Darkish matter, the elusive substance that accounts for almost all of the mass within the universe, could also be made up of huge particles referred to as gravitons that first popped into existence within the first second after the Large Bang. And these hypothetical particles may be cosmic refugees from further dimensions, a brand new principle suggests.
The researchers’ calculations trace that these particles may have been created in simply the fitting portions to clarify dark matter, which may solely be “seen” by way of its gravitational pull on bizarre matter. “Large gravitons are produced by collisions of bizarre particles within the early universe. This course of was believed to be too uncommon for the large gravitons to be darkish matter candidates,” examine co-author Giacomo Cacciapaglia, a physicist on the College of Lyon in France, advised Reside Science.
However in a brand new examine printed in February within the journal Physical Review Letters (opens in new tab), Cacciapaglia, together with Korea College physicists Haiying Cai and Seung J. Lee, discovered that sufficient of those gravitons would have been made within the early universe to account for all the darkish matter we at present detect within the universe.
The gravitons, in the event that they exist, would have a mass of lower than 1 megaelectronvolt (MeV), so not more than twice the mass of an electron, the examine discovered. This mass stage is properly under the dimensions at which the Higgs boson generates mass for bizarre matter — which is vital for the mannequin to provide sufficient of them to account for all of the darkish matter within the universe. (For comparability, the lightest recognized particle, the neutrino, weighs lower than 2 electronvolts, whereas a proton weighs roughly 940 MeV, in response to the National Institute of Standards and Technology (opens in new tab).)
The crew discovered these hypothetical gravitons whereas trying to find proof of additional dimensions, which some physicists suspect exist alongside the noticed three dimensions of house and the fourth dimension, time.
Within the crew’s principle, when gravity propagates by way of further dimensions, it materializes in our universe as huge gravitons.
However these particles would work together solely weakly with bizarre matter, and solely by way of the pressure of gravity. This description is eerily much like what we find out about darkish matter, which doesn’t work together with mild but has a gravitational affect felt in all places within the universe. This gravitational affect, for example, is what prevents galaxies from flying aside.
“The principle benefit of huge gravitons as darkish matter particles is that they solely work together gravitationally, therefore they’ll escape makes an attempt to detect their presence,” Cacciapaglia mentioned.
In distinction, different proposed darkish matter candidates — resembling weakly interacting huge particles, axions and neutrinos — may also be felt by their very refined interactions with different forces and fields.
The truth that huge gravitons barely work together by way of gravity with the opposite particles and forces within the universe gives one other benefit.
“Attributable to their very weak interactions, they decay so slowly that they continue to be steady over the lifetime of the universe,” Cacciapaglia mentioned, “For a similar purpose, they’re slowly produced throughout the growth of the universe and accumulate there till immediately.”
Up to now, physicists thought gravitons had been unlikely darkish matter candidates as a result of the processes that create them are extraordinarily uncommon. Consequently, gravitons could be created at a lot decrease charges than different particles.
However the crew discovered that within the picosecond (trillionth of a second) after the Big Bang, extra of those gravitons would have been created than previous theories steered. This enhancement was sufficient for large gravitons to utterly clarify the quantity of darkish matter we detect within the universe, the examine discovered.
“The enhancement did come as a shock,” Cacciapaglia mentioned. “We needed to carry out many checks to be sure that the outcome was right, because it leads to a paradigm shift in the way in which we take into account huge gravitons as potential darkish matter candidates.”
As a result of huge gravitons type under the power scale of the Higgs boson, they’re free of uncertainties associated to increased power scales, which present particle physics does not describe very properly.
The crew’s principle connects physics studied at particle accelerators such because the Large Hadron Collider with the physics of gravity. Which means that highly effective particle accelerators just like the Future Round Collider at CERN, which ought to start working in 2035, may hunt for proof of those potential darkish matter particles.
“In all probability the very best shot we’ve got is at future high-precision particle colliders,” Cacciapaglia mentioned. “That is one thing we’re at present investigating.”
Initially printed on Reside Science.