Breaking news! Positive matter can exist because of neutrinos, which reshuffle the positive and antimatter!

Scientific research continues to surprise, and now a new study by an international team of researchers shows that gravitational waves, ripples in space-time, may contain another piece of evidence that matter survived the Big Bang because of a phase transition that allowed neutrinos to reshuffle matter and antimatter. How everything was saved from a complete destruction is not a question in science fiction or Hollywood movies. According to the Big Bang theory of modern cosmology, there should have been an equal amount of matter and antimatter if they had remained that way.

Matter and antimatter should eventually meet and annihilate one-to-one, leading to complete annihilation. Then the universe will be empty, and there will be no galaxies, stars, black holes, planets, and billions of species of life on Earth! However, the existence of all things in the universe contradicts this theory. In order to overcome the complete annihilation of positive and antimatter, the universe must convert a small amount of antimatter into (positive) matter, causing an imbalance between positive and antimatter. Theoretical studies have shown that the required imbalance is only one billionth, but when and how this imbalance is caused remains an unknown mystery.

"Once we look back to the first million years or so of the universe's existence, it becomes opaque to light, which makes the fundamental question of 'Why are we here?' very difficult to answer," said study co-author Jeff Dror, a postdoctoral researcher at the University of California, Berkeley, and a physics researcher at Lawrence Berkeley National Laboratory. "Because matter and antimatter have opposite charges, they cannot be transformed into one another unless they are electrically neutral. Neutrinos are the only electrically neutral matter particles we have, so they are the strongest contender to accomplish this mission."

One theory supported by many researchers is that the universe went through a phase transition so that neutrinos could reshuffle matter and antimatter. Phase transitions are like boiling water turning into steam, or cooling water into ice, where the behavior of matter changes at a specific temperature called the critical temperature. When a certain metal is cooled to a lower temperature, it completely loses its resistance through a phase transition and becomes a superconductor, which is also the basis of magnetic resonance imaging (MRI) or magnetic levitation technology for cancer diagnosis, and can also make trains float, allowing them to run at speeds of 480 kilometers per hour without causing dizziness.

"Like superconductors, phase transitions in the early universe may have created very thin tubes of magnetic fields called cosmic strings," explained study co-author Hidefumi Murayama, UC Berkeley's McAdams Professor of Physics, principal investigator at the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo, and senior faculty scientist at Lawrence Berkeley National Laboratory. The researchers believe the cosmic strings then tried to simplify themselves, leading to tiny ripples in spacetime called gravitational waves. For almost all possible critical temperatures, future space observatories:

These temperatures can be detected by missions such as LISA, BBO (European Space Agency) or DECIGO (Japan Aerospace Exploration Agency). Graham White, co-author of the study, said: "The discovery of gravitational waves gives us a new opportunity to look further back in time, because the universe was "transparent" to gravity from the very beginning. When the temperature at the beginning of the universe was probably one trillion to one quadrillion times higher than the hottest place in the universe today, the behavior of neutrinos was likely the way to ensure the existence of positive matter in the universe."

The study proves that there may also be a detectable background of gravitational wave ripples left behind. Cosmic strings were once popular as a way to create tiny changes in the density of mass that eventually became stars and galaxies, but it died out when data from previous studies ruled out the idea. "Now, with the new research, the idea is back for different reasons, which is exciting!" said Takashi Hiramatsu, a postdoctoral researcher at the Institute for Cosmic Ray Research at the University of Tokyo, whose institute is responsible for Japan's gravitational wave detectors KAGRA and the Super-Kamiokande experiment.

Kazunori Kohri, associate professor at the Theoretical Center of the Japan High Energy Accelerator Research Organization, said: "The spectrum of gravitational waves from cosmic strings is very different from the spectrum of astrophysical sources such as black hole mergers, so it is entirely possible that this source is indeed cosmic strings. It would be very exciting to know why positive matter in the universe exists. This is one of the ultimate questions in science!" The research results have been published in the journal Physical Review Letters as an editor's recommendation.

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Bo Ke Yuan | Research/From: Kavli Institute for the Physics and Mathematics of the Universe

Reference journal: Physical Review Letters

DOI: 10.1103/PhysRevLett.124.041804

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