Constraints on scalar-tensor models of dark energy from observational and local gravity tests

TL;DR

This paper develops scalar-tensor dark energy models compatible with local gravity tests and observations, showing that a chameleon mechanism allows for significant scalar-matter coupling while fitting cosmological data.

Contribution

It introduces a family of scalar-tensor dark energy models with constant coupling, compatible with local gravity constraints via a chameleon mechanism, and analyzes their observational signatures.

Findings

Models can satisfy local gravity constraints with |Q| ~ 1 using chameleon mechanism.

Equation of state of dark energy diverges at smaller redshifts as deviation from LambdaCDM increases.

Bounds on coupling |Q| and model parameters are derived from matter power spectrum and CMB data.

Abstract

We construct a family of viable scalar-tensor models of dark energy (DE) which possess a phase of late-time acceleration preceded by a standard matter era, while at the same time satisfying the local gravity constraints (LGC). The coupling Q between the scalar field and the non-relativistic matter in the Einstein frame is assumed to be constant in our scenario, which is a generalization of f(R) gravity theories corresponding to the coupling Q=-1/sqrt{6}. We find that these models can be made compatible with local gravity constraints even when |Q| is of the order of unity through a chameleon mechanism, if the scalar-field potential is chosen to have a sufficiently large mass in the high-curvature regions. We show that these models generally lead to the divergence of the equation of state of DE, which occur at smaller redshifts as the deviation from the LambdaCDM model become more significant. We also study the evolution of matter density perturbations and employ them to place bounds on the coupling |Q| as well as model parameters of the field potential from observations of the matter power spectrum and the CMB anisotropies. We find that, as long as |Q| is smaller than the order of unity, there exist allowed parameter regions that are consistent with both observational and local gravity constraints.