Phase transition in the early universe changes the strength of the interaction between dark and normal matter.
Dark matter remains one of the greatest mysteries of modern physics. It is clear that it must exist, because without dark matter, for example, the movement of galaxies cannot be explained. But it has never been possible to detect dark matter in an experiment.
Currently, there are many proposals for new experiments: they aim to detect dark matter directly via its scattering from the constituents of the atomic nuclei of a detection medium, i.e. protons and neutrons.
A team of researchers — Robert McGehee and Aaron Pierce of the University of Michigan and Gilly Elor of the Johannes Gutenberg University of Mainz in Germany — have now proposed a new dark matter candidate: HYPER, or “Highly Interactive ParticlE Relics.”
In the HYPER model, some time after the formation of dark matter in the early universe, the strength of its interaction with normal matter abruptly increases, which on the one hand makes it potentially detectable and at the same time explains the abundance of dark matter. matter.
The new diversity in the dark matter sector
Because the search for heavy dark matter particles, or so-called WIMPS, has not yet led to success, the research community is looking for alternative dark matter particles, especially lighter ones. At the same time, you generically expect phase transitions in the dark sector — after all, there are several of them in the visible sector, the researchers say. But previous studies tend to neglect them.
“There has been no consistent model of dark matter for the mass range that some planned experiments hope to achieve. However, our HYPER model illustrates that a phase transition can actually help make the dark matter more easily detectable,” said Elor, a postdoctoral researcher. in theoretical physics at JGU.
The challenge for a suitable model: If dark matter interacts too strongly with normal matter, the (accurately known) amount formed in the early universe would be too small, contradicting astrophysical observations. However, if produced in just the right amount, the interaction would conversely be too weak to detect dark matter in current experiments.
“Our central idea, which underpins the HYPER model, is that the interaction changes abruptly once, so we can have the best of both worlds: the right amount of dark matter and a large interaction so that we can detect it,” said McGehee.
And this is how the researchers envision it: In particle physics, an interaction is usually mediated by a specific particle, a so-called mediator – and so is the interaction of dark matter with normal matter. Both the formation of dark matter and its detection function through this mediator, where the strength of the interaction depends on the mass: the larger the mass, the weaker the interaction.
The mediator must first be heavy enough so that the right amount of dark matter is formed and later light enough that dark matter is detectable at all. The solution: There was a phase transition after the formation of dark matter, in which the mass of the mediator suddenly decreased.
“This way, on the one hand, the amount of dark matter is kept constant, and on the other hand, the interaction is stimulated or amplified in such a way that dark matter should be immediately detectable,” said Pierce.
The new model covers almost the entire parameter range of planned experiments
“The HYPER model of dark matter can cover almost the entire range that the new experiments make accessible,” said Elor.
Specifically, the research 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 astrological observations and certain particle physical decays. The next step was to see if there was a dark matter model that showed this interaction.
“And this is where we came up with the idea of the phase transition,” McGehee said. “We then calculated the amount of dark matter in the universe and then simulated the phase transition using our calculations.”
There are many constraints to consider, such as a constant amount of dark matter.
“Here we have to systematically consider and include a lot of scenarios, for example by asking whether it is really certain that our mediator will not suddenly lead to the formation of new dark matter, which of course should not be,” said Elor. . “But in the end we were convinced that our HYPER model works.”
The research will be published in the journal Physical assessment letters.
Reference: “Maximizing Instant Detection with Highly Interactive Particle Relic Dark Matter” By Gilly Elor, Robert McGehee, and Aaron Pierce, January 20, 2023, Physical assessment letters.