Simple theory may explain mysterious dark matter

The reason dark matter - which makes up 85 per cent of all the matter in the universe - is invisible could be because it possesses a rare, donut-shaped type of electromagnetism instead of the more exotic forces that have been proposed, according to a new study.

Physicists from Vanderbilt University in US propose that dark matter may be made out of a type of basic particle called the Majorana fermion.
The particle's existence was predicted in the 1930's but has stubbornly resisted detection.

A number of physicists have suggested that dark matter is made from Majorana particles, but Professor Robert Scherrer and post-doctoral fellow Chiu Man Ho from Vanderbilt have performed detailed calculations that demonstrate that these particles are uniquely suited to possess a rare, donut-shaped type of electromagnetic field called an anapole.

This field gives them properties that differ from those of particles that possess the more common fields possessing two poles (north and south, positive and negative) and explains why they are so difficult to detect.

"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," said Scherrer.

"Further, the model makes very specific predictions about the rate at which it should show up in the vast dark matter detectors that are buried underground all over the world," Scherrer said.

"These predictions show that soon the existence of anapole dark matter should either be discovered or ruled out by these experiments," he said. Fermions are particles like the electron and quark, which are the building blocks of matter. Their existence was predicted by Paul Dirac in 1928.

"Although Majorana fermions are electrically neutral, fundamental symmetries of nature forbid them from acquiring any electromagnetic properties except the anapole," Ho said.

The anapole dark matter particles suggested by Ho and Scherrer would annihilate in the early universe just like other proposed dark matter particles, and the left-over particles from the process would form the dark matter we see today.