Direct measurements of the speed of gravitational waves using the Decihertz Interferometer Gravitational Wave Observatory

This is the authors' abstract. We don't add key points for this paper.

In this Letter, we propose a new model-independent strategy for a direct measurement of the speed of gravitational waves v g based on the DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO), a future Japanese space gravitational-wave antenna. Our methodology leverages DECIGO’s ability to measure the cosmological distance D L ( z ) and the cosmic expansion rate H ( z ) at the same redshift. Each binary neutron star (BNS) inspiral creates a valuable opportunity for a direct measurement of the speed of gravitational waves (GWs) at different redshifts and directions in the sky. In the DECIGO low-frequency band, observation of BNSs during a one-year mission would produce robust measurements of the absolute value of v g with an accuracy at the 10 −5 level. Such assessments of v g in the low-frequency domain improve by three orders of magnitude over other direct methods based on ground-based GW detectors (in the high-frequency domain). If General Relativity is not the ultimate theory of gravity, DECIGO will provide the evidence of its failure through a one-year observation of BNS events.