Dark matter could be a cosmic relic from extra dimensions

[fred8615]

Dark matter, the elusive substance that accounts for the majority of the mass in the universe, may be made up of massive particles called gravitons that first popped into existence in the first moment after the Big Bang. And these hypothetical particles might be cosmic refugees from extra dimensions, a new theory suggests.

The researchers' calculations hint that these particles could have been created in just the right quantities to explain dark matter, which can only be "seen" through its gravitational pull on ordinary matter. "Massive gravitons are produced by collisions of ordinary particles in the early universe. This process was believed to be too rare for the massive gravitons to be dark matter candidates," study co-author Giacomo Cacciapaglia, 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(opens in new tab), Cacciapaglia, along with Korea University physicists Haiying Cai and Seung J. Lee, found that enough of these gravitons would have been made in the early universe to account for all of the dark matter we currently detect in the universe.

The gravitons, if they exist, would have a mass of less than 1 megaelectronvolt (MeV), so no more than twice the mass of an electron, the study found. This mass level is well below the scale at which the Higgs boson generates mass for ordinary matter — which is key for the model to produce enough of them to account for all the dark matter in the universe. (For comparison, the lightest known particle, the neutrino, weighs less than 2 electronvolts, while a proton weighs roughly 940 MeV, according to the National Institute of Standards and Technology(opens in new tab).)

The team found these hypothetical gravitons while hunting for evidence of extra dimensions, which some physicists suspect exist alongside the observed three dimensions of space and the fourth dimension, time.

Read more: https://www.livescience.com/dark-matter ... dimensions