Postdoctoral researcher: 'Our HYPER model illustrates that a phase transition can actually help make the dark matter more easily detectable'

Researchers from the University of Michigan and Johannes Gutenberg University of Mainz have proposed a new model for dark matter particles called HighlY Interactive ParticlE Relics or HYPER, a news release said.

The search for dark matter particles, such as WIMPS, has not yet led to success, so the research community is looking for alternative, lighter dark matter particles, the university said.

“There has not been a consistent dark matter model for the mass range that some planned experiments hope to access, said Gilly Elor, a postdoctoral researcher in theoretical physics at the Johannes Gutenberg University of Mainz in Germany. “However, our HYPER model illustrates that a phase transition can actually help make the dark matter more easily detectable.” 

The researchers’ HYPER model suggests that some time after the formation of dark matter in the early universe, the strength of its interaction with normal matter abruptly increased, which can explain the abundance of dark matter and make it potentially detectable today.

The challenge for a suitable model is that if dark matter interacts too strongly with normal matter, the amount formed in the early universe would be too small, contradicting astrophysical observations. However, if it is produced in just the right amount, the interaction would conversely be too weak to detect dark matter in present-day experiments, according to the news release.

The researchers’ central idea is that the interaction changes abruptly once, resulting in the right amount of dark matter and a large interaction that can potentially be detected. The interaction between dark matter and normal matter is usually mediated by a specific particle called a mediator, and the strength of the interaction depends on its mass. The mediator must first be heavy enough so that the correct amount of dark matter is formed and later light enough so that dark matter is detectable at all. The solution is a phase transition after the formation of dark matter, during which the mass of the mediator suddenly decreases, keeping the amount of dark matter constant and boosting the interaction in such a way that dark matter should be directly detectable.

The HYPER model of dark matter can cover almost the entire range that the new experiments make accessible, according to the researchers. The team first considered the maximum cross section of the mediator-mediated interaction with the protons and neutrons of an atomic nucleus to be consistent with astrophysical observations and certain particle-physics decays. The next step was to consider whether there was a model for dark matter that exhibited this interaction. They then calculated the amount of dark matter that exists in the universe and simulated the phase transition using their calculations.

The research team systematically considered and included many scenarios, such as whether the mediator would suddenly lead to the formation of new dark matter. The team ultimately concluded that the HYPER model works. The research was published in the journal, "Physical Review Letters."