Dark energy, cosmic coincidence and future singularity of the universe

Abstract

Dark energy model with the equation of state $p_{DE} =-\rho _{DE} -A\rho _{DE}^\alpha$, is characterised by four finite life time future singularity of the universe for different values of the parameter $A$ and $\alpha$ [Nojiri et al. in Phys Rev D 71:063004, 2005]. Since from the matter dominated era to the dark energy dominated era the ratio of the dark energy density to the matter energy density increases as the universe expand for these future singularities, the universe passes through a significant time when the dark energy density and the matter energy density are nearly comparable. Considering $\frac{1}{r_0 }<r=\frac{\rho _{DE} }{\rho _M }<r_0$, where $r_0$ is any fixed ratio, we calculate the fraction of total life time of the universe when the universe passes through the coincidental stage for these singularities. It has been found that the fractional time varies as $\alpha$ varies within the range for which these finite life time future singularities occur and the fraction is smaller for smaller values of $r_0$. Importance of the fractional time and observational limits onto the values of the parameter $A$ and $\alpha$ has also been discussed.