Gravitational Signatures of Axion Dark Matter via Parity-Violating Interactions

Abstract

We investigate axion-like particles coupled to gravity through a parity-violating Chern-Simons (CS) interaction. In this framework, axion dark matter (DM) can decay into pairs of circularly polarized gravitons, producing a persistent, nearly monochromatic GW signal. We compute the expected signal at Earth assuming a Navarro-Frenk-White Galactic halo model with the corresponding velocity distribution, and compare it with the narrowband sensitivities of the LIGO O4 run and the projected reach of the Einstein Telescope. The resulting bounds on the axion-graviton coupling $\alpha$ improve upon the cosmological stability requirement for axion masses $m_{\varphi }\lesssim 10^{-11}$ eV, excluding values up to four orders of magnitude below the stability limit. This constitutes a robust direct terrestrial constraint on the axion-gravity CS coupling. We also discuss distinctive observational signatures, such as circular polarization asymmetries, annual modulation, and potential enhancements from DM substructures, which could serve as smoking-gun evidence for parity-violating gravitational interactions.

8 pages, 1 figure. COST Actions CA21106 and CA21136

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Cited by in corpus (3)

• The new generation lunar gravitational wave detectors: sky map resolution and joint analysis
• Cosmology of Gravi-Axions
• Beyond general relativity: gravitational waves in non-minimally coupled theories