Physicists Propose New Way to Detect Dark Matter Particles

In a paper published in the journal Physical Review Letters, an international team of physicists proposes a new strategy for searching for hypothetical dark matter particles called axions using tunable plasmas.

Lawson et al propose a new instrument for searching dark matter axions using tunable plasmas. Image credit: Alexander Millar / Stockholm University.

Lawson et al propose a new instrument for searching dark matter axions using tunable plasmas. Image credit: Alexander Millar / Stockholm University.

Dark matter is the mysterious substance that makes up roughly a quarter of the Universe.

Theoretical physicists suspect that it is made of unseen particles that neither reflect nor absorb light, but are able to exert gravity.

Experiments around the world are attempting to detect and study such hypothetical particles. Among the leading candidates are the so-called axions.

“Originally introduced to explain why the Strong Force is the same backwards and forwards in time, axions would provide a natural explanation for dark matter,” said Stockholm University researcher Alexander Millar and his colleagues from Sweden, Germany, the United States, and China.

“Rather than discrete particles, axion dark matter would form a pervasive wave flowing throughout space.”

“Finding the axion is a bit like tuning a radio: you have to tune your antenna until you pick up the right frequency,” Dr. Millar added.

“Rather than music, experimentalists would be rewarded with hearing the dark matter that the Earth is traveling through.”

“Despite being well motivated, axions have been experimentally neglected during the three decades since they were named by Professor Frank Wilczek, Nobel laureate and co-author of this study.”

According to the team, inside a magnetic field, axions would generate a small electric field that could be used to drive oscillations in the plasma. These oscillations amplify the signal, leading to a better ‘axion radio.’

“Without the cold plasma, axions cannot efficiently convert into light,” said co-author Dr. Matthew Lawson, also from Stockholm University.

“The plasma plays a dual role, both creating an environment which allows for efficient conversion, and providing a resonant plasmon to collect the energy of the converted dark matter.”

To tune the ‘axion radio,’ the team proposes using something called a ‘wire metamaterial,’ a system of wires thinner than hair that can be moved to change the characteristic frequency of the plasma.

Inside a large, powerful magnet, a wire metamaterial turns into a very sensitive axion radio.

“Plasma haloscopes are one of the few ideas that could search for axions in this parameter space,” Dr. Millar said.

“The fact that the experimental community has latched onto this idea so quickly is very exciting and promising for building a full scale experiment.”


Matthew Lawson et al. 2019. Tunable Axion Plasma Haloscopes. Phys. Rev. Lett 123 (14); doi: 10.1103/PhysRevLett.123.141802

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