Discovery: Are gravitons the source of dark matter?

Massive gravitons may have formed a trillionth of a second after the Big Bang, with an excess large enough to form dark matter.

Dark matter, the mysterious substance that makes up most of the mass in the universe, may be made up of massive particles called gravitons, which first appeared in the first moments after the Big Bang. And these hypothetical particles could be the 'refugees' of the universe lurking in other dimensions, a new theory suggests.

The researchers' calculations suggest that these particles may have been produced in quantities just right to explain dark matter, which can only be 'seen' through its gravitational pull towards ordinary material. Study co-author Giacomo Cacciapaglia, a physicist at the University of Lyon, France, told Live Science: 'Graviton particles have mass produced by collisions of ordinary particles in the early universe. This process is thought to be too rare for large gravitons to be dark matter candidates.'

But in a new study published in February in the journal Physical Review Letters, Cacciapaglia, along with Korean University physicists Haiying Cai and Seung J. Lee, found that graviton particles were produced. enough in the early Universe, which explains the existence of the dark matter we are currently looking for in the universe.

Illustration for dark matter particles

Graviton has a small mass, only weakly interacting with ordinary matter through gravity

Research shows that gravitons, if they existed, would have a mass less than 1 megaelectronvolt (MeV), so the mass of an electron is not more than twice that of a graviton. This mass level is much lower than the scale at which the Higgs boson gives normal matter mass – key to the model having enough particles to play a role in creating all of the dark matter in the universe. pillar. (Note:, the lightest known particle, the neutrino, is less than 2 electronvolts, while a proton weighs about 940 MeV, according to the National Institute of Standards and Technology, USA).

The team found these putative gravitons while searching for evidence of additional dimensions, which some physicists suspect exist alongside the observable three-dimensional space and the second dimension. fourth, time.

According to the team's theory, as gravity propagates through additional dimensions, it materializes in our universe as massive gravitons.

Illustrating additional spatial dimensions according to string theory and other theories

But these particles would only interact weakly with ordinary matter, and only through gravity. This description is strangely similar to what we know about dark matter, matter that does not interact with light but has gravitational influence everywhere in the universe. For example, this gravitational effect is what prevents galaxies from moving away from each other.

Cacciapaglia said: 'The main advantage of mass gravitons as dark matter particles is that they only interact with gravity, so they can escape [human attempts to] detection of their presence.'

In contrast, other proposed dark matter candidates – such as weakly interacting mass particles, axions and neutrinos – could also be sensed by their very subtle interactions with forces and other schools.

The fact that gravitons have virtually no mass interact through gravity with other particles and forces in the universe, which offers another advantage.

Graivton formation in the early Universe

'Because their interactions are so weak, they decay so slowly that they remain stable throughout the lifetime of the universe,' says Cacciapaglia, 'for the same reason, they are produced slowly in the process. expansion of the universe and accumulated there to this day.'

Previously, physicists thought that gravitons were unlikely to be dark matter candidates because the processes that create them are extremely rare, which means that gravitons would be produced at a lower rate. more than other seeds.

But the team found that in the picosecond (trillionth of a second) after the Big Bang, more gravitons could be produced than previous theories suggested. The study found that this enhancement produced enough gravitons with mass to fully explain the amount of dark matter we detect in the universe.

Diagram of the creation of the universe from the Big Bang on the left – to the present.

Cacciapaglia said: 'This enhancement has come as a shock. We had to do many tests to make sure the result was correct, as it led to a paradigm shift in the way that we consider mass gravitons as potential candidates for matter. dark.'

The team's theory connects the results of physics research done at particle accelerators like the Large Hadron Collider with results from the physics of gravity. This leads scientists to hope that evidence of the existence of these potential dark matter particles could be found by 2035 when the Future Circle Accelerator at CERN (European Organization for Nuclear Research). ) goes into operation.

Cacciapaglia said: 'Probably the best picture we have [of the existence of dark matter] is at future high-precision particle accelerators.'