Professor John Terning and Dr. Christopher Verhaaren from the University of California, Davis, have a new candidate for dark matter — a dark monopole — and a possible way to detect it.
Dark matter is the mysterious substance that makes up roughly a quarter of the Universe.
Physicists suspect that dark matter is made of unseen particles that neither reflect nor absorb light, but are able to exert gravity.
“We still don’t know what dark matter is. The primary candidate for a long time was the WIMP, but it looks like that’s almost completely ruled out,” Professor Terning said.
An alternative to the WIMP model of dark matter calls for a form of ‘dark electromagnetism’ including ‘dark photons’ and other particles. Dark photons would have some weak coupling with ‘regular’ photons.
Professor Terning and Dr. Verhaaren add a twist to this idea: a dark magnetic monopole that would interact with the dark photon.
In the macroscopic world, magnets always have two poles, north and south. A monopole is a particle that acts like one end of a magnet.
“Dark monopoles would interact with dark photons and dark electrons in the same way that theory predicts electrons and photons interact with monopoles. And that implies a way to detect these dark particles,” they said.
In 1931, the English theoretical physicist Paul Dirac predicted that an electron moving in a circle near a monopole would pick up a change of phase in its wave function.
Because electrons exist as both particles and waves in quantum theory, the same electron could pass on either side of the monopole and as a result be slightly out of phase on the other side.
This interference pattern, called the Aharonov-Bohm effect, means that an electron passing around a magnetic field is influenced by it, even if it does not pass through the field itself.
“We could detect a dark monopole because of the way it shifts the phase of electrons as they pass by,” the scientists said.
“Theoretically, dark matter particles are streaming through us all the time. To be detectable in our model, the monopoles would have to be excited by the Sun. Then they would take about a month to reach Earth, traveling at about a thousandth of the speed of light,” Professor Terning said.
The team’s paper was posted on the arXiv.org website.
John Terning Christopher B. Verhaaren. 2019. Detecting Dark Matter with Aharonov-Bohm. arXiv: 1906.00014