Have we detected dark energy? Scientists say it’s a possibility

A new study, conducted by researchers at the University of Cambridge and published in the journal Physical examination Dsuggests that some unexplained results from the XENON1T experiment in Italy may have been caused by dark energy, and not by the dark matter that the experiment was designed to detect.

They built a physical model to help explain the findings, which could come from dark energy particles produced in a region of the Sun with strong magnetic fields, although future experiments are needed to confirm this explanation. The researchers say their study could be an important step towards the direct detection of dark energy.

Everything our eyes can see in the sky and in our everyday world, from tiny moons to massive galaxies, from ants to blue whales, is less than five percent of the universe. The rest is dark. About 27% is dark matter, the invisible force that holds galaxies and the cosmic web together, while 68% is dark energy, which causes the universe to expand at an accelerated rate.

“Although the two components are invisible, we know a lot more about dark matter, since its existence was suggested as early as the 1920s, while dark energy was not discovered until 1998,” said the Dr Sunny Vagnozzi of the Kavli Institute for Cosmology in Cambridge, the first author of the article. “Large-scale experiments like XENON1T have been designed to detect dark matter directly, looking for signs of dark matter” hitting “ordinary matter, but dark energy is even more elusive.”

To detect dark energy, scientists typically look for gravitational interactions: the way gravity drives objects. And on larger scales, the gravitational effect of dark energy is repulsive, pushing things apart and accelerating the expansion of the Universe.

About a year ago, the XENON1T experiment reported an unexpected signal, or excess, over the expected background noise. “These types of excess are often fluids, but every now and then they can also lead to fundamental discoveries,” said Dr Luca Visinelli, researcher at the Frascati National Laboratories in Italy, co-author of the study. “We explored a model in which this signal could be attributable to dark energy, rather than the dark matter that the experiment was originally designed to detect.”

At the time, the most popular explanation for the excess was axions – hypothetical extremely light particles – produced in the Sun. However, this explanation does not stand up to observations, since the quantity of axions that would be necessary to explain the XENON1T signal would drastically modify the evolution of stars much heavier than the Sun, in contradiction with what we observe.

We are far from fully understanding what dark energy is, but most physical models of dark energy would lead to the existence of a so-called fifth force. There are four fundamental forces in the universe, and anything that cannot be explained by one of these forces is sometimes referred to as the result of an unknown fifth force.

However, we do know that Einstein’s theory of gravity works extremely well in the local universe. Therefore, any fifth force associated with dark energy is undesirable and must be “hidden” or “masked” when it comes to small scales, and can only work at larger scales where the theory of gravity Einstein does not explain the acceleration of the Universe. To mask the fifth force, many models of dark energy are equipped with so-called filtering mechanisms, which dynamically mask the fifth force.

Vagnozzi and his co-authors built a physical model, which used a type of filtering mechanism known as chameleon filtering, to show that dark energy particles produced in the Sun’s strong magnetic fields could explain the excess of XENON1T.

“Our chameleon screening stops the production of dark energy particles in very dense objects, avoiding the problems encountered by solar axions,” said Vagnozzi. “It also allows us to decouple what is happening in the very dense local Universe from what is happening at larger scales, where the density is extremely low.”

The researchers used their model to show what would happen in the detector if dark energy was produced in a particular region of the Sun, called the tachocline, where magnetic fields are particularly strong.

“It was really surprising that this excess could in principle be caused by dark energy rather than dark matter,” Vagnozzi said. “When things fit together like that, it’s really special.”

Their calculations suggest that experiments like XENON1T, which are designed to detect dark matter, could also be used to detect dark energy. However, the initial excess has yet to be convincingly confirmed. “First we have to know that it was not just a fluke,” Visinelli said. “If XENON1T actually saw anything, you would expect to see a similar excess again in future experiments, but this time with a much stronger signal.”

If the excess was the result of dark energy, upcoming upgrades to the XENON1T experiment, as well as experiments pursuing similar goals such as LUX-Zeplin and PandaX-xT, mean it might be possible. to directly detect dark energy over the next decade.