Testing screened scalar-tensor theories of gravity with atomic clocks

TL;DR

This paper explores the potential of using atomic clock gravitational redshift measurements to test screened scalar-tensor theories of gravity, offering a new approach beyond traditional fifth force experiments.

Contribution

It introduces a novel method for testing screened scalar-tensor models via gravitational redshift measurements with atomic clocks, including a proposed thought experiment for the chameleon model.

Findings

Future redshift experiments could constrain currently untested chameleon parameter space.

The derived redshift expression enables new experimental tests of scalar-tensor theories.

Laboratory and space-based setups are considered for practical implementation.

Abstract

In any scalar-tensor theory of gravity exhibiting a screening mechanism, the fifth force mediated by the scalar field is dynamically suppressed at sub-Solar system scales, allowing it to pass existing tests of gravity. As a result, a major research effort has been carried out over the past decades to `outsmart' screened scalars in this game of hide-and-seek. While most of such tests rely on fifth force effects, one should keep in mind that the latter are by no means the only physical feature of scalar-tensor gravity. In particular, this article investigates the possibility of testing screened scalar-tensor models by means of gravitational redshift measurements performed with atomic clocks. Upon deriving the expression for the redshift in this framework, we propose a thought experiment for testing the chameleon model by clock comparisons, which guides us towards more realistic experimental setups, in the laboratory and in space. We find that currently unconstrained regions of the chameleon parameter space could be ruled out by future redshift experiments.