Is dark matter the QCD axion?
In plain words
The axion is a very light hypothetical particle invented to explain why the strong force does not distinguish past from future in a certain way, and it could also be dark matter. Experiments try to convert axions into microwave photons inside strong magnets.
Precise statement
Does a QCD axion with mass $m_a$ in roughly $10^{-6} \text{ to } 10^{-3}\, \mathrm{eV}$ and photon coupling $g_a-\gamma$ on the KSVZ or DFSZ model bands constitute $\Omega_c$? An answer is a haloscope or helioscope detection at a fixed frequency $\nu = m_a c^2 / h$ with the predicted coupling, or exclusion of the DFSZ band over the mass range favored by post-inflationary production.
What would settle it
Resonant-cavity, dielectric or plasma haloscopes scanning the $10^{-6}$ to $10^{-3}$ eV mass range at DFSZ sensitivity.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
As of 2025 haloscopes such as ADMX reach DFSZ sensitivity only over narrow mass intervals near a few micro-eV (moderate confidence on the exact range).
Parent problems
- Special case of What is dark matter made of? · open · from revision 1
- Special case of Does the QCD axion exist? · open · from revision 1 Axion making all dark matter is a sharper claim than axion existence The parent was revised since revision 1: it now states another question.
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