpha=1$ and $\lambda=-0.001$ and varying $\beta$; the corresponding value of $\beta$ is reported on the top of each graph.
• Figure 3: Energy densities in unit of $\rho _{c_{0}}$ for $\lambda =0$, $-0.001$ with $\alpha =1$ and $\beta =1$.
• Figure 4: The $\log_{10}\left[\tilde{\rho}_m /\tilde{\rho}_\Lambda\right]$ versus $x$ for the two values $\beta=0.6$ (Fig.(a)) and $\beta=0.9$ (Fig.(b)). The values of $\alpha$ and $\lambda$ are the same of Figure \ref{['variabeta']}.
• Figure 5: Energy densities in unit of $\rho _{c_{0}}$ for varying $\lambda$; the corresponding value of $\lambda$ is reported on the top of each graph. The quantities $\alpha$ and $\beta$ are both fixed to be equal to $1$.