Neutrinos are light, uncharged leptons. The neutrino tag should be applied to question relating to neutrino properties or interactions involving neutrinos.

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What's smaller: a neutrino, or a string from string theory [on hold]

I've recently read an article that stated "If an atom were as big as the solar system, a neutrino would be the size of a golf ball". I watch the science channel, and on (I believe) the show How the ...
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2answers
71 views

Can neutrinos interact by the EM interaction and gravity?

A definition of a lepton is: A particle that does not interact by the strong force but does by the 3 other forces.$^1$ Neutrinos are leptons, so from the above definition one would expect it to ...
19
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6answers
2k views

Why does matter/antimatter only produce gamma rays?

According to wikipedia, all antimatter annihilation produces gamma rays (along with potentially other elements). Why specifically Gamma rays? Why not electromagnetic waves of other wavelength?
11
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3answers
499 views

How would cold neutrinos get trapped by stars?

Continuing on from the cool physics Q&A'd on the threads Where are all the slow neutrinos?, Is it possible that all "spontaneous nuclear decay" is actually "slow neutrino" ...
6
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1answer
86 views

Why neutrino is always left handed

Why all neutrinos are always left handed while all anti-neutrinos are right handed.
0
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0answers
30 views

Influence of matter of a star on masses of neutrinos

It is well known that if neutrinos has masses then from Dirac equation it follows that they propagate (in vacuum) as a eigenstates of mass (not as eigenstates of interaction). It's wave function is of ...
16
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3answers
250 views

What does the cosmic neutrino background look like today, given that neutrinos possess mass?

This question is inspired by (or a follow-up to) the threads Where are all the slow neutrinos? and Is it possible that all “spontaneous nuclear decay” is actually “slow neutrino” induced? The cosmic ...
7
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2answers
338 views

Is it possible that all “spontaneous nuclear decay” is actually “slow neutrino” induced?

This thought was inspired by a comment from the current leading answer, by @Sentry, to the question Where are all the slow neutrinos? This [slow-neutrino induced nuclear decay] will still be an ...
46
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2answers
1k views

Where are all the slow neutrinos?

The conventional way physicists describe neutrinos is that they have a very small amount of mass which entails they are traveling close to the speed of light. Here's a Wikipedia quote which is also ...
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1answer
31 views

Constructing singlet from doublets

Can we construct a gauge invariant term using the SU(2) doublet $l_L=(\nu_e e)^T$ and $(l_L)^c=C\bar{l}^T_L$? Since, both are doublets under SU(2), and $2\times 2=3+1$, I wonder what will be the ...
6
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1answer
87 views

Do neutrinos interact not quite so weakly?

It is often quoted that most of the solar neutrinos passing through earth do just that – pass through – without interacting. What's generally not said is what fraction of them do interact, and I've ...
1
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0answers
29 views

Do elementary particles with the same weak hyper charge ($-1$) repel each other?

Take an electron neutrino and a muon neutrino for example, they have no electric charge, but both have $-1$ weak hyper charge. So would these two particles repel each other?
0
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0answers
23 views

How does an electron interact with an electron neutrino?

An electron and neutrino come close and they exchange a W boson and then they change places.. but why? A neutrino has no electric charge, so how do they know to interact?
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2answers
42 views

Reference frame for the Cosmic Neutrino Background

It is well known that there exists a reference frame where the total momentum of the Cosmic Microwave Background is zero (a basic fact of special relativity applied to a collection of massless ...
3
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0answers
26 views

Does the vacuum have a zero Seebeck coefficient?

I was considering how at very high energies (e.g the Schwinger Limit) the vacuum starts having properties we would normally associate with "materials", such as non-linear polarizibility. The Seebeck ...
38
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1answer
2k views

Why was the first discovered neutrino an anti-neutrino?

In the search for neutrinos, Cowan and Reines discovered the electron anti-neutrino and named it as such. Why is the particle they discovered the anti-variety? The reason we call electrons 'electrons'...
3
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0answers
69 views

Does this physical situation distinguish whether you are viewing it a mirror?

The weak interaction's lack of $P$-symmetry is often explained by saying that "the amplitudes for processes involving the weak interaction are different from the amplitudes for the same processes ...
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2answers
51 views

Clarification of the concept of Boson Mediator and 'Mediation' in Physics? [closed]

I would like to have a clear concept of Higgs 'mediator' and that 'mediation' speak in physics, what you 'swap' a particle with ...
3
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2answers
126 views

How do they know which flavor was the neutrino if it collapses into an electron or electron-neutrino?

I read an article that talked about how oscillation of neutrinos worked. It caught my attention that the author of the article mentioned that when a neutrino is measured (by the interaction with ...
0
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1answer
43 views

Is it possible that cosmic ray particles and neutrinos account for a significant portion of dark matter?

Sounds a bit naive but I read somewhere that neutrinos were thought to account for dark matter to an extent and I think Zwicki came up with the idea before cosmic rays were announced (not sure though)....
2
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1answer
63 views

How do physicists find the speed of neutrinos?

I have heard that there is evidence for neutrinos traveling close to the speed of light, but how is that done? Since neutrinos barely react with anything, and the only evidence for them is indirect (...
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1answer
55 views

Are neutrinos affected by electromagnetic forces?

I know they don't interact with matter nor any electromagnetic forces, but I know they have mass, very little mass but they have. When something has mass it must be attracted by gravity and other ...
0
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1answer
42 views

Left-handed Majorana mass term forbidden by $SU(2)$?

I'm trying to figure out why a left-handed Majorana mass term is mathematically forbidden by the $SU(2)_L$ symmetry in the context of the seesaw model. As far as I get it, it is because the left ...
4
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1answer
97 views

Photons are self-conjugate but neutrinos may or may not: why is that?

Caution: This may be a very naive question but I find it confusing. Moreover, I believe this question is based on potential misconception. I would like it to be clarified. Although the neutrinos are ...
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1answer
82 views

Inverse beta decay; energy of anti-neutrino

Assuming that the target protons are at rest, calculate the minimum energy of the anti-neutrino for this reaction to take place: $$\bar{\nu}_e+p\rightarrow e^++n$$ I know the answer is given by $E_{\...
0
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3answers
140 views

Why is this particle interaction forbidden?

Why is this interaction forbidden? $$\nu_e+\bar{\nu}_e\rightarrow K^+ + K^-$$ Lepton number is conserved, charge is conserved, baryon number is irrelevant since these are mesons. Energy is conserved ...
4
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1answer
45 views

Measuring the size of the core of the sun with multiple neutrino detectors

Back in 1998, researchers at the Super-Kamiokande neutrino detector released this image: of the sun using their neutrino detector using approximately 500 days of data. This picture covered 90x90 ...
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0answers
27 views

The seesaw mechanism and block-diagonalization

I encounter a description about the diagonization in seesaw mechanism. I think it is somewhat elementary in linear algebra, but I can not understand it well. The description is as follows. In the ...
2
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1answer
45 views

What experimental measurement could be used to show that a neutrino is a Majorana and not a Dirac particle?

I've just been reading something on the concept that neutrinos could be Majorana particles and not Dirac fermions. I was wondering what experimental measurement could show/prove that neutrinos are in ...
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0answers
50 views

Neutrino interaction probability [closed]

Just a quick question, if a single 1GeV neutrino (muon neutrino) were fired at a block of iron with a given density, $\rho$, and the neutrino-nucleon interaction cross section is $\sigma$, what would ...
4
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1answer
47 views

Is there a way of detecting nearby type 1a supernovas?

The SuperNova Early Warning System (SNEWS) consists of several neutrino detectors across the world that can detect the neutrinos generated by a nearby supernova. As I understand, a Type 1a supernova ...
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0answers
25 views

Finding the mixing angle for two-neutrinos

I am trying to answer the following question; Light Majorana neutrino masses can be generated by the see-saw mechanism. Consider a mass term which, in the simplest case of one active and one ...
0
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0answers
21 views

Has a neutrino annihilation ever been recorded?

Can you tell me if an instance of neutrinos annnihilation has ever been observed or provoked? The say this event is very rare, since neutrinos are produced both by beta and inverse beta decay, isn't ...
0
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0answers
25 views

How to calculate probability of neutrino oscillation after a distance

I'm trying to calculate the probability of an detecting a muon neutrino after a certain distance, where the neutrino beam is entirely electron neutrinos as t = 0. I know I need to use the PMNS matrix ...
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1answer
72 views

How to observe neutrinos?

I know that neutrinos are the weakly interacting particles[possibly zero mass] that can pass through matter without any effect which makes them very difficult to detect. But I have heard that they ...
5
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2answers
81 views

Puzzled by a new result on neutrino speeds

In a paper appearing today on arXiv, Wie et al. have used the close coincidence of the time of arrival of gamma rays from GRBs and the detection of single 3-30 TeV neutrinos at the IceCube observatory,...
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1answer
33 views

What direction are the decay particles of muons emitted in?

If I were to run an experiment where I could measure the neutrino as well as the positron emitted when a muon decays, what direction should i be looking in?
0
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0answers
28 views

Majorana neutrino masses from left-handed neutrino condensate?

Let us consider a model with only left-handed neutrinos and with a new-physics interaction between these neutrinos, which leads to their condensation below a certain energy scale. Can we in principle ...
3
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1answer
52 views

Why can the propagation of neutrino mass eignenstates be described by plane wave solutions?

I don't understand why the propagation of neutrino mass eigenstates are given by planewave solutions as expressed in this Wikipedia article. In addition to not being used to thinking in the ...
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1answer
85 views

Do neutrinos have mass? [closed]

I'm really curious on this subject and I want to know if neutrinos have mass. I know they are a subatomic particle, but how much mass.
0
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1answer
87 views

Can a neutrino reach the speed of light?

wikipedia says: Relativistic kinetic energy increases to infinity when approaching the speed of light, thus no massive body can reach this speed. what is a 'massive body': a body more massive ...
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3answers
69 views

How is each neutrino associated with a specific charged lepton?

For instance, why is an electron neutrino called that and what is its relationship with an electron?
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2answers
64 views

Neutrinoless double beta decay: annihilation of neutrinos or nucleon absorption?

I've a question regarding the interpretation of the neutrinos in neutrinoless double beta decay: The basic issue that I have is with papers that regard the decay as a neutrino-neutrino ...
3
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1answer
95 views

How can neutrinos have both mass and helicity?

If a neutrino has mass it must travel at less than the speed of light. So how can it possess helicity, which can change depending on relative velocity?
3
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1answer
78 views

If a neutrino and his antineutrino has different helicity how can it be a possibility that it is a Majorana particle?

All antineutrinos observed thus far possess right-handed helicity (i.e. only one of the two possible spin states has ever been seen), while neutrinos are left-handed. Notwithstanding that it is said ...
1
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1answer
74 views

Why only left-handed neutrinos have been observed yet?

This is what I understood (it may be wrong, so please correct me): since every particle is "divided" into a lefthand and a righthand partner, which is what guarantees the particles to have mass, and ...
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0answers
7 views

Reactor experiments are independent of CP phase

In several papers and also in books I got that the reactor neutrino experiment to measure the value of $\theta_{13}$ is independent of CP violating phases. But what is the reason of it? Why the ...
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1answer
89 views

Neutrinos are slower than gravitational waves according to their mass?

Neutrino bursts are observed before the visible light of supernovas, most famously SN 1987A. Astronomers likewise expect gravitational waves. Gravitational waves are supposed to travel at exactly the ...
4
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4answers
218 views

Is it possible that dark-matter is composed of a large number of neutrinos from the big bang? [duplicate]

They seem to have all the properties of dark-matter (massive, with no electromagnetic interaction). Could it be that many of the neutrinos produced since the big bang have formed massive neutrino ...
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2answers
42 views

Could neutrinos be used to take high resolution pictures of atomic nuclei?

Of course, this is obviously not feasible with modern technology but is it theoretically possible?