Can we have a stringy origin behind $\Omega_\Lambda(t)\propto \Omega_m(t)$?

TL;DR

This paper proposes a string-inspired phenomenological model explaining the observed ratio of dark energy to matter density, the small cosmological constant, and recent cosmic acceleration through radion/dilaton dynamics.

Contribution

It introduces a higher-dimensional physics motivated model where radion/dilaton fields cause the dark energy density to track matter density and dominate recently.

Findings

Radion/dilaton couplings differ for standard model and dark matter.

The model explains the near-equality of dark energy and matter densities today.

Cosmic acceleration is a recent consequence of radion/dilaton dynamics.

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.