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Quasiparticles known as magnons could help in detecting dark matter

Nearly 80% of the matter present in the cosmos has a form which is totally unknown to the physics of the present day. This is commonly known as dark matter. There have been several experiments all around the globe in an attempt to capture particle belonging to dark matter. Unfortunately, there have been no positive results. 

A group of scientists have come up with a new way of searching dark matter with the help of quasiparticles (not a real particle but something you can describe with math in that way) known as magnons. The theorists claim that these tiny so-called particles can bring out even lightweight particles of dark matter. 

Although dark matter cannot be detected directly, its evidence is visible with the help of telescopes. The first one came in the 1930s through the observation of galaxy clusters. They are one of the largest structures present in the universe. The galaxies present in these clusters are held together by the gravitational bonding which depends on the mass of the galaxies. Heavy galaxies mean stronger gravitational glues. However, it was detected that the galaxies were moving much faster than the limit set by the gravitational glue. This indicates that there must be something which is holding the clusters together and preventing them from ripping apart but not interacting or emitting light. 

Dark matter is present in every galaxy. The visible fraction in a galaxy comprising of stars, gas clouds, dust is just a tiny fraction compared to the zillions and zillions of dark matter particles. Particles of dark matter are present all around. However, they are not noticed because they do not interact with light or charged particles. The only way of observing dark matter is through the force of gravity. Each and every form of energy and matter in the universe, dark or not is influenced by gravitational forces. 

It is also possible that some particles of the dark matter interact with weak nuclear force, the one responsible for radioactive decays. In a very large detector, if a dark matter particle is heavy it knocks out the atomic nucleus of the element, via weak nuclear force and alters the mass of the detector. However, the lack of results is worrying, as the heaviest of the candidates have been ruled out. If these mysterious particles are too light, then the present setups cannot detect it.  

Therefore scientists have come up with a setup where the material is kept at absolute zero. Here, the electrons are in the same direction. However, if enough dark matter particles strike the material it would flip some of the spins. Each of those flipped spins also causes a little ripple in the energy of the material, and those wiggles can be viewed as a quasiparticle, not a true particle, but something you can describe with math in that way. These are called magnons. Thus it can detect a lightweight particle of a dark matter if it exists. 

Collage of six cluster collisions with dark matter maps

Scientists find a new candidate for dark matter along with ways to detect it

Two physicists from the University of California, Davis have got a new element for the position of dark matter and also a possible way for its detection. Their work was presented on June 6 at the Planck Conference which was held in Granada, Spain and it has also been submitted for publication in the near future.

It is estimated by researchers that dark matter comprises about a quarter of our universe, while the rest is composed of dark energy which is even more mysterious in the scientific world. Although it cannot be observed in a direct manner like normal matter, its presence can be detected through its gravity which helps in determining the shape of very distant galaxies and other such entities.

According to many researchers, dark matter is composed of an element which is yet to be identified. However the Weakly Interacting Massive Particle or WIMP has been considered as the most likely candidate for some time now. There is no clear cut definition of WIMP but it is broadly defined as a new type of elementary particle that interacts through gravity and other forces and is weaker than the weak nuclear force. Inspite of many efforts to detect it, WIMPs have not been observed in the experiments.

John Terning, a physics professor at UC Davis, who is also a coauthor of the paper said that it is not yet known for sure what is dark matter. Although WIMP was a candidate for a long time, it has been mostly ruled out. An alternative to the WIMP model is a kind of “dark electromagnetism” which includes elements such as “dark photons” and other types of particles.

In the paper, Terning along with fellow researcher Christopher Verhaaren provided a twist to the concept. It consists of a dark magnetic “monopole” interacting with dark photon. Monopole is a type of element which behaves like one end of magnet. Scientists hypothesize that dark monopoles interact with dark photons and dark electrons similar to the interaction of electrons and photons with monopoles.

The Aharonov-Bohm effect is the interference pattern in which electron when moving by a magnetic field is influenced by it while not passing through the field itself. Terning and Verhaaren remarked that a dark monopole can be detected because of the nature of shift of electrons while passing.

In a theoretical sense, the dark matter elements are passing around us all the time but to be detected in the model suggested by Terning and Verhaaren, they would have to be excited by sun. However the predicted phase shift is very small, smaller than value needed for detection of gravity waves.