Dark Matter: Can Simple Anapole theory explain it?

This is a comparison of an anapole field with common electric and magnetic dipoles. The anapole field, top, is generated by a toroidal electrical current. 

As a result, the field is confined within the torus, instead of spreading out like the fields generated by conventional electric and magnetic dipoles. 

Credit: Michael Smeltzer, Vanderbilt University

Most of the matter in the universe may be made out of particles that possess an unusual, donut-shaped electromagnetic field called an anapole.

This proposal, which endows dark matter particles with a rare form of electromagnetism, has been strengthened by a detailed analysis performed by a pair of theoretical physicists at Vanderbilt University: Professor Robert Scherrer and post-doctoral fellow Chiu Man Ho.

An article about the research was published online last month by the journal Physics Letters B.

"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.

Robert Scherrer

In the article, titled "Anapole Dark Matter," the physicists propose that dark matter, an invisible form of matter that makes up 85 percent of the all the matter in the universe, 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 Scherrer and Ho have performed detailed calculations that demonstrate that these particles are uniquely suited to possess a rare, doughnut-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. These predictions show that soon the existence of anapole dark matter should either be discovered or ruled out by these experiments."

More information: Anapole dark matter. Physics Letters B, 2013; 722 (4-5): 341 DOI: 10.1016/j.physletb.2013.04.039 ( adsabs.harvard.edu/abs/2013PhLB..722..341)