Two experiments hunting for a whisper of a particle that prevents whole galaxies from flying apart recently published some contradictory results. One came up empty handed, while the other gives us every reason to keep on searching.
Dark bosons are dark matter candidates based on force-carrying particles that don't really pack much force.
Unlike the bosons we're more familiar with, such as the photons that bind molecules and the gluons that hold atomic nuclei together, an exchange of dark bosons would barely affect their immediate surroundings.
If they existed, on the other hand, their collective energy could be responsible for making up dark matter - the missing mass that provides the extra gravity needed to keep our Universe of stars in their familiar formations.
Unfortunately, the presence of such bosons would be about as detectable as a murmur in a storm. For a physicist, however, a murmur might be enough to still be noticeable given the right kind of experiment.
The two studies – one led by researchers from the Massachusetts Institute of Technology (MIT), the other by Aarhus University in Denmark – looked for subtle differences in the positioning of an electron in an isotope as it jumped between energy levels. If it swayed, this could be a telltale sign of a dark boson's nudge.
That boson, in theory, would come from an interaction between the orbiting electron and the quarks making up neutrons in the atom's nucleus.
The MIT-led team used a handful of ytterbium isotopes for their experiment, while calcium was the element of choice for the Aarhus University-led group.
Both experiments lined up their data on a type of plot specific to measuring these kinds of movements in isotopes. While the calcium-based experiment appeared as predicted, the ytterbium plot was off, with a statistically significant deviation in the plot's linearity.
This isn't a cause for celebration of any sort. For one thing, while a boson could explain the numbers, so could a difference in the way they carry out calculations, a type of correction called a quadratic field shift.
Exactly why one experiment might have found something odd and the other found nothing at all is also in need of an explanation.
As always, we need more data. A lot more. But figuring out exactly what makes up more than a quarter of the Universe is one of the biggest questions in science, so any potential leads are going to be pursued with excitement.
Adding new kinds of force-carrying particles to the Standard Model isn't exactly ruled out by anything in physics, but finding one would be a huge deal.
Last year physicists were excited by particles moving away at weird angles, hinting at a hitherto unknown force at work.
Similarly, the number of electrons recoiling in the XENON1T dark matter setup got tongues wagging early this year, inviting speculation over a hypothetical dark matter candidate called an axion.
As interesting as these results are, we've had our hearts broken before. In 2016, a type of dark matter candidate called a Madala Boson was rumoured to have been spotted among data collected by the Large Hadron Collider in its search for the Higgs particle.
This particle could be thought of as a kind of dark version of the Higgs boson, lending dark matter its strength without making itself clear in any other way.
CERN threw cold water over that bit of gossip, sad to say. Which doesn't mean such a particle doesn't exist, or that signs aren't tempting – just that we can't confirm it with any real degree of confidence.
Bigger colliders, more sensitive equipment, and clever new ways to search for subtle nudges and whispers of virtually non-existent particles might one day get us the answers we need.
Dark matter sure isn't going to make it easy.
This research was published in Physical Review Letters, here and here.
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