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Title: Is dark matter the QCD axion?
Plain: 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: Does a QCD axion with mass $m_a$ in roughly $1e-6 \text{ to } 1e-3\, \mathrm{eV}$ 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.
Settled by: Resonant-cavity, dielectric or plasma haloscopes scanning the 1e-6 to 1e-3 eV mass range at DFSZ sensitivity.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: 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).
Posed since: 1983