Unraveling Neutrino Confusion: Ettore Majorana's Theory

[Physics4Eva]

TL;DR

Does anyone know if neutrinos are there own antiparticles? And could there be more than the three known types of neutrinos?

I was looking into neutrinos and found that a man named Ettore Majorana proposed neutrinos and antineutrinos are the same thing. If this could be true, antineutrinos emitted during double beta decay could annihilate one another and vanish. However, this would violate lepton number conservation. Has this been proven?
Also, if neutrinos were there own antiparticles, would that explain the disappearance of antimatter in the universe?
Another thing I heard was that oddities in neutrino experiments have been found which may suggest that there are different neutrino interactions or neutrinos. What would this mean to science or engineering?

Thanks

 

[Vanadium 50]

Does anyone know if neutrinos are there own antiparticles?

No.

And could there be more than the three known types of neutrinos?

Not if they are "active", i.e. interact with matter via the weak force. There are exactly three. One is free to postulate non-interacting "sterile" neutrinos, just as one is always free to do so for non-interacting particles.

 

[Orodruin]

If this could be true, antineutrinos emitted during double beta decay could annihilate one another and vanish. However, this would violate lepton number conservation. Has this been proven?

No. However, searches for neutrinoless double beta decay are ongoing.

Also, if neutrinos were there own antiparticles, would that explain the disappearance of antimatter in the universe?

Not on its own. However, many models that predict neutrinos to be Majorana particles also offer possibilities to engineer a situation that results in a baryon asymmetry in the early Universe (a process known as baryogenesis via leptogenesis, see, e.g., https://arxiv.org/abs/hep-ph/0608347v1).

Another thing I heard was that oddities in neutrino experiments have been found which may suggest that there are different neutrino interactions or neutrinos. What would this mean to science or engineering?

Please give appropriate references. "A thing I heard" is very vague.

 

[Physics4Eva]

Please give appropriate references. "A thing I heard" is very vague.
[/QUOTE]
I heard about this experiment called Liquid Scintillator Neutrino Detector(LSND). Apparently, the experiment made no sense in relation to other neutrino experiments such as Super-K in terms of oscillation. Basically the experiment suggested that there was a fourth neutrino that couldn't be detected because it lacked the interactions that made other neutrinos detectable. The experiment indirectly showed that neutrinos were oscillating through this "sterile neutrino".
Following this were experiments using nuclear reactors which produced numbers that couldn't be easily explained without a sterile neutrino. Another follow up experiment was MiniBooNE which seemed to come in alignment with LSND. The MiniBooNE experiment fired muon neutrinos into the dirt towards an underground detector that detects the arrival of electron neutrinos in case muon neutrinos are shape-shifting. More electron neutrinos than other neutrino models. This suggested that some muon neutrinos shape-shift by oscillating through a sterile neutrino.
Sorry about the confusion and thanks for the insight.

 

[Orodruin]

The LSND anomaly remains unexplained. The interpretation in terms of sterile neutrinos is quite disfavoured in the community due to conflict with other experiments. The MiniBooNE results are curious in their own right. I think it is fair to say that sterile neutrinos in the required mass range are viewed with some skepticism in the community, but people are still doing work in that direction.

 

[Physics4Eva]

Thanks, but would you say that a fourth neutrino type is possible based on these experiments?

 

[mfb]

You cannot rule out a fourth neutrino. If the couplings (or mixing parameters) are small enough then you'll never see a difference to the case of just three neutrinos.

 

[Orodruin]

Thanks, but would you say that a fourth neutrino type is possible based on these experiments?

You cannot rule out a fourth neutrino. If the couplings (or mixing parameters) are small enough then you'll never see a difference to the case of just three neutrinos.

This is why we typically talk about eV-scale sterile neutrinos when discussing the type of neutrinos that would be required to solve the LSND anomaly. That requirement also comes with a range for the mixing angle required. Sterile neutrinos that solve the LSND anomaly are in strong tension with other experiments (in particular muon neutrino disappearance such as in atmospheric neutrinos).

 

[Physics4Eva]

Cool, thanks guys!