More is unknown than is known. It turns out that roughly 68% of the Universe is dark energy.
A new study reports that some unexplained results from the XENON1T experiment in Italy may have been caused by dark energy and not the dark matter the experiment was designed to detect.
According to scientists, dark energy particles are produced in a region of the Sun with strong magnetic fields. Scientists from the University of Cambridge have constructed a physical model to help explain the results. The study is an essential step toward the direct detection of dark energy.
Dr. Sunny Vagnozzi from Cambridge’s Kavli Institute for Cosmology, the paper’s first author, said, “Despite both components being invisible, we know a lot more about the dark matter since its existence was suggested as early as the 1920s, while dark energy wasn’t discovered until 1998. Large-scale experiments like XENON1T have been designed to directly detect dark matter by searching for signs of dark matter ‘hitting’ ordinary matter, but dark energy is even more elusive.”
The XENON1T experiment reported an unexpected signal, or excess, over the expected background.
Dr. Luca Visinelli, a researcher at Frascati National Laboratories in Italy, a co-author of the study, said, “These sorts of excesses are often flukes, but once in a while, they can also lead to fundamental discoveries. We explored a model in which this signal could be attributable to dark energy, rather than the dark matter the experiment was originally devised 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 number of axions that would be required to explain the XENON1T signal would drastically alter the evolution of stars much heavier than the Sun, in conflict with what we observe.”
The model that scientists developed used a type of screening mechanism known as chameleon screening. The model showed that ark energy particles produced in the Sun’s intense magnetic fields could explain the XENON1T excess.
Vagnozzi said, “Our chameleon screening shuts down the production of dark energy particles in very dense objects, avoiding the problems faced by solar axions. It also allows us to decouple what happens in the local very dense Universe from what happens on the largest scales, where the density is extremely low.”
Using the model, scientists also shown what would happen in the detector if the dark energy was produced in a particular region of the Sun, called the tachocline, where the magnetic fields are powerful.
The calculation also suggests that experiments like XENON1T, designed to detect dark matter, could also be used to detect dark energy. However, the original excess still needs to be convincingly confirmed.
Vagnozzi said, “It was astonishing that this excess could in principle have been caused by dark energy rather than dark matter. When things click together like that, it’s really special.”
Visinelli said, “We first need to know that this wasn’t simply a fluke. If XENON1T saw something, you’d expect to see a similar excess again in future experiments, but this time with a much stronger signal.”
- Sunny Vagnozzi et al., Direct detection of dark energy: The XENON1T excess and prospects, Physical Review D (2021). DOI: 10.1103/PhysRevD.104.063023