Polarization Modes of Gravitational Waves in Palatini Horndeski theory

TL;DR

This paper investigates the polarization modes of gravitational waves within Palatini Horndeski gravity, revealing diverse scalar modes depending on parameters, with implications for future gravitational wave detection.

Contribution

It provides a detailed analysis of gravitational wave polarization modes in Palatini Horndeski theory, highlighting parameter-dependent scalar modes and their potential detectability.

Findings

All cases have + and × modes propagating at light speed.

Scalar modes vary from 0 to 2 degrees of freedom depending on parameters.

No vector modes are present in any case.

Abstract

In this paper, the polarization modes of gravitational waves in Horndeski gravity are studied under the Palatini formalism. After obtaining the linearized equation of perturbations in Minkowski background, we find that the polarization modes of gravitational waves depend on the selection of the theoretical parameters. The polarization modes can be divided into quite rich cases by parameters. In all cases of parameter selection, there are $+$ and $\times$ modes propagating at the speed of light but no vector modes. The only difference from general relativity is scalar modes, especially the scalar degrees of freedom can be 0, 1 or 2 in different cases. The appropriate parameter cases can be expected to be selected in the detection of gravitational wave polarization modes by Lisa, Taiji and TianQin in the future.