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What are axions – real or not?

So, what are axions? I’ve noticed more articles lately about axions. Why all the fuss, eh?


The axion is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem [violation of the combined symmetries of charge conjugation and parity] in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter.

… the effective periodic strong CP-violating term, Θ-overline, appears as a Standard Model input – its value is not predicted by the theory, but must be measured. …

In 1977, Roberto Peccei and Helen Quinn postulated a more elegant solution to the strong CP problem, the Peccei–Quinn mechanism. The idea is to effectively promote Θ-overline to a field. This is accomplished by adding a new global symmetry (called a Peccei–Quinn symmetry) that becomes spontaneously broken. This results in a new particle, as shown independently by Frank Wilczek and Steven Weinberg, that fills the role of Θ-overline, naturally relaxing the CP-violation parameter to zero. Wilczek named this new hypothesized particle the “axion” after a brand of laundry detergent, while Weinberg called it “Higglet.” Weinberg later agreed to adopt Wilczek’s name for the particle. Because it has a non-zero mass [above 10^−11 times the electron mass; and with electric charge and spin = 0], the axion is a pseudo-Nambu–Goldstone boson.

So, how might axions be detected? Once again, an interplay of models and supercomputer simulations.

• > “Mystery particle may explain extreme X-rays shooting from the ‘Magnificent 7’ [neutron] stars” by Stephanie Pappas (January 22, 2021) – Never-before-seen particles called axions could be behind the mysterious X-rays.

… scientists have proposed a possible culprit: axions, theoretical particles that turn into light [electromagnetic radiation, in this case high-energy X-rays] particles when they are in the presence of a magnetic field.

[Lawrence Berkeley National Laboratory physicist] Safdi and his team found that axions might work a lot like neutrinos, another extremely light subatomic particle that has been shown to exist. Neutrinos are produced inside neutron stars when neutrons bump into one another; axions could be produced in the same way.

“We’re not claiming that we’ve made the discovery of the axion yet, but we’re saying that the extra X-ray photons can be explained by axions,” Raymond Co, a postdoctoral researcher at the University of Minnesota who collaborated on the study, said in the statement.

More to come … more re Wilczek (and his latest book) …

One thought on “What are axions – real or not?

  1. Re axions and dark matter, this article recaps the evidence for dark (invisible) matter. Includes a short video by Paul Sutter.

    • > “Scientists narrow down the ‘weight’ of dark matter trillions of trillions of times” by Tom Metcalfe (Feb 15, 2021)

    The research sharply narrows the potential mass of dark matter particles, from between an estimated 10^minus 24 electronvolts (eV) and 10^19 Gigaelectron volts (GeV) , to between 10^minus 3 eV and 10^7eV — a possible range of masses many trillions of trillions of times smaller than before.

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