New "Ghost Particles" Data Hints At Why The Universe Is Not Made Of Antimatter

According to the laws of physics, matter and antimatter behave the same way and were formed in equal quantities in the Big Bang. When matter and antimatter interact, they annihilate, turning into pure energy. Those two facts suggest that the universe should have nothing in it but energy. As you can see, this is not the case, but we do not know why. A new hint for the true reason might come from neutrinos.

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Neutrinos are known as the "ghost particles" as they can travel through matter, hardly ever interacting with it. Every second, 100 trillion neutrinos are flowing through us, and we are none the wiser. This is not the only peculiarity. There are three known types of neutrinos in the universe and each type is called a flavor: electron neutrinos, muon neutrinos, and tau neutrinos. But neutrinos can change flavor spontaneously, something known as neutrino oscillations.

If this were not weird enough, neutrinos have tiny masses that are formed by a combination of “mass states”: basically, the mass of a single neutrino is a combination of these states, but they do not map to the flavors. Each flavor can be a mix of the three mass states, and they can be in normal ordering or inverted ordering. In normal ordering, you have two light states and one heavy state; in inverted ordering, you have two heavy states and one light one. That’s where things start getting interesting.

If the mass states are in normal ordering, then it is more probable that muon neutrinos will oscillate to electron neutrinos and there's a lower probability that muon antineutrinos will oscillate to electron antineutrinos. In inverted ordering, the opposite happens.

Two different neutrino experiments, the T2K in Japan and NOvA in the United States, have for the first time combined datasets. They have better precision on the mass differences between the mass states (you can’t measure the mass directly, only the difference: did we mention that neutrinos are weird?!). They also found that there is no clear preference for mass ordering. But if inverted mass ordering is correct, the data suggests that this might be a crucial reason why the universe is made of matter.

The finding is not proof, but an intriguing hint. More work is necessary to establish if this will become a fruitful line of research in the field of matter-antimatter asymmetry or peter out once more data comes in.

“Neutrino physics is a strange field. It is very challenging to isolate effects,” Kendall Mahn, co-spokesperson for T2K, said in a statement seen by IFLScience. “Combining analyses allows us to isolate one of these effects, and that’s progress.”

The study is published in the journal Nature.