Constraining the gravitational coupling of axion dark matter at LIGO
Sunghoon Jung (Center for Theoretical Physics, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea); TaeHun Kim (Center for Theoretical Physics, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea); Jiro Soda (Department of Physics, Kobe University, Kobe 657-8501, Japan); Yuko Urakawa (Department of Physics and Astrophysics, Nagoya University, Chikusa, Nagoya 464-8602, Japan, Fakultüt für Physik, Universität Bielefeld, Bielefeld 33501, Germany)
The axion-gravity Chern-Simons coupling is well motivated but is relatively weakly constrained, partly due to difficult measurements of gravity. We study the sensitivity of LIGO measurements of chirping gravitational waves (GWs) on such coupling. When the frequency of the propagating GW matches with that of the coherent oscillation of axion dark matter field, the decay of axions into gravitons can be stimulated, resonantly enhancing the GW. Such a resonance peak can be detected at LIGO as a deviation from the chirping waveform. Since all observed GWs will undergo similar resonant enhancement from the Milky Way (MW) axion halo, LIGO observations can potentially provide the strongest constraint on the coupling, at least for the axion mass . Along the course, we also emphasize the relevance of the finite coherence of axion fields and the ansatz separating forward and backward propagations of GWs. As a result, the parity violation of the Chern-Simons coupling is not observable from chirping GWs.
