Unifying gravitational waves and dark energy

TL;DR

This paper develops a unified framework for analyzing metric and scalar perturbations in scalar-tensor gravity theories, revealing that high-frequency scalar waves are screened and undetectable, with implications for dark energy and gravitational wave research.

Contribution

It introduces a unified treatment of perturbations across energy regimes and demonstrates the screening of scalar waves in various frequency ranges.

Findings

High-frequency scalar perturbations are not self-consistent under geometric optics.

Scalar waves are screened in both low and high-frequency regimes.

The framework applies to chameleon and symmetron screening mechanisms.

Abstract

We present a unifying treatment for metric and scalar perturbations across different energy regimes in scalar-tensor theories of gravity. To do so, we introduce two connected symmetry-breaking patterns: one due to the acquisition of nontrivial vacuum expectation values by the fields and the other due to the distinction between background and perturbations that live on top of it. We show that the geometric optics approximation commonly used to enforce this separation is not self-consistent for high-frequency perturbations since gauge transformations mix different tensor and scalar sectors orders. We derive the equations of motions for the perturbations and describe the behavior of the solutions in the low and high-frequency limits. We conclude by describing this phenomenology in the context of two screening mechanisms, chameleon and symmetron, and show that scalar waves in every frequency range are screened, hence not detectable.