Is it true that neutrinos defy physics’ symmetries?
One of the most intriguing questions in neutrino research is whether neutrinos and their antimatter counterparts, antineutrinos, behave similarly. This is a crucial topic; if the answer is no, it could explain how our universe, which is made up entirely of matter, came to be.
Scientists believe that matter and antimatter should have been produced in equal numbers at the beginning of the universe, but they annihilate into pure energy when they encounter. This should have resulted in a universe devoid of life. However, you’ve probably observed all of the matter-based objects in your environment. This type of asymmetry fascinates me. It makes us wonder how this imbalance came to be.
Researchers have developed a mechanism that treats matter and antimatter differently, without conserving the charge and parity elements of CPT. If this is the case, it means that the Big Bang produced somewhat more matter than antimatter.
In 1967, Russian scientist Andrei Sakharov proposed three requirements that must be met for matter and antimatter to be generated at distinct rates. These are the following:
That the number of baryons (three-quark particles) created in a reaction does not have to be conserved
The fact that the charge and parity of particles produced in an interaction do not have to be preserved
These interactions must be thermally unbalanced.
Physicists have looked for particles that do not conserve baryon number and have found some examples, but not on a large enough scale to address the problem. However, if the amount of leptons (the class of particles that includes neutrinos as well as the charged electron, muon, and tau) created in an interaction is not conserved, a variation in the number of baryons can result.
To help explain matter’s supremacy in our world, physicists have been looking for a process that treats leptons and antileptons differently. Leptogenesis is the name for this process. Neutrinos, a type of lepton, are one of the most likely candidates.
Some neutrino theories incorporate heavy right-handed neutrinos that may have existed early in the universe’s existence but have never been seen by science. These could have degraded in such a way that the lepton number was not conserved.
A number of studies, notably NOvA, T2K, and DUNE, will attempt to solve a significant portion of this puzzle. They’ll investigate if neutrinos and antineutrinos have the same charge and parity. If it is discovered that neutrinos do not conserve CP, it may be possible to have a better understanding of how the cosmos developed into what we observe today.
Nature’s symmetries, and whether or not they ever break, are of great interest to physicists. When scientists claim “neutrinos may break CP,” they’re really asking if a certain type of symmetry, charge-parity symmetry, has been broken. Is there a difference in behavior between neutrinos and antineutrinos, and does nature favor one over the other? In terms of neutrino oscillations, this indicates that neutrinos and antineutrinos may oscillate at various rates, which several experiments have hinted at and are looking into.
Neutrino oscillations are defined by “mixing parameters,” which specify how the mass states combine to produce the desired flavor states. (The disparities between the squares of the three mass states are also taken into account when mixing parameters.)
The so-called Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix controls the quantum combination of neutrino mass states that make up the neutrino flavor states.
The mixing matrix can be simplified to four independent components using three flavors (families) of neutrinos. Three “mixing angles” and a CP-violating phase are commonly stated in a handy fashion for experimentalists. Almost all of these mixing characteristics have been measured to some extent, thanks to a variety of neutrino oscillation experiments conducted all around the world with neutrinos from reactors, accelerators, and the sun. The CP-violating phase is the only exception. That phase could have any value, and if it is non-zero, neutrinos and antineutrinos do act differently in unexpected ways, according to scientists.
Scientists have seen “flavor mixing” in neutrinos, but they are not the first type of particle to do so. Quarks, the point-like particles that make up protons, neutrons, and all other nuclei, were discovered to combine in a similar way in the 1960s. The mixing parameters of the quark mixing matrix, also known as the Cabibbo-Kobayashi-Maskawa (CKM) matrix, were measured in a long and storied campaign.
Scientists know that the CKM mixing angles are quite tiny after 30 years of very exact measurements, and that there is a noticeable lack of CP violation, which many had believed would explain the universe’s matter-antimatter asymmetry. The PMNS matrix, on the other hand, has relatively large (perhaps maximal) mixing angles, but the actual values of the mixing angles have yet to be discovered. The drive to conduct more precise measurements is fueled by these huge yet imprecise mixing angles, as such observations could either rule out or support clues of physics outside the Standard Model, bringing us one step closer to comprehending our world.