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Has dark energy finally been detected? University of Cambridge researchers interpret XENON1T experiment

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An experiment 1.5km below Italy’s Apennine Mountains designed to detect dark matter may instead have shown the presence of dark energy, University of Cambridge scientists suggest.

It is believed we can only see five per cent of the universe and everything else is ‘dark’. About 27 per cent is the invisible cosmic force holding galaxies together, known as dark matter, while 68 per cent is dark energy, which causes the universe to expand at an accelerated rate.

Dark energy could be produced in a region of the Sun called the tachocline, Cambridge researchers suggest
Dark energy could be produced in a region of the Sun called the tachocline, Cambridge researchers suggest

The XENON1T experiment - using pure liquid xenon shielded from cosmic rays in a cryostat - is designed to detect dark matter ‘hitting’ ordinary matter. A year ago, an unexpected signal, or excess, over the expected background, was found.

At the time, the most popular explanation for this were hypothetical, extremely light particles produced in the Sun, called axions, but the explanation has not stood up to observations.

Now researchers at Cambridge’s Kavli Institute for Cosmology say a physical model they have built using ‘chameleon screening’ shows dark energy particles produced in the Sun’s strong magnetic fields could explain the XENON1T excess.

“Our chameleon screening shuts down the production of dark energy particles in very dense objects, avoiding the problems faced by solar axions,” said Dr Sunny Vagnozzi from Cambridge’s Kavli Institute for Cosmology, the paper’s first author. “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.

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

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

But more studies are needed.

Co-author Dr Luca Visinelli, from Frascati National Laboratories in Italy, said: “We first need to know that this wasn’t simply a fluke. If XENON1T actually saw something, you’d expect to see a similar excess again in future experiments, but this time with a much stronger signal.”

If they are right, then upgrades that are coming to the XENON1T experiment, and similar experiments such as LUX-Zeplin and PandaX-xT, raise hopes that that dark energy could be detected directly within the next decade.

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