Theory Neutrinos

Neutrinos are energetic particles found in the Universe at large. Those are extent in a huge number as, for each proton in the Universe, 1 billion neutrinos are found, which means 300 for each 0.4 square inch! Although neutrinos far outnumber all the atoms in the Universe, they rarely interact with matter, which makes detecting them quite a challenge. Neutrinos, which eventually are extremely small subatomic particles, interact with the weak force and gravity only. But this same property lets neutrinos make a fast exit from places where light cannot easily escape such as the core of a collapsing star, and zip across the Universe almost completely unimpeded. Neutrinos are invisible particles, with about no mass as they can cross about any form of matter. One billion neutrinos are crossing your body each second, for example. Neutrinos also can cross through strong magnetic fields, the interstellar gas, the dust clouds in the galaxies, or even the core of a star. Neutrinos are the remains of the Big Bang. Neutrinos comes in three varieties, the electron neutrino, muon neutrino and tau neutrino as the three can change type as they travel. A fourth kind, the 'sterile neutrino' might exist, interacting even more rarely with matter. Varieties of neutrinos are called 'flavors.' Recent findings based on cosmological observations estimate the combined mass of all three flavors at less than a millionth the mass of a single electron. Scientists think that neutrinos are finding their origin from the most energetic and most distant events of the Universe, like quasars, GRBs, supernovae, black holes or galaxy mergers, as they are produced when cosmic rays interact with what is around and yield such particles with no electrical charge and a negligible mass. High-energy neutrinos are journeying just shy of light speed and rarely interact with other matter, allowing them to travel unimpeded across distances. Another variety of neutrinos is less energetic as it is created when cosmic rays are reaching to the Earth's atmosphere. The existence of low-energy neutrinos was finally evidenced by 2014, and the first crucial step in the nuclear reaction that makes the Sun shine. As the solar energy stems from the transformation of two hydrogen protons into deuterium, one of the fused protons then transforms into a neutron, a process that releases a neutrino and a positron (the antimatter counterpart of the electron). The proton–proton reaction accounts for 90% of all solar neutrinos -as our Sun is emitting also other neutrinos- but those have relatively low energy. Such low-energy neutrinos provide a near-instantaneous snapshot of the solar core, since the neutrinos arrive at Earth just 8 minutes after they are created. Electron neutrinos also turn into two other types — tau neutrinos and muon neutrinos — as they travel from the solar core. The Earth is constantly bombarded with neutrinos from the Sun as those from beyond the solar system can be millions or billions of times more energetic. Neutrinos filled the early universe. Neutrinos, according to newer rival theories to Einstein's relativity theory, like the string theory and the loop quantum gravity, might journey at a speed exceeding the speed of light. According to Relativity, having even a small amount of mass means neutrinos should travel slower than light speed. If exceeding, neutrinos' speed could exceed the light speed by 5 parts in a billion trillion

It was French physicist Henri Becquerel and his 1895 discovery of radioactivity, who initiated the study of neutrinos. In 1930, after studying a radioactive process called beta decay, Wolfang Pauli suggested it likely involved a new subatomic particle. Pauli, then, told: 'I just have done something dramatic! I postulated the existence of a particle which one can not detect!' Such extremely light, electrically neutral particles allowed to explain a apparent violation of energy conservation in the decays of certain unstable atomic nuclei. By 1933, Enrico Fermi called those new particles with the name 'neutrino' as he kept searching for those. Neutrino literally means 'small neutral element.' One had then to wait until in 1956 to have a neutrino detected for the first time. Physicists Frederick Reines and Clyde Cowan detected the evidence that neutrinos were interacting in a liquid fluid which was lying beside a nuclear reactor. Neutrinos produced by nuclear reactions inside the Sun's core were first detected in 1968 only. Supernova 1987A, in 1987, in a nearby galaxy, allowed theorists to anticipate that neutrinos, which escape a collapsing star more readily than light, would be the first signal from the new supernova. And hours before 1987A's visible light arrived at Earth, experiments in Japan, the U.S. and Russia detected a brief burst of neutrinos, making the supernova the first source of neutrinos identified beyond the solar system

Neutrinos are of interest in that, one the one hand, that they may be used to give information about objects which are emitting them as on the other hand, due to that they can cross media and objects which cannot be crossed through by other radiations, they can inform about media and physical objects which one never could have thought of! The basis for the detection of neutrinos -like, for example, the AMANDA project, at the South Pole- is to have the whole radiations and particles which are not neutrinos to be screened by the whole mass of the Earth. This way, at the South Pole, scientists can observe the neutinos which crossed through the Earth beginning at the North Pole! Neutrinos are then counted through the 'muon' -a charged particle- they are emitting. When a neutrino is crossing through the Earth and is tumbling upon a proton, it emits that muon. The muon then is emitting itself a blue light, which is termed the 'Cherenkov radiation', which some qualify the optical equivalent of a sonic boom. Such a occurrence is rare however, with less than one neutrino per one million bumping into a proton when running through the Earth, pole to pole! A neutrino could run through a lead block of 1 light-year in width without even running into one of the lead atoms of the block...

A question about the neutrinos is that, according to the theory predicting the number of neutrinos coming from the Sun, one should observe that number from the Earth. That is not the case however! The solar neutrinos problem was eventually found to come from a misunderstanding of neutrinos themselves as they can undergo a change of type in their journey from the Sun, accounting for the difference between predictions and observations. That also led scientists to theorize that neutrinos have a mass indeed, providing them with the sole physics known beyond the Standard Model. Neutrinos are thought to feature three flavors, morphing into one another as they journey from the Sun. A other team of scientists, that time in Japan, by December 2002, was studying neutrinos -anti-neutrinos indeed- as emitted by the Japanese nuclear plants and they found that the number of neutrinos observed was less than the number of neutrinos emitted. In the case of that latter study, they knew very accurately the number of the emitted neutrinos as they came from a nuclear plant and might be accurately counted. That was thus meaning that neutrinos were lost on the way, between the moment when they were emitted and the moment they were observed! Maybe the general view to follow about those questions is that there be a difference between the emitted, and the observed number of neutrinos as that difference maybe is based upon the fact that a neutrino may change its identity. The mass of a neutrino might be one trillionth less that the mass of a hydrogen atom and 0.28 electronvolt. It might, generally, that the abundance of the neutrinos in the Universe does that they have a cumulative effect upon the distribution of matter in there, and thus upon the formation of the Universe large scale structures. Neutrinos, on a other hand, might have had a important role by the 'recombination epoch', one of the early, defining moments of the Universe, in relation with dark matter. Neutrinos also can allow to deepen particles physics beyond the capacity of particle accelerators