Unknown particle could account for missing antimatter

The Universe contains more matter than antimatter, an observation that conflicts with the standard model of physics. Now a group of physicists from Zewail City of Science and Technology in Egypt and the University of Guanajuato in Mexico propose that string theory – which suggests that strings vibrating in 10 dimensions underpin the observable Universe – could offer an explanation.

As it stands, the standard model of physics predicts the formation of an equal number of particles and antiparticles soon after the Big Bang. But an equal number of particles opposite in charge but with the same mass would nullify each other and halt the structures in the universe from forming.

To explain this discrepancy, some physicists have proposed the existence of a type of particle they dub a 'right-handed neutrino'. This theoretical particle is predicted to break down into particles, but not antiparticles – leading to the formation of more matter than antimatter.

The trouble with this theory is it would also mean that these right-handed neutrinos would interact with matter to create antiparticles. If the formation of antiparticles matched the decay of right-handed neutrinos then they would wipe out this desired excess matter.

But now, the team of researchers has shown that, if structures predicted by string theory, called "branes", exist, they would cause the infant universe to expand at a faster rate for a short, but crucial, window of time, just 10-12 seconds after the Big Bang, when these decays happen. This makes it more likely for the right-handed neutrinos to decay, forming the required matter, and less likely to produce antimatter.

"This idea can be confirmed experimentally, if right-handed neutrinos are discovered at the Large Hadron Collider," explains co-author David Delepine, referring to the particle accelerator situated near Geneva, Switzerland.

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