axion

History

In 1977, theorists Roberto Peccei and Helen Quinn proposed this particle to fix a mismatch in the theory of the force that glues protons together. Later, Frank Wilczek named it the axion after a cleaning powder that 'cleans up' the theory of the problem.

How it works

Axions, like ghosts, pass through walls and our bodies, almost without noticing ordinary matter. But if you place them in a powerful magnetic field, some of them can turn into tiny flashes of light (photons), which scientists are trying to catch with sensitive instruments.

History

In 1977, theorists Roberto Peccei and Helen Quinn proposed this particle to fix a mismatch in the theory of the force that glues protons together. Later, Frank Wilczek named it the axion after a cleaning powder that 'cleans up' the theory of the problem.

How it works

Axions, like ghosts, pass through walls and our bodies, almost without noticing ordinary matter. But if you place them in a powerful magnetic field, some of them can turn into tiny flashes of light (photons), which scientists are trying to catch with sensitive instruments.

History

The Peccei-Quinn mechanism was published in 1977, and soon Frank Wilczek and Steven Weinberg independently predicted a light boson. Wilczek named it the axion, by analogy with a cleaning agent that 'cleans up' QCD from the strong CP problem. In the 1980s, the first experiments were proposed, including a 'magnetic sequester.' In the 21st century, axion searches have become one of the main directions of particle physics, intertwined with astrophysics and cosmology.

How it works

The axion field a(x) interacts with electromagnetism through the term (g_{aγγ}/4) a F_{μν} ilde{F}^{μν} in the Lagrangian. In an external magnetic field, this leads to the conversion of axions into photons. Cosmologically, axions are born at the spontaneous breaking of symmetry, and their field is frozen until the moment when the mass becomes comparable to the Hubble rate; then it begins to oscillate, behaving as cold dark matter. For detection, resonance in microwave cavities is used (frequency is related to the axion mass) with sensitivity g_{aγγ} ~ 10^{-16} GeV^{-1}.

Open problems & fun facts

The mass range of the axion is not experimentally constrained and spans several orders of magnitude; The existence of axion-like particles not related to the CP problem complicates the search; Cosmological constraints from observations of the cosmic microwave background require fine-tuning of the initial conditions of the field

💡 Around neutron stars, axion clouds could form, generating a radio signal that telescopes are currently trying to catch.