Dark Energy, scalar-curvature couplings and a critical acceleration scale

TL;DR

This paper explores a scalar field coupled to curvature terms that can evade fifth-force constraints and produce a modified acceleration scale, potentially addressing dark matter small-scale issues and relating to MOND.

Contribution

It introduces a model where curvature couplings create an effective mass, suppressing fifth-force effects and generating a critical acceleration scale linked to the Hubble constant.

Findings

The model passes experimental bounds on fifth forces.

A long-range force appears below a fixed acceleration scale.

The effective mass increases in high-curvature regions.

Abstract

We study the effects of coupling a cosmologically rolling scalar field to higher order curvature terms. We show that when the strong coupling scale of the theory is on the 10^{-3}-10^{-1}eV range, the model passes all experimental bounds on the existence of fifth forces even if the field has a mass of the order of the Hubble scale in vacuum and non-suppressed couplings to SM fields. The reason is that the coupling to certain curvature invariant acts as an effective mass that grows in regions of large curvature. This prevents the field from rolling down its potential near sources and makes its effects on fifth-force search experiments performed in the laboratory to be observable only at the sub-mm scale. We obtain the static spherically symmetric solutions of the theory and show that a long-range force appears but it is turned on only below a fixed Newtonian acceleration scale of the order of the Hubble constant. We comment on the possibility of using this feature of the model to alleviate the CDM small scale crisis and on its possible relation to MOND.