Can a "pure vector" gravitational wave mimic a "pure tensor" one?

TL;DR

This paper explores whether a hypothetical pure vector gravitational wave can produce signals indistinguishable from the standard tensor waves of general relativity when the polarization rotates, challenging the uniqueness of GR's polarization signatures.

Contribution

It demonstrates that a pure vector gravitational wave with rotating polarization can mimic the strain signals of tensor waves in certain detector configurations.

Findings

Pure vector waves can replicate GR tensor wave signals under specific conditions.

Rotating polarization allows degeneracy in detector responses.

Implications for gravitational wave polarization tests.

Abstract

In the general theory of relativity, gravitational waves have two possible polarizations, which are transverse and traceless with helicity $\pm 2$. Some alternatives theories contain additional helicity $0$ and helicity $\pm 1$ polarization modes. Here, we consider a hypothetical "pure vector" theory in which gravitational waves have only two possible polarizations, with helicity $\pm 1$. We show that if these polarizations are allowed to rotate as the wave propagates, then for certain source locations on the sky, the strain outputs of three ideal interferometric gravitational wave detectors can exactly reproduce the strain outputs predicted by general relativity.