Scientists from Durham University and Kings College London have presented a
theoretical review in a new study strongly supporting the search for axion
dark matter.
The identity of dark matter, which makes up 85% of the matter in the
universe, is one of the big unanswered questions in particle physics.
Scientists know of its existence because of its gravitational pull effects
on stars and galaxies but what kind of particle it is, still remains a
mystery.
The researchers analyzed how axions can be described mathematically and
presented how they relate to the fundamental symmetries of the Standard
Model of particle physics.
The axion explains why the strong interaction—the force that binds together
quarks in protons and neutrons—obeys time reversal symmetry. This means
that, at the subatomic level, processes caused by the strong interaction
would look the same if the direction of time was reversed.
Why the strong interaction obeys time reversal symmetry is still unknown.
The axion is a popular solution to this mystery.
Axion dark matter behave more like a field covering the universe than like
individual particles. In the early universe, the value of the axion field
begins to oscillate back and forth. The energy stored in these oscillations
is axion dark matter.
It is known that dark matter of any kind can only interact very weakly with
light, or else it would have been seen by scientists already. Axion dark
matter interacts with light very weakly, but by looking closely at telescope
observations the researchers might be able to see signs of this interaction.
For example, a photon (a particle of light) traveling through a magnetic
field would have a small probability of turning into an axion. This process
would cause unusual features in telescope observations of galaxies shining
through magnetic fields.
The full analysis of the study was published in Science Advances. A
companion review paper—"Axion Dark Matter: How to see it?" by Yannis
Semertzidis and SungWoo Youn—shows how the axion could be detected in the
lab soon.
Study co-author, Dr. Francesca Chadha-Day, said: "It is a very exciting time
to be an axion physicist. Nobody yet knows the identity of dark matter. By
searching for different possibilities, such as the axion, we hope to one day
solve this mystery."
The researchers hope that this review will increase interest and
understanding of axion physics within the broader community of physicists
and scientists.
References:
Francesca Chadha-Day et al, Axion dark matter: What is it and why now?,
Science Advances (2022).
DOI: 10.1126/sciadv.abj3618.
Yannis K. Semertzidis et al, Axion dark matter: How to see it?, Science
Advances (2022).
DOI: 10.1126/sciadv.abm9928.
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Physics