Unique Multimessenger Signal of QCD Axion Dark Matter

Abstract

We propose a multi-messenger probe of the natural parameter space of QCD axion dark matter based on observations of black hole-neutron star binary inspirals. It is suggested that a dense dark matter spike may grow around intermediate mass black holes (10 3 − 10 5 M ). The presence of such a spike produces two unique effects: a distinct phase shift in the gravitational wave strain during the inspiral and a enhancement of the radio emission due to the resonant axion-photon conversion occurring in the neutron star magnetosphere throughout the inspiral and merger. Remarkably, the observation of the gravitational wave signal can be used to infer the dark matter density and, consequently, to predict the radio emission. We study the projected sensitivity to the axion-photon coupling in the light of the LISA interferometer and next-generation radio telescopes such as the Square Kilometre Array. Given a sufficiently nearby detection, such observations will explore the QCD axion in the mass range 10 −7 eV to 10 −5 eV.

Detecting dark matter around black holes with gravitational waves: Effects of dark-matter dynamics on the gravitational waveform

“…We therefore neglect the gravitational potential due to the DM halo and write ΨðrÞ ¼ Gm 1 =r (see, e.g., Appendix II of Ref. [50] for a numerical comparison). This also allows us to assume that the DM halo evolves in a fixed gravitational potential, rather than having to update the potential as the DM halo is perturbed.…”

“…For a given density profile ρðrÞ, the distribution function fðEÞ can be recovered using the Eddington inversion procedure [ [46] p. 290]. The initial equilibrium distribution function of the power-law spike is given by [50]:…”

Gravitational wave probes of dark matter: challenges and opportunities

“…3.1) leading to an even larger predicted signal in NS-IMBH binaries. GW observations of such a system could provide a measurement of the DM density (through the dephasing effect), fixing the normalization of the expected radio signal [132]. Joint observations of these systems using LISA and the Square Kilometer Array [133] would thus probe the natural parameter space of the QCD axion in the mass range m a ∈ [10 −7 , 10 −5 ] eV.…”

“…Axion forces [178] QCD Axion (GW/Radio) [132] EMRI dephasing [111,112] Axion DM [204] Bubble collision DM [289] Rolling axions [246] Dark Photon DM [202] Dark blobs [195] PBH mergers [56,62] BH-boson condensate [121,122] Hidden-sector scalars [279,280] BH spin distribution [121,122] Boson stars [157,158,163,166] PBH/sub-halo transits [228,229] Figure 2: Summary of possible gravitational wave constraints on dark matter.…”

Radio line properties of axion dark matter conversion in neutron stars

“…Historically, these ideas can be dated to a proposal by Pshirkov and Popov [34], while the more general question of mixing of axions with photons in neutron star magnetospheres was also considered in [35]. More recently, the subject has seen a renewed interest [16,[36][37][38][39][40][41].…”