Intrinsic Solar System decoupling of a scalar-tensor theory with a universal coupling between the scalar field and the matter Lagrangian

TL;DR

This paper introduces a class of scalar-tensor theories with a universal matter coupling that naturally decouples the scalar field from matter in the Solar System, aligning with general relativity predictions but with detectable deviations in gravitational redshift.

Contribution

The paper proposes a new class of Brans-Dicke-like theories with a universal coupling that results in Solar System phenomenology nearly identical to general relativity, with potential observable deviations in gravitational redshift.

Findings

Decoupling mechanism reduces scalar field effects in the Solar System.

Trajectories and light propagation match general relativity at second post-Newtonian order.

Future missions could detect deviations in gravitational redshift predicted by these theories.

Abstract

In this communication, we present a class of Brans-Dicke-like theories with a universal coupling between the scalar field and the matter Lagrangian. We show this class of theories naturally exhibits a decoupling mechanism between the scalar field and matter. As a consequence, this coupling leads to almost the same phenomenology as general relativity in the Solar System: the trajectories of massive bodies and the light propagation differ from general relativity only at the second post-Newtonian order. Deviations from general relativity are beyond present detection capabilities. However, this class of theories predicts a deviation of the gravitational redshift at a level detectable by the future ACES and STE/QUEST missions.