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Searching for the QCD Axion with Gravitational Microlensing
Malcolm Fairbairn1, David J E Marsh1, Jérémie Quevillon1
1Kings College London, Strand, London, WC2R 2LS, United Kingdom.
Physical Review Letters
|July 29, 2017
Summary
New research uses microlensing data to constrain axion dark matter (DM) production. The study finds the fraction of DM in axion miniclusters is less than 8.3%, offering the first observational limit on this scenario.
Area of Science:
- Cosmology
- Particle Physics
- Astrophysics
Background:
- Axion dark matter (DM) production via phase transitions can generate isocurvature perturbations.
- These perturbations may collapse into dense objects called axion miniclusters.
- Microlensing surveys offer a potential method to detect or constrain these miniclusters.
Purpose of the Study:
- To constrain the axion minicluster scenario using observational microlensing data.
- To determine the fraction of dark matter (DM) that may have collapsed into miniclusters (f_MC).
- To establish the first observational constraints on f_MC for QCD axion models.
Main Methods:
- Computation of the microlensing event rate for spatially extended axion miniclusters.
- Utilization of published microlensing event rate bounds from the EROS survey and Subaru Hyper Suprime Cam.
- Derivation of upper limits on the minicluster fraction (f_MC) based on event rate constraints.
Main Results:
- The first observational constraint on the minicluster fraction is established: f_MC < 0.083 (m_a / 100 μeV)^0.12 for QCD axions.
- Future observations with Subaru could constrain f_MC down to ~0.004 across the QCD axion mass range.
- Microlensing data provides a powerful tool for excluding or discovering the QCD axion if theoretical predictions improve.
Conclusions:
- The study provides the first observational limits on axion miniclusters, a potential component of dark matter.
- Microlensing surveys are sensitive probes of the axion minicluster scenario.
- Further dedicated analyses are required to confirm these initial constraints and their implications for axion cosmology.
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