Dark matter not so mysterious, say physicists

Dark matter makes up 85 percent of the matter of our Universe, but theories to explain it have usually been quite complicated. A new theory may hold a simple explanation for the unseen substance.

Dark matter, according to new research, may be composed of particles called Majorana fermions. These particles, first proposed in the 1930's but never detected, might have unusual doughnut-shaped magnetic fields known as anapoles. Although these theoretical particles have been previously proposed as an explanation for dark matter, the new calculations show that these particles likely possess such anapoles, which could explain how they have avoided detection for so long.

Robert Scherrer and Chiu Man Ho from Vanderbilt University were able to show that these fermions, which do not carry an electric charge, could only possess anapole magnetic fields, not more familiar forms. Such anapoles, which have observed in some atomic nuclei, are characterized by the fact that their magnetic fields do not interact with other particles unless they are in motion. The faster Majorana fermions move, the more they interact. Other types of fermions include quarks and electrons.

"There are a great many different theories about the nature of dark matter. What I like about this theory is its simplicity, uniqueness and the fact that it can be tested," Scherrer said.

Dark matter was first proposed in the 1930's, when it became apparent that stars were rotating around galaxies far faster than the amount of visible matter in the galaxy would predict. Unseen matter forming a halo around galaxies became the defining theory to explain the phenomenon.

"Most models for dark matter assume that it interacts through exotic forces that we do not encounter in everyday life. Anapole dark matter makes use of ordinary electromagnetism that you learned about in school - the same force that makes magnets stick to your refrigerator or makes a balloon rubbed on your hair stick to the ceiling," Scherrer said.

Because faster-moving Majorana fermions affect the world around them to a greater degree that slower-moving particles would explain why these fermions are so hard to find today. Active in the time right after the Big Bang, they interacted less with their environment as the Universe cooled and slowed its expansion.

Results of the study were published in the journal Physics Letters B on May 24.  

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