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Tom Mazanec
2012-Nov-17, 06:41 PM
Even though neutrinos change type among the three types (which IIRC is the proof of neutrino mass) could they be massless? Is there a reason why it is ABSOLUTELY impossible for a massless particle to change? If so, what is it? If neutrinos must have mass, do we have lower limits on what it is? What are the upper limits?

Shaula
2012-Nov-17, 07:19 PM
Actually the masses of the neutrinos are not well defined. The mass eigenstates of the neutrino mixture are not the same as the flavour eigenstates to add a greater complication to the model. As I understand it the conservation laws mean that it starts off as a flavour eigenstate. However the fact that the mass and flavour eigenstates are not the same means that the phase of each changes at a different rate. The difference in phase is dependent on masses, so for zero mass you get zero difference in phase and the beam stays in the initial flavour eigenstate.

ShinAce
2012-Nov-17, 07:31 PM
Even though neutrinos change type among the three types (which IIRC is the proof of neutrino mass) could they be massless? Is there a reason why it is ABSOLUTELY impossible for a massless particle to change? If so, what is it? If neutrinos must have mass, do we have lower limits on what it is? What are the upper limits?

The last limit I saw was from:
http://arxiv.org/abs/0909.2104
about 2 eV/c2 where an electron is 511000.

The idea is that if they're massless, they don't experience time and can't oscillate. The problem is, they travel through matter paths. Without knowing more about the flavor oscillations, it's hard to tell what causes it.

Plus the Higgs mechanism does not give us the neutrino masses. Ain't that a bummer!

Ivan Viehoff
2012-Nov-19, 11:47 AM
In strictly scientific terms, we will not be sure that they do have a mass until we do manage to demonstrate it directly. But given the ceiling placed upon their mass, this will be very hard. But if they are massless, then our theories of matter are very wrong, and no one has devised plausible alternative theories of matter that allow them to be massless. It can also be said that there are some inconsistencies in our theories of matter, and no one has devised plausible alternative theories of matter that fix those inconsistencies.

trinitree88
2012-Nov-19, 07:53 PM
In strictly scientific terms, we will not be sure that they do have a mass until we do manage to demonstrate it directly. But given the ceiling placed upon their mass, this will be very hard. But if they are massless, then our theories of matter are very wrong, and no one has devised plausible alternative theories of matter that allow them to be massless. It can also be said that there are some inconsistencies in our theories of matter, and no one has devised plausible alternative theories of matter that fix those inconsistencies.

Ivan. One of those inconsistencies is Law of Conservation of Electron Family Number. Massive neutrinos could at least in principle allow you to travel in a clever spaceship faster in this reference frame than them, allowing you to overtake them while their handedness remains the same. That would convert a neutrino into an antineutrino by virtue of your definitions, and violate electron family number......something that has never been seen in a particle physics lab, and definitely new physics. Won't happen. Born at c, travel at c, die at c...massless, and the conservation Law is good. Betcha a hot fudge sundae and tickets to Cinderella's Ball. pete

In addition the timing of the coincidences from SN 1987A, make them consistent with c to I believe 8 sig figs...pretty good data also.

trinitree88
2012-Nov-19, 07:57 PM
Even though neutrinos change type among the three types (which IIRC is the proof of neutrino mass) could they be massless? Is there a reason why it is ABSOLUTELY impossible for a massless particle to change? If so, what is it? If neutrinos must have mass, do we have lower limits on what it is? What are the upper limits?

Tom, For a massless particle to oscillate en route violates Conservation of Momentum.

Shaula
2012-Nov-19, 08:29 PM
Ivan. One of those inconsistencies is Law of Conservation of Electron Family Number. Massive neutrinos could at least in principle allow you to travel in a clever spaceship faster in this reference frame than them, allowing you to overtake them while their handedness remains the same. That would convert a neutrino into an antineutrino by virtue of your definitions, and violate electron family number......something that has never been seen in a particle physics lab, and definitely new physics. Won't happen. Born at c, travel at c, die at c...massless, and the conservation Law is good. Betcha a hot fudge sundae and tickets to Cinderella's Ball. pete
Actually all that would change would be its helicity. Its chirality would remain the same, no laws would be broken. The chirality is what is important and so a neutrino would not turn into an antineutrino.