Can we have a stringy origin behind ${\Omega }_{\Lambda }(t)\propto {\Omega }_m(t)$?

Abstract

Inspired by the current observations that the ratio of the abundance of dark energy ${\Omega }_{\Lambda }$, and the matter density, ${\Omega }_m$, is such that ${\Omega }_m/{\Omega }_{\Lambda }\sim 0.37$, we provide a string inspired phenomenological model where we explain this order one ratio, the smallness of the cosmological constant, and also the recent cosmic acceleration. We observe that any effective theory motivated by a higher dimensional physics provides radion/dilaton couplings to the standard model and the dark matter component with different strengths. Provided radion/dilaton is a dynamical field we show that ${\Omega }_{\Lambda }(t)$ tracks ${\Omega }_m(t)$ and dominates very recently.

Comments: 4 pages, discussions added on recent acceleration, typos corrected, references added