Exploring the spin of ultralight dark matter with gravitational wave detectors

We propose a novel method for distinguishing the spin of ultralight dark matter (ULDM) using interferometric gravitational wave detectors. ULDM can be a bosonic field of spin -0, 1, or 2, and each induces distinctive signatures in signals. We find that the finite -time traveling effect causes a dominant signal for spin -0 and spin -1 ULDM, but not for spin -2. By using overlap reduction functions (ORF) of multiple detectors, we can differentiate between the spins of ULDM. Furthermore, we point out that the current constraint on the coupling constant of spin -1 ULDM to baryons becomes 30 times weaker when the finite -time light -travel effect on the ORF is taken into account.