Doughnut-shaped electromagnetic fields demystify dark matter

A pair of physicists say their simple theory may explain dark matter – the mysterious, invisible form of matter that makes up 85% of the universe.

Professor Robert Scherrer and post-doctoral fellow Chiu Man Ho from Vanderbilt University have performed calculations that suggest dark matter could be made out of particles called Majorana fermions that possess a rare, doughnut-shaped electromagnetic field called an anapole.

“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.

The Majorana ferminon’s existence was predicted in the 1930s, but it has stubbornly resisted detection.

A number of physicists have suggested the dark matter is made from Majorana particles, but Scherrer and Ho are the first to provde detailed calculations which demonstrate that Majorana particles are uniquely suited to possess a rare, doughnut-shaped type of electromagnetic field called an anapole. This field gives them different properties and explains why they are so hard to detect.

The anapole dark matter particles suggested by the team 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.

Particles with familiar electrical and magnetic dipoles interact with electromagnetic fields even when stationary, but particles with anapole fields do not. In order to interact, Majorna particles must be moving and the faster they move, the stronger the interaction. Because of this, anapole particles would have been much more interactive during the early days of the universe and would have become less and less interactive as the universe expanded and cooled.

However, the pair say their theory can be tested and the existence of anapole dark matter should either be discovered or ruled out by results from current underground dark matter detectors world-wide.

“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,” said Scherrer.

The team’s research is published in Physics Letters B.