(ORDO NEWS) — Dark matter, the elusive stuff that makes up most of the mass of the universe, may be made up of massive particles called gravitons that appeared in the first moment after the Big Bang.
And these hypothetical particles could be cosmic refugees from extra dimensions, a new theory suggests.
The researchers’ calculations hint that these particles could have been created in sufficient quantities to explain dark matter, which can only be “seen” through its gravitational pull on ordinary matter.
“Massive gravitons are formed as a result of collisions of ordinary particles in the early Universe.
This process was thought to be too rare for massive gravitons to be candidates for dark matter,” study co-author Giacomo Cacchapaglia, a physicist at the University of Lyon in France, told Live Science.
But in a new study published in February in the journal Physical Review Letters, Cacchapallia, along with Korea University physicists Hayin Kaem and Seung J. Lee, found that enough of these gravitons were created in the early universe to explain all the dark matter we are now detecting. in the Universe.
Gravitons, if they exist, would have a mass of less than 1 megaelectronvolt (MeV), that is, no more than twice the mass of an electron, the study says.
This mass level is far below the scale at which the Higgs boson creates mass for ordinary matter – which is key to a model that can create enough of them to explain all the dark matter in the universe.
(For comparison, the lightest particle known, the neutrino, weighs less than 2 electron volts, and the mass of a proton is about 940 MeV, according to the National Institute of Standards and Technology.)
The team discovered these hypothetical gravitons while searching for evidence of extra dimensions, which some physicists believe exist alongside the observed three dimensions of space and the fourth dimension, time.
According to the team’s theory, when gravity propagates through extra dimensions, it materializes in our universe in the form of massive gravitons.
But these particles will weakly interact with ordinary matter and only through the force of gravity.
This description is eerily similar to what we know about dark matter, which does not interact with light, but exerts a gravitational influence felt throughout the universe. This gravitational influence, for example, does not allow galaxies to scatter in different directions.
“The main advantage of massive gravitons as dark matter particles is that they only interact gravitationally, so they can avoid trying to detect their presence,” said Cacciapalla.
In contrast, other proposed dark matter candidates – such as weakly interacting massive particles, axions and neutrinos – can also be felt through their very subtle interactions with other forces and fields.
The fact that massive gravitons hardly interact via gravity with other particles and forces in the universe provides another advantage.
“Due to a very weak interaction, they decay so slowly that they remain stable throughout the life of the Universe,” said Cacchapalla. “For the same reason, they are slowly formed during the expansion of the Universe and accumulate there until today.”
In the past, physicists considered gravitons to be unlikely dark matter candidates because the processes that create them are extremely rare. As a result, gravitons will be created at a much slower rate than other particles.
But the team found that in a picosecond (trillionth of a second) after the Big Bang, more gravitons were created than past theories suggested.
This amplification was enough for massive gravitons to fully explain the amount of dark matter we detect in the universe, the study says.
“The increase really came as a shock,” said Cacchapalla. “We had to run a lot of checks to make sure the result was correct, as this leads to a paradigm shift in how we view massive gravitons as potential candidates for dark matter.”
Because massive gravitons form below the energy scale of the Higgs boson, they are free from the uncertainties associated with higher energy scales that current particle physics does not describe very well.
The team’s theory links physics studied at particle accelerators such as the Large Hadron Collider to the physics of gravity.
This means that powerful particle accelerators, such as the Future Circular Collider at CERN, due to start operating in 2035, could be looking for evidence of these potential dark matter particles.
“Probably the best chance we have at future high-precision particle colliders,” said Cacchiapaglia. “That’s what we’re currently investigating.”
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