Tsunamis and Ripples: Effects of Scalar Waves on Screening in the Milky Way

TL;DR

This paper investigates the impact of scalar waves in modified gravity models with screening mechanisms, finding that such waves generally do not significantly affect Solar System tests, thus supporting the models' viability.

Contribution

It provides a quantitative analysis of scalar wave effects in symmetron and chameleon models, demonstrating their negligible impact on Solar System screening.

Findings

Scalar waves have negligible effects in symmetron models.

Propagating waves do not significantly affect chameleon screening.

Focusing wave energy on the Solar System would be required to disrupt screening.

Abstract

Modified gravity models which include an additional propagating degree of freedom are typically studied in the quasi-static limit, where the propagation is neglected, and the wave equation of the field is replaced with a Poisson-type equation. Recently, it has been proposed that, in the context of models with symmetron- or chameleon-type screening, scalar waves from astrophysical or cosmological events could have a significant effect on the screening of the Solar System, and hence invalidate these models. Here, we quantitatively investigate the impact of scalar waves by solving the full field equation linearised in the wave amplitude. In the symmetron case, we find that the quantitative effect of waves is generally negligible, even for the largest amplitudes of waves that are physically expected. In order to spoil the screening in the Solar System, a significant amount of wave energy would have to be focused on the Solar System by arranging the sources in a spherical shell centred on Earth. In the chameleon case, we are able to rule out any significant effects of propagating waves on Solar System tests.