Coupling dark energy to dark matter inhomogeneities

TL;DR

This paper explores a model where dark energy couples to dark matter inhomogeneities, naturally triggering cosmic acceleration without fine-tuned initial conditions, and demonstrates its viability through numerical simulations.

Contribution

It introduces a phenomenological coupling between dark energy and dark matter based on the growth function, providing a natural explanation for the onset of acceleration without fine tuning.

Findings

Viable cosmology with radiation, matter, and dark energy eras

Dark energy density depends on coupling parameters, not initial conditions

Model avoids the coincidence problem and fine tuning

Abstract

We propose that dark energy in the form of a scalar field could effectively couple to dark matter inhomogeneities. Through this coupling energy could be transferred to/from the scalar field, which could possibly enter an accelerated regime. Though phenomenological, this scenario is interesting as it provides a natural trigger for the onset of the acceleration of the universe, since dark energy starts driving the expansion of the universe when matter inhomogeneities become sufficiently strong. Here we study a possible realization of this idea by coupling dark energy to dark matter via the linear growth function of matter perturbations. The numerical results show that it is indeed possible to obtain a viable cosmology with the expected series of radiation, matter and dark-energy dominated eras. In particular, the current density of dark energy is given by the value of the coupling parameters rather than by very special initial conditions for the scalar field. In other words, this model - unlike standard models of cosmic late acceleration - does not suffer from the so-called "coincidence problem" and its related fine tuning of initial conditions.