Solar System Constraints on Disformal Gravity Theories

TL;DR

Disformal gravity theories, which involve derivative couplings of scalar fields to matter, are tightly constrained by solar system tests, significantly limiting their cosmological relevance.

Contribution

We derived the PPN parameters for disformal gravity theories and established the strongest solar system constraints to date, limiting their impact on cosmology.

Findings

Constraints on disformal coupling scale: rom ew eV to ew hundred eV

Solar system tests exclude significant disformal effects in cosmology

Disformal effects are rendered irrelevant for cosmological models

Abstract

Disformal theories of gravity are scalar-tensor theories where the scalar couples derivatively to matter via the Jordan frame metric. These models have recently attracted interest in the cosmological context since they admit accelerating solutions. We derive the solution for a static isolated mass in generic disformal gravity theories and transform it into the parameterised post-Newtonian form. This allows us to investigate constraints placed on such theories by local tests of gravity. The tightest constraints come from preferred-frame effects due to the motion of the Solar System with respect to the evolving cosmological background field. The constraints we obtain improve upon the previous solar system constraints by two orders of magnitude, and constrain the scale of the disformal coupling for generic models to $\mathcal{M} \gtrsim 100$ eV. These constraints render all disformal effects irrelevant for cosmology.