Constraining the Extra Polarization Modes of Gravitational Waves with Double White Dwarfs

TL;DR

This paper evaluates TianQin's ability to detect extra polarization modes of gravitational waves from double white dwarfs, considering various radiation modes and observational configurations, to test alternative gravity theories.

Contribution

It provides a detailed analysis of how TianQin can constrain extra polarization modes using DWD signals, including the effects of source orientation and joint observations.

Findings

TianQin's detection capability strongly depends on source orientation.

ZTF J1539 offers the best constraint among verification binaries.

Joint observation with LISA enhances detection prospects.

Abstract

The detection of gravitational wave (GW) has opened a new window to test the theory of gravity in the strong field regime. In general relativity (GR), GW can only possess two tensor polarization modes, which are known as the $+$ and $\times$ modes. However, vector and scalar modes can exist in some modified theories of gravity, and we can test the gravitational theories by probing these extra polarization modes. As a space-borne GW detector, TianQin will be launched in the 2030s, and it is expected to observe plenty of GW signals, including those from nearly ten-thousands double white dwarfs (DWDs) in our galaxy. This offers an excellent chance for testing the existence of extra polarization modes. In this article, we analyze the capability of detecting the extra polarization modes with DWDs. For the extra modes, we consider both the leading order dipole radiation and the subleading quadrupole radiation. We find that the capability of TianQin has very strong dependency on the source orientation. We also analyze all the verification binaries with determined position and frequency, and find that ZTF J1539 can give the best constraint on the extra polarization modes. We have also considered the case of TianQin twin constellation, and the joint observation with LISA.