Does the odd helium composition of galaxies solve the enigma of cosmological antimatter?

Does the odd helium composition of galaxies solve the enigma of cosmological antimatter?

During the 1920s, the revolution in quantum physics occurred at an incredibly rapid and rapid pace. However, one of its most brilliant contributors, the British Paul Dirac, was not satisfied with the equation he proposed to quantumly describe particles of matter, such as electrons, according to the special theory of relativity. So he proposed another relativistic equation generalizing the Schrödinger equation for the electron discovered in 1928. This is a remarkable breakthrough, the equation accurately describes the spectrum of hydrogen atoms and it automatically predicts the existence of a spin, a rotating top for electrons corresponding to an angular momentum.

But Dirac’s equation also had curious solutions with embarrassingly negative energies, never seen before experimentally. Convinced of the beauty of his equation, Dirac concluded that for every charged particle of matter there exists a double with a charge of opposite sign, an antiparticle of antimatter as it is called today.

In 1928, at the age of only 26, Paul Dirac formulated the equation that bears his name. It took him a whole year to get there! 9 in itI episode of major equations of physicsDiscover the story of Dirac’s equation that predicted the existence of antimatter… A real revolution! © CEA Research

an equation that describes the formation of matter

In fact, Dirac was partly wrong, his equation was not a relativistic generalization of Schrödinger’s equation for an electron (and not even a relativistic generalization of Schrödinger’s equation in general) but a new equation of the field that describes electromagnetism. was added to the already known equations describing it. , It follows from this equation that by applying the same quantization rules as for atoms – and which already apply to electromagnetic fields, for atoms also implies a different spectrum in terms of energy levels, in this case that of light. Quanta, photon – all you can do is actually figure out the negative energy equation and solution.

But, as a result, it can be concluded that, corresponding to the processes of formation of photons, there must exist processes of formation of particles of matter. The positron, the electron’s antimatter, was discovered in cosmic rays by Carl Anderson in 1932, and the antiproton was discovered in 1955 by Emilio Segre and colleagues in accelerator experiments.

Since then, theory and experiment are clear, one can only create charged particles in pairs, a particle and an antiparticle. When the Big Bang theory was accepted from 1965, it also quickly became clear that as much matter as antimatter must have existed. However, here too, theory and experience show that a particle and its antiparticle annihilate to give only photons upon contact.

Ultimately, we have to conclude that we must not exist and that the observable universe must be filled only with photons of fossil radiation, photons resulting from the combined disappearance of matter and antimatter.

Of course, this is not the case, but where did the missing antimatter go, the amount of which should be equal to that of matter, and why did the predicted annihilation not occur? This is the famous puzzle of the missing cosmological antimatter.

CEA physicist Yves Saquin explains what antimatter is. Every particle of matter has a symmetric antiparticle associated with it. Antiparticles do not exist in nature, because when they meet their symmetric particle, they annihilate to give off only radiation. The Big Bang model predicts that as much matter as antimatter was created in the beginning. However, only matter is observable in the universe. Where did the antimatter go? It is to clarify this mystery that fundamental research is interested in studying antimatter and its creation to try to see if it will not have properties different from the symmetric properties of matter. a video co-produced with magician’s soul, © CEA Research

The abundance of antineutrinos explains the lack of helium

There are many possible solutions. For example, one could imagine that a type of antigravity would have pushed particles of matter and antimatter back into two unrelated worlds before they annihilated.

One can still imagine the implications of another new physics that would produce more matter than antimatter. Photons of cosmic radiation would then indicate that there were few more particles than about one billionth of a billionth of matter, so known matter existed at the time of the Big Bang and would be only a tiny remnant of the carnage of particles and antiparticles. Who produced particles of light from cosmic radiation.

This last scenario is the most favored, and theorists have produced so-called baryogenesis models since the 1970s, which explain why there may have been more protons and neutrons than their antiparticles, the brayons, at the time of the Big Bang. So-called leptogenesis scenarios (the electron and its heavier cousins ​​like the muon are part of the lepton family), especially with neutrinos, have also been produced. Examples can be found in the articles available on arXiv.

Most recently, Anne-Catherine Burns, a PhD student in the field of AstroparticlesUniversity of CaliforniaReported in Irvine, USA Via an article from online media Conversation that he and his colleagues had found additional clues in favor of some models of leptogenesis with neutrinos.

These models imply that some types of neutrinos may not have been produced in equal quantities to their antiparticles. During the first seconds and minutes of the Big Bang, the disparity in the number of neutrinos compared to antineutrinos may have changed the abundance of helium relative to hydrogen as part of a process called primordial nucleosynthesis.

Where do protons, neutrons, atoms, matter come from? Learn how matter appeared about 13.7 billion years ago in this animation-video. Various stages in the history of the universe, from the first hydrogen nuclei, also known as protons, to heavy nuclei such as iron, are at the core of the formation of the natural elements present on Earth. a video-animation co-produced with magician’s soul, © CEA Research

Probing cosmological helium, the infinitely small particle

This is what Anne-Catherine Burns refers to when she says: ” Physicists believe that nuclei of lighter elements such as hydrogen and helium began to form just one second after the Big Bang. This process is known as Big Bang Nucleosynthesis. The nuclei that formed were composed of approximately 75% hydrogen nuclei and 24% helium nuclei, as well as a small amount of heavier nuclei. The most widely accepted theory by the physics community on the formation of these nuclei tells us that neutrinos and antineutrinos, in particular, played a fundamental role in the formation of helium nuclei. Helium was formed in two stages in the early universe. First, neutrons and protons interact with each other in a series of processes involving neutrinos and antineutrinos. When the universe cooled, these processes stopped and the proton/neutron ratio was established. ,

So Burns and his colleagues made unprecedented and improved observations of helium abundances in distant and ancient galaxies monitored by instruments on the Japanese Subaru telescope in Hawaii. It appears that the ten galaxies studied have less helium than predicted by the standard model of primordial nucleosynthesis.

The discrepancy is currently weak, yet far beyond the 5 sigma that the researchers call in their jargon, necessary to declare a discovery and which means there is only one chance in a million or more that the measurement has Fluctuation mimics an effect that does not occur by chance.

So there’s still a lot of work to be done but clearly this is a research topic to keep an eye on.

We can reassure ourselves of this by remembering the following story from years ago by the late astrophysicists David Schramm and Gary Steigman, who concluded from known primordial helium nucleosynthesis data that there must be only three families of light neutrinos in the universe. .

The at first somewhat skeptical scientific community was faced with the facts at CERN in 1989 when the LEP, together with the collision of electrons and positrons and by studying the decay of Z bosons of electroweak theory, verified that there were in fact only three families of light. of neutrinos.





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