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This theoretical study examines how axion dark matter particles can accumulate around primordial black holes through self-interactions, forming dense "clouds" in specific parameter ranges where quantum enhancement outpaces cosmological expansion. The researchers derive conditions for when these clouds can form and persist, and propose two observational signatures: radio emission from axions converting to photons near neutron stars, potentially detectable by facilities like VLA and ALMA, and modifications to gravitational microlensing patterns when cloud sizes approach the scale of the lensing effect.
Why it matters
If confirmed, this work provides a novel method to detect both axion dark matter and primordial black holes simultaneously through astronomical observations. The predicted radio signals and microlensing anomalies offer concrete, testable predictions that could help solve two major mysteries in physics: the nature of dark matter and the existence of primordial black holes.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: We study the stimulated capture of axion and axion-like particles around primordial black holes, mediated by quartic self-interactions. We identify the parametric regions where Bose-enhanced growth overcomes cosmological dilution and derive analytic criteria for efficient formation and long-term survival of the hydrogenic ground-state cloud, confronting them with current bounds on axion-photon couplings. We discuss observational implications of these PBH+cloud systems, including resonant axion-to-photon conversion in neutron star magnetospheres and finite-size microlensing distortions. In the former case, the resonance condition selects a conversion shell outside the neutron star surface, and we show that the large axion occupation number of the cloud can compensate for the small conversion probability. The resulting transient line flux densities can exceed nominal VLA and ALMA sensitivities in regions where the Galactic encounter rate is observationally relevant. Independently, when the cloud size becomes comparable to or larger than the Einstein radius, finite-size effects can modify the standard point-lens microlensing light curve.
Source: Stimulated capture of axion dark matter around primordial black holes