Axions: A Second GOD Particle?
Dark matter makes up 1/3 of our current understanding of the Universe, yet we have no idea what it is.
Why is that?
One of the most significant reasons for this is because Dark Matter is highly undetectable. It doesn’t interact with light, which means that light cannot bounce off of it, rendering it undetectable (mostly). This is why many scientists have set up experiments based on renowned theories to search for probable Dark Matter candidates.
One of these prominent theories arises from a possible solution of a few fundamental problems, especially the Strong CP Problem. This problem stems from a concept of Symmetry. Symmetries essentially describe a system where any transformations done to the system, will not change the system itself. The Strong CP Problem describes in theory how the Strong Nuclear Force, which is mediated by gluons, shouldn’t necessarily obey Charge-Parity Symmetry (a transformation containing the changing of a charge and the spacial location). But this isn’t the case, since experiments done by scientists have not resulted in any violations of this Symmetry.
In theory, if CP Symmetry is not conserved by the Strong Nuclear Force, then neutrons should be exerting an electric field. Even though neutrons have a neutral charge, since they are made up of quarks which do have charges, it should interact with the electric field. The only catch is that we haven’t recorded this in any experiment done till date.
This Lagrangian describes motion arising from Quantum Chromodynamics and is essential in solving the Strong CP Problem.
This equation has a problem because the terms coupled with theta violates the CP Symmetry. There are a few solutions to this, one being giving theta the value 0. Theta is supposed to be a phase shift of the infinite vacuum states, but keeping the value as 0 will not tell us exactly if this is the correct solution. This is why physicists kept searching for another possible solution, which was eventually put forth by Physicists, Roberto Peccei and Helen Quinn. They suggested that theta could be set as a field since, the field will always try to go to the lowest energy state, resulting in a value of 0 and cancelling out the terms that are multiplied by it.
But what is so important about this?
Well, we have to remember that particles are excitations of fields, which means that if this proposed solution works, then the new field should produce a particle. This particle, scientists believed, should be known as the Axion.
The Axion is not only special because it could solve the Strong CP Problem, but it can also serve as a candidate for dark matter. This particle would not interact strongly with all but one of the fundamental forces, through the electromagnetic field. This would fit the present situation as Dark Matter seems undetectable, but experiments such as the ADMX in UW could find the axion through experimenting with their strong magnetic fields that could change the axions into microwave photons.
This theory that axions can transform into photons and change back into axions could give another reason why it is been so difficult to detect Dark Matter. Since they can turn into photons and back into axions, it could make them undetectable for periods of time.
The Axion has been sought out by different research groups like the ADMX, ALPS, and CERN. They have not been detected yet, but this might be because of its low interactivity with well anything, but specifically with the electromagnetic field since some of these experiments are using strong electromagnetic fields to search for them.
Axions could also explain Dark Matter’s mysterious phenomenon of holding galaxies together. This shouldn’t be possible since galaxies spin and all the matter should fly apart, but since the axions have these similar properties, we could be looking to witness one of the most important discoveries of all time.
Although this particle hasn’t been found yet, it could solve many problems such as the Strong CP Problem, Dark Matter, and another important one: why there is more matter than anti-matter.
There is a theory that the field that produces axions represented by theta oscillated. This would create axions, and their interactions with the strong and weak nuclear forces would create more one matter than anti-matter. This would make the rest of the pairs of matter anti-matter collide and pop out of existence.
Axions seem to be able to solve the most important problems in our Universe, and there are many experiments that are searching for this particle. Hopefully we find good results!
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