Distinguishing gravity theories with networks of space-based gravitational-wave detectors

Abstract

We propose a method for separating and detecting the non-tensor modes of stochastic gravitational-wave backgrounds (SGWBs) using networks of space-based gravitational-wave detectors. We consider four distinct data-reconstruction schemes for the co-inclination and anti-inclination orbital configurations of the LISA-Taiji network. We find that the co-inclination configuration offers its advantages over the anti-inclination one and can achieve signal-to-noise ratios up to 17.3 for the vector modes and 10.4 for the scalar modes with the energy density spectrum as $Ω_{GW}^p(f)=10^{-12}$. Our method can be used to measure beyond-general-relativity polarization modes of SGWBs at mHz frequency band, opening a new avenue for testing alternative gravity theories.

Figures (4)

• Figure 1: The upper picture is a schematic of the LISA and Taiji constellations relative to the Earth’s orbit. The blue curve shows the Earth’s orbit around the Sun, with LISA trailing the Earth by $\sim20^\circ$ and Taiji leading by $\sim20^\circ$.The lower picture shows the inclination of the constellation planes relative to the ecliptic.
• Figure 2: Top‐down deformation of a unit ring by the six independent gravitational‐wave polarizations: tensor-plus and tensor-cross in the X–Y plane; vector-x in X–Z and vector-y in Y–Z; scalar “breathing” in X–Y; and scalar “longitudinal” along Z (identical when viewed from X or Y). Solid and dashed curves show the two quadrature phases.
• Figure 3: The effective ORF $\Gamma$ of the reconstructed data. The first picture shows the ORF for vector polarization of the anti-inclination LISA-Taiji network, the second one shows the ORF for vector polarization of the co-inclination network, the third one shows the ORF for scalar polarization of the anti-inclination network, and the last one shows the ORF for scalar polarization of the co-inclination network.
• Figure 4: The sensitivity curves of the reconstructed data. The first picture shows the sensitivity curves for vector polarization of the anti-inclination LISA-Taiji network, the second one shows the sensitivity curves for vector polarization of the co-inclination network, the third one shows the sensitivity curves for scalar polarization of the anti-inclination network, and the last one shows the sensitivity curves for scalar polarization of the co-inclination network.