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 $1e-6 \text{ to } 1e-3\, \mathrm{eV}$ 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.
What would settle it
Resonant-cavity, dielectric or plasma haloscopes scanning the 1e-6 to 1e-3 eV mass range at DFSZ sensitivity.
Status in the literature
Unverified 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).
Related problems
- Special case of What is dark matter made of?
- Special case of Does the QCD axion exist? · Axion making all dark matter is a sharper claim than axion existence
- More general than Axion-induced oscillating nucleon EDM at QCD-axion strength