The dark energy, the mysterious force that causes the universe to accelerate, may have been responsible for unexpected results of the XENON1T experiment, far below the Apennine mountains of Italy.
A new study, led by researchers at Cambridge University and published in the journal Physical check D, suggests that some unexplained results of the XENON1T experiment in Italy may have been caused by dark energy, not by the dark matter the experiment was designed to detect.
“It was surprising that this excess in principle could have been caused by dark energy rather than dark matter. When things click together, it’s very special. ” Sunny Vagnozzi
They built a physical model to help explain the results, which may have originated from dark energy particles produced in a region of the Sun with strong magnetic fields, although experiments will have to be done in the future to confirm this explanation. Researchers say their study could be an important step toward direct detection of dark energy.
Everything our eyes can see in the sky and in our everyday world (from small moons to massive galaxies, from ants to blue whales) makes up 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 network together), while 68% is dark energy, causing the universe to expand at an accelerated rate.
“While both components are invisible, we know much more about dark matter, as its existence was suggested as early as the 1920s, while dark energy was not discovered until 1998,” he said. Dr. Sunny Vagnozzi of the Kavli Institute of Cosmology in Cambridge, the first author of the paper. “Large-scale experiments like XENON1T have been designed to directly detect dark matter, looking for signs of dark matter that ‘hit’ ordinary matter, but dark energy is even harder to evade.”
To detect dark energy, scientists often look for gravitational interactions: the way gravity drags objects. And on larger scales, the gravitational effect of dark energy is repulsive, moving things away from each other and accelerating the expansion of the Universe.
About a year ago, the XENON1T experiment reported an unexpected signal, or an excess, on the expected background. “Such excesses are usually exits, but from time to time they can also lead to fundamental discoveries,” said Dr. Luca Visinelli, a researcher at 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 that time, the most popular explanation for the excess was the axions (extremely light hypothetical particles) produced in the Sun. However, this explanation does not withstand the observations, as the amount of action required to explain the XENON1T signal would drastically alter the evolution of stars much heavier than the Sun, in conflict 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 the so-called fifth force. There are four fundamental forces in the universe, and anything that one of these forces cannot explain is sometimes known as the result of a fifth unknown force.
However, we know that Einstein’s theory of gravity works very well in the local universe. Therefore, any fifth force associated with dark energy is not desirable and should be “hidden” or “filtered” when it comes to small scales and can only operate on larger scales where Einstein’s theory of gravity it does not explain the acceleration of the Universe. To hide the fifth force, many dark energy models are equipped with so-called detection mechanisms, which dynamically hide the fifth force.
Vagnozzi and his co-authors constructed a physical model, which used a type of detection mechanism known as chameleon detection, to show that dark energy particles produced in the Sun’s strong magnetic fields could explain the excess of XENON1T.
“Our chameleon examination stops the production of dark energy particles in very dense objects, avoiding the problems faced by solar axions,” Vagnozzi said. “It also allows us to separate what happens in the very dense local universe from what happens on the larger scales, where the density is extremely low.”
The researchers used their model to show what would happen to the detector if dark energy was produced in a particular region of the Sun, called the tachocline, where the magnetic fields are particularly strong.
“It was really amazing that this excess in principle could have been caused by dark energy rather than dark matter,” Vagnozzi said. “When things click together like that, it’s really special.”
His calculations suggest that experiments like XENON1T, designed to detect dark matter, could also be used to detect dark energy. However, the original excess has yet to be convincingly confirmed. “We first need to know that this was not just a coincidence,” Visinelli said. “If XENON1T really saw anything, you’ll 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, future updates to the XENON1T experiment, as well as experiments pursuing similar goals, such as LUX-Zeplin and PandaX-xT, mean that energy could be detected directly. dark over the next decade.
Reference: “Direct Detection of Dark Energy: XENON1T Excess and Future Prospects” by Sunny Vagnozzi, Luca Visinelli, Philippe Brax, Anne-Christine Davis and Jeremy Sakstein, September 15, 2021, Physical check D.
DOI: 10.1103 / PhysRevD.104.063023