Neutrinos, Neutrinos Everywhere...[1]
Open a particle physics text book from the 1960's, 70's or 80's or maybe even the 90's and there's a good chance you'll see two massless particles mentioned, the Photon and Neutrino. At this point, it is now probable that those textbooks are wrong, the neutrino probably has mass, very very small mass. How small, well, scientists don't know yet, but when a particle has mass, even a small amount, there are consequences.
1. Particles with mass can travel slower than the speed of light (Massless particles travel c). The consequence? There are probably slow moving neutrinos (as well as the more common fast moving neutrinos). In other words, they can be slowed down. Remember though, mass is essentially the resistance of an object to acceleration, so low mass means "easily accelerated". So there probably aren't a ton. However early universe neutrinos that were around during the inflationary period probably could have slowed down considerably (redshifting of their de Broglie wavelengths).
2. Neutrinos oscillate between lepton flavor. Got a Tau neutrino? Well, soon it may be a Muon neutrino or a Electron neutrino. In fact, this was one of the first clues they might have mass. Why oscillate and not decay? I'm not sure of the distinction. I'm reading and trying to understand.
http://physicsworld.com/cws/article/news/3064
Here is the experiment that has recently changed "maybe" into "probably" when it comes to neutrinos having mass.
http://news.discovery.com/space/physicists-observe-neutrino-quick-change-in-japan-110625.html#mkcpgn=rssnws1
Neutrinos with mass opens the door for a possible new type of stellar object, the Neutrino Star.
Exciting times in particle physics.
[1] A nod to The Rime of the Ancyent Marinerea by Samuel Taylor Coleridge. The fact that there are neutrinos all around us and yet they are so hard to detect can be very frustrating for the scientists trying to study them.
Neutrinos Probably Have Mass
Re: Neutrinos probably have mass
