Big Bang neutrinos : dark matter Aug 31, 2018 22:55:17 GMT -8
Post by davesenesac on Aug 31, 2018 22:55:17 GMT -8
7 December 2002 snippet:
BY THE time you have read this sentence, over a trillion neutrinos will have passed through your body. These particles are one of the most pervasive forms of matter in the Universe: they are created in the Sun and in supernovas, by cosmic rays crashing into the upper atmosphere, and they are even made on Earth, streaming out from nuclear reactors and radioactive rocks.
Yet neutrinos are also the most elusive type of matter. Most of them pass straight through you without noticing a single atom of your body. Indeed they pass through the Earth and the stars virtually unhindered, taking with them all the information they carry.
And that information, it seems, is something that physicists would love to get their hands on. In the past decade, researchers have found growing evidence that neutrinos misbehave in ways that contradict our best theories of how the Universe works. These findings are forcing physicists to abandon their most cherished ideas about neutrinos: that they have no mass and can travel through space at the speed of light. And the alternatives are raising profound new questions about the nature of matter and even the structure and future of the entire Universe.
Serious doubts about the nature of neutrinos first emerged from studies of the Sun. Solar physicists have a deep understanding of our nearest star. They know that the fusion processes at its heart produce electron neutrinos – uncharged relatives of the electron, and one of the three known types of neutrino. The other two types are the muon neutrino and the tau neutrino, which are related to the…
Nuclear forces treat electrons and neutrinos identically; neither participate in the strong nuclear force, but both participate equally in the weak nuclear force. Particles with this property are termed leptons. In addition to the electron (and it's anti-particle, the positron), the charged leptons include the muon (with a mass 200 times greater than that of the electron), the tau (with mass 3,500 times greater than that of the electron) and their anti-particles.
Both the muon and the tau, like the electron, have accompanying neutrinos, which are called the muon-neutrino and tau-neutrino. The three neutrino types appear to be distinct: For instance, when muon-neutrinos interact with a target, they will always produce muons, and never taus or electrons. In particle interactions, although electrons and electron-neutrinos can be created and destroyed, the sum of the number of electrons and electron-neutrinos is conserved. This fact leads to dividing the leptons into three families, each with a charged lepton and its accompanying neutrino...
Supernovae too are predominantly a neutrino phenomenon, because neutrinos are the only particles that can penetrate the very dense material produced in a collapsing star; only a small fraction of the available energy is converted to light. It is possible that a large fraction of the dark matter of the universe consists of primordial, Big Bang neutrinos.