Axions: Strange particles may explain dark matter

Axions are hypothetical particles that have been postulated to exist in order to solve the strong CP problem in particle physics. The strong CP problem is a theoretical issue that arises from the Standard Model of particle physics. The Standard Model predicts a property known as CP violation. CP violation refers to a subtle difference in the behavior of particles and their antiparticles. Strangely, the amount of CP violation predicted by the Standard Model is much larger than what is observed in experiments, leading to the strong CP problem.

CP Violation

CP violation is a fundamental property of the strong force, which is responsible for holding the nucleus of an atom together. The strong force is one of the four fundamental forces of nature, along with the weak force, the electromagnetic force, and gravity. The strong force is mediated by particles called gluons, which are also affected by CP violation. However, the Standard Model predicts a CP violation much larger than what is observed in experiments. Axions could explain the difference.

Axions to the Rescue?

Axions were first proposed by Roberto Peccei and Helen Quinn in 1977 as a way to explain the smallness of CP violation. Physicists predicted they would weakly interact with other matter, which makes them difficult to detect. They are also predicted to be very light, much smaller than the tiny mass of an electron.

One of the most promising experiments to search for axions is the Axion Dark Matter eXperiment (ADMX), which is located at the University of Washington. ADMX uses a large superconducting magnet to search for the particles. They might be present in the dark matter that supposedly permeates the universe.

Dark matter is a mysterious substance that might make up matter in the universe, but its existence has not been detected. Axions are one of the leading candidates for dark matter, making ADMX an important dark matter experiment.

Scientists have conducted another experiment to search for axions is the CERN Axion Solar Telescope (CAST), located in Geneva, Switzerland. CAST tries to use a large magnet to convert axions that might be produced by the Sun into detectable light. Neither of these experiments has conclusively detected axions, but they constrain the properties that these elusive particles could have.

No Evidence for Axions Yet

Right now, physicists have not confirmed their existence. But, in the words of Frank Wilczek, a Nobel laureate in physics and one of the pioneers of axion research, “Axions are a very elegant solution to the strong CP problem. They are also a very promising candidate for dark matter. Although we have not yet detected them, the hunt for axions is still ongoing, and I am optimistic that we will find them eventually.”

Ultimately, a discovery of axions would be major breakthrough in our understanding of fundamental particles and could also shed light on the nature of dark matter.