| 1. |
- Edwards, Thomas D. P., et al.
(author)
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Transient Radio Signatures from Neutron Star Encounters with QCD Axion Miniclusters
- 2021
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 127:13
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Journal article (peer-reviewed)abstract
- The QCD axion is expected to form dense structures known as axion miniclusters if the Peccei-Quinn symmetry is broken after inflation. Miniclusters that have survived until today will interact with neutron stars (NSs) in the Milky Way to produce transient radio signals from axion-photon conversion in the NS magnetosphere. We quantify the properties of these encounters and find that they occur frequently [O(1–100)day−1], last between a day and a few months, are spatially clustered toward the Galactic Center, and can reach observable fluxes. These radio transients are within reach of current generation telescopes and therefore offer a promising pathway to discovering QCD axion dark matter
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| 2. |
- Kavanagh, Bradley J., et al.
(author)
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Stellar disruption of axion miniclusters in the Milky Way
- 2021
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 104:6
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Journal article (peer-reviewed)abstract
- Axion miniclusters are dense bound structures of dark matter axions that are predicted to form in the postinflationary Peccei-Quinn symmetry breaking scenario. Although dense, miniclusters can easily be perturbed or even become unbound by interactions with baryonic objects such as stars. Here, we characterize the spatial distribution and properties of miniclusters in the Milky Way (MW) today after undergoing these stellar interactions throughout their lifetime. We do this by performing a suite of Monte Carlo simulations which track the miniclusters’ structure and, in particular, accounts for partial disruption and mass loss through successive interactions. We consider two density profiles—Navarro-Frenk-White (NFW) and power-law (PL)—for the individual miniclusters in order to bracket the uncertainties on the minicluster population today due to their uncertain formation history. For our fiducial analysis at the solar position, we find a survival probability of 99% for miniclusters with PL profiles and 46% for those with NFW profiles. Our work extends previous estimates of this local survival probability to the entire MW. We find that towards the Galactic Center, the survival probabilities drop drastically. Although we present results for a particular initial halo mass function, our simulations can be easily recast to different models using the provided data and code (github.com/bradkav/axion-miniclusters). Finally, we comment on the impact of our results on lensing, direct, and indirect detection.
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| 3. |
- Witte, Samuel J., et al.
(author)
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Axion-photon conversion in neutron star magnetospheres : The role of the plasma in the Goldreich-Julian model
- 2021
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 104:10
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Journal article (peer-reviewed)abstract
- The most promising indirect search for the existence of axion dark matter uses radio telescopes to look for narrow spectral lines generated from the resonant conversion of axions in the magnetospheres of neutron stars. Unfortunately, a large list of theoretical uncertainties has prevented this search strategy from being fully accepted as robust. In this work we attempt to address major outstanding questions related to the role and impact of the plasma, including: (i) does refraction and reflection of radio photons in the magnetosphere induce strong inhomogeneities in the flux, (ii) can refraction induce premature axion-photon dephasing, (iii) to what extent do photon-plasma interactions induce a broadening of the spectral line, (iv) does the flux have a strong time dependence, and (v) can radio photons sourced by axions be absorbed by the plasma. We present an end-to-end analysis pipeline based on ray-tracing that exploits a state-of-the-art auto-differentiation algorithm to propagate photons from the conversion surface to asymptotically large distances. Adopting a charge symmetric Goldreich-Julian model for the magnetosphere, we show that for reasonable parameters one should expect a strong anisotropy of the signal, refraction induced axion-photon dephasing, significant line-broadening, a variable time-dependence of the flux, and, for large enough magnetic fields, anisotropic absorption. Our simulation code is flexible enough to serve as the basis for follow-up studies with a large range of magnetosphere models.
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