Gravitational wave interactions in $\Lambda_3$ models of dark energy

TL;DR

This paper investigates the interactions between scalar and tensor gravitons in $ ext{Lambda}_3$ dark energy models, highlighting potential decay channels and instabilities affecting gravitational waves, with implications for observations like LIGO/Virgo.

Contribution

It identifies the ubiquity of cubic interactions in $ ext{Lambda}_3$ models and discusses their role in gravitational wave decay and instabilities, emphasizing the complexity due to higher order interactions.

Findings

Cubic interactions between scalar and tensor gravitons are common in $ ext{Lambda}_3$ models.

These interactions can cause decay of gravitational waves and gradient instabilities.

Higher order interactions complicate predictions of instability outcomes.

Abstract

We argue that cubic order interactions between two scalar gravitons and one tensor graviton are ubiquitous in models of dark energy where the strong coupling scale is $\Lambda_3$. These interactions can potentially provide efficient decay channels for gravitational waves. They can also lead to gradient instabilities of the scalar perturbations in the presence of large amplitude gravitational waves, e.g. those detected by LIGO/Virgo. In contrast with models in scalar-tensor theories, there is an infinite number of higher order interactions in generic $\Lambda_3$ models, which make it difficult to predict the fate of these instabilities inferred from cubic order interactions.