About neutrino anomalies

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  • #26
Orodruin
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Are sterile neutrinos out the window? IceCube seems to have severely constrained them, but I'll admit I'm not aware of what range might be left for them to inhabit.
It depends a bit on what you put into the concept of ”sterile neutrino”. Sterile neutrinos with eV scale masses (which is a common interpretation of the term) are severely constrained. However, the heavy right-handed neutrinos of the seesaw are arguably also ”sterile” ...
 
  • #27
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It depends a bit on what you put into the concept of ”sterile neutrino”. Sterile neutrinos with eV scale masses (which is a common interpretation of the term) are severely constrained. However, the heavy right-handed neutrinos of the seesaw are arguably also ”sterile” ...
In my previous post, I am referring to leptons that oscillate to some extent with the Standard Model neutrinos, but otherwise have no interactions via the strong, weak or electromagnetic forces (although they would, of course, interact via gravity).

For what it is worth, I don't think these exist either, but the observational exclusions aren't nearly as strict for this class of sterile neutrinos.

I am also assuming that these neutral leptons have a mass in excess of 10 eV. This cutoff is important (1) because above that mass (give or take) they cease to register as neutrinos for purposes of cosmology measures of the effective number of neutrino species (i.e. Neff), (2) because they would not be considered in the cosmologically determined sum of neutrino masses, and (3) because a sterile neutrino in this mass range is too massive to fit the main anomalies in neutrino physics alleged to provide an experimental basis for the sterile neutrino hypothesis, which I have explained have been largely discredited for good physics data based reasons.

These would instead primarily serve as dark matter candidates, although they would have to be formed via a means other than thermal freeze out because otherwise they would constitute "hot dark matter" which is inconsistent with the high amount of observed small scale (i.e. galaxy scale) structure in the Universe.

Since they are truly sterile, they would have no cross-section of interaction with protons or neutrons or electrons and hence would evade direct detection experiments.

The main parameter space sweet spot would be sterile neutrinos with a keV order of magnitude "warm dark matter" mass, but warm dark matter models without self-interaction still struggle mightily to produce the observationally inferred shape of dark matter halos in galaxies and galactic clusters.

I am not considering heavy right-handed neutrinos in seesaw models.
 
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Orodruin
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In my previous post, I am referring to leptons that oscillate to some extent with the Standard Model neutrinos, but otherwise have no interactions via the strong, weak or electromagnetic forces (although they would, of course, interact via gravity).

For what it is worth, I don't think these exist either, but the observational exclusions aren't nearly as strict for this class of sterile neutrinos.

I am also assuming that these neutral leptons have a mass in excess of 10 eV. This cutoff is important (1) because above that mass (give or take) they cease to register as neutrinos for purposes of cosmology measures of the effective number of neutrino species (i.e. Neff), (2) because they would not be considered in the cosmologically determined sum of neutrino masses, and (3) because a sterile neutrino in this mass range is too massive to fit the main anomalies in neutrino physics alleged to provide an experimental basis for the sterile neutrino hypothesis, which I have explained have been largely discredited for good physics data based reasons.

These would instead primarily serve as dark matter candidates, although they would have to be formed via a means other than thermal freeze out because otherwise they would constitute "hot dark matter" which is inconsistent with the high amount of observed small scale (i.e. galaxy scale) structure in the Universe.

Since they are truly sterile, they would have no cross-section of interaction with protons or neutrons or electrons and hence would evade direct detection experiments.

The main parameter space sweet spot would be sterile neutrinos with a keV order of magnitude "warm dark matter" mass, but warm dark matter models without self-interaction still struggle mightily to produce the observationally inferred shape of dark matter halos in galaxies and galactic clusters.

I am not considering heavy right-handed neutrinos in seesaw models.
Sure, I just wanted to make it clear that whether or not steriles are excluded depends on what you put into the concept.
 
  • #29
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I like the theory of neutrino oscillations and it explains a lot, however, I am having difficulty with it as a full solution, here is why;
the Solar neutrino deficit is about 2/3 yet There are only two flavors of Solar neutrinos. I would expect the Solar deficit to be closer to 1/2 or something other than 2/3. This value indicates that the dispersion of three neutrino flavors is basically flat regardless of the detectors proximity to a large neutrino source, like the Sun.
also, it seems to me that the neutrino mass change should progress from lightest to heaviest with an accompanied decrease in speed. It should not progress from heaviest to lightest as this would require the speed to increase, I cannot see any example where this occurs in other phenomenon.
either way, this sequence should disrupt the flavor ratio.
just a few thoughts on the matter.
 
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  • #30
Vanadium 50
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You have numbers in that post. Do you have calculations to go along with them?
 
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No, I just tried to keep it simple
 
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  • #32
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So, you don't do a calculation but guess at an answer. and when your guess doesn't match reality, it's not that your guess is wrong, it's that neutrino oscillations are a bad theory.

I am unconvinced.
 
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Not at all, I am just trying to understand the concept, I did not mean to ruffle your feathers
 
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Orodruin
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I would expect the Solar deficit to be closer to 1/2 or something other than 2/3. This value indicates that the dispersion of three neutrino flavors is basically flat regardless of the detectors proximity to a large neutrino source, like the Sun.
This is wrong. The mechanism at work here is the Mikheev-Smirnov-Wolfenstein effect and adiabatic flavor transitions. The MSW matter effect on oscillations imply that neutrinos exit the Sun almost entirely in the second mass eigenstate (provided that they are energetic enough to be produced above resonance). This in turn means that the nu_e survival probability is based almost exclusively on the nu_e content of that mass eigenstate.

It is also wrong that only two flavors are involved. Theory predicts almost equal numbers of mu and tau neutrinos.

It is not the case that oscillations equilibrate the flavors. The oscillation probabilities depend on several things, including the mixing parameters.

also, it seems to me that the neutrino mass change should progress from lightest to heaviest with an accompanied decrease in speed. It should not progress from heaviest to lightest as this would require the speed to increase, I cannot see any example where this occurs in other phenomenon.
This is well known (assuming fixed momentum) and it does not really affect oscillations until wave packets of different mass eigenstates separate which would just average out the oscillations. This does happen for solar neutrinos but as mentioned they effectively only consist of one mass eigenstate anyway so it is not super relevant.

Note: Neutrinos will not change their speed during propagation. They are in a quantum mechanical superposition of their mass states and it is the mass states that move at different velocities.

Not at all, I am just trying to understand the concept, I did not mean to ruffle your feathers
You’re not though. You are making assumptions of how things behave and try to draw conclusions based on those (faulty) assumptions. That will never end well and you will not really learn anything. What you should be doing if you wish to understand is to pick up some reference literature on the subject. For example, section III.G of this review.
 
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