Tagged Questions

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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Why aren't purely Dirac neutrinos rules out?

Its common knowledge that in neutrinos can be Dirac particles without any Majorana masses as given a mass matrix, \begin{equation} \left( \begin{array}{cc}\nu _L & \nu _R \end{array} \right) ...
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How do we know that subatomic particles, Quarks, Neutrinos, and even Gluons, are not operating in multiple dimensions? [closed]

We have observed that particles such as Quarks, exist in flavors with mass being different for each, but is it not possible that the dimensional framework of each particle, when it is created, could ...
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1answer
21 views

Lepton flavour violation

I was reading about the evidence of lepton flavour violation coming from the observation of neutrino oscillations, and was wondering whether this could also lead to LVF in weak interactions or not. ...
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Neutrinos and photons

Are neutrinos less 'dense' than photons? I am referring to the fact that neither particle has 'mass' in a conventional sense. In terms of particle interaction, is there a substantial 'size' ...
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1answer
41 views

How do we know what the flavour of the neutrino from a beta decay is?

I have read that because of the conservation of the leptonic number, a neutron should decay into $p + e^- + \overline{\nu}_e$. I don't understand this argument because I have also learnt that the ...
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1answer
58 views

Neutrino-Neutron Interaction Feynman Diagram (W Boson Direction)

I am currently studying differential cross sections for my Nuclear Physics module. I'm looking an experiment where muon-neutrinos are interacting with nucleons in a scintillator producing muons (which ...
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How to construct singlet and other multiplets from two triplets

Let an $SU(2)$ isotriplet operator is given by\begin{equation}\bar{l^c}i\tau_2\vec \tau l=l^T Ci\tau_2\vec \tau l\sim 3\end{equation} and an isotriplet Higgs field \begin{equation}\vec \Delta\sim ...
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Symmetric neutrino mass matrix?

(i) Is there basis in which the $3\times 3$ sub-matrices $m_L$ and $M_R$, of the $6\times 6$ neutrino mass matrix $$m_\nu=\begin{pmatrix}m_L & m_D\\ m_D^T & M_R\end{pmatrix}$$ can be made ...
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Semiclassical approximation in Quantum Field Theory

I've recently stumbled upon a semiclassical approximation to quantum field theory that I've never heard of and have a hard time understanding. Consider the Hamiltonian, \begin{equation} H = \frac{c}{ ...
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1answer
77 views

Neutrinos at Super-Kamiokande

Why did the Super-Kamiokande experiment detect half the number of neutrinos emanating from below the earth as from above it?
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4answers
295 views

A neutrino has rest-mass and travels at (near) $c$, why isn't its mass/ energy (nearly) infinite?

If the total energy of all three types of neutrinos exceeded an average of 50 eV per neutrino, there would be so much mass in the universe that it would collapse. This limit can be circumvented ...
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Beta plus decay [duplicate]

I think I understand beta minus decay: A nucleon loses mass and this mass is converted into an electron and an electron anti-neutrino. Correct? (I imagine there might be some kinetic energy too but ...
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Beta plus decay…explain one thing [duplicate]

Can anyone please explain how, in beta plus decay, a nucleon can gain mass by changing from a proton to a neutron? Where does it get the extra mass from? Does it convert energy in some way? Does ...
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3answers
347 views

How did Pauli and Fermi deduce the existence of the neutrino? [duplicate]

From Wikipedia: The neutrino was postulated first by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum, and angular momentum (spin). In contrast to Niels Bohr, who ...
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2answers
2k views

What exactly do we see on the famous neutrino image of the sun?

An answer to the question If we could build a neutrino telescope, what would we see? contains a link to a neutrino image of the sun by the Super-Kamiokande neutrino detector. There it says that ...
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2answers
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Searching for Big Bang Neutrinos

How is it possible to discover neutrinos from the big bang? Were the neutrinos emitted just before the big bang? Or at the same moment? If they moved outward in all directions, basically unhindered ...
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Resources on Solar Neutrino Physics

For a project I'm doing for an introductory Astrophysics course, I'm trying to understand the nuances of solar neutrino physics. However, most of what is said while explaining neutrino oscillations ...
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What is the composition of the universe's population of neutrinos?

I believe earth-based detectors measure mainly solar neutrinos, which have energies on the MeV scale of nuclear physics, are directed from the sun, and have flavors determined by the sun's nuclear ...
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Is the left-handed neutrino, after seesaw, still the left-handed neutrino?

Reading this question and its answer Seesaw type-1 and integrating out heavy fields The diagonalization of the see-saw is described as going from "interaction basis" right (and left) handed ...
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4answers
999 views

Why are neutrinos more weakly interacting than light?

When people describe neutrino interactions they describe them as rare/infrequent due to the fact that the neutrinos are electrically neutral and have little mass, if any. Well why then is the photon ...
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2answers
264 views

If we could build a telescope to view the cosmic neutrino background, what would we see?

If we could build a neutrino telescope capable of viewing relic neutrinos that decoupled after the big bang, with a similar angular and spectral resolution that is possible now for the CMB, what would ...
3
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2answers
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Why do the $1/2$ factor appear in the Majorana mass Lagrangian?

In case of Dirac neutrino there is no $1/2$ factor in the mass Lagrangian but for Majorana type neutrino there is a half factor in the mass Lagrangian.
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Can neutrinos really travel faster than the speed of light? [duplicate]

A few years ago scientists found that neutrinos were going faster than the speed of light. Then they found some problem with the calculations. I read an article that was made this year about faster ...
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1answer
51 views

Geophysical Effects of Supernova Neutrino Pulse

While neutrinos are generally totally harmless, a supernova produces enough of them at once that the neutrino flux would kill you if you could stand close enough (and not be killed by other means ...
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1answer
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Seesaw type-1 and integrating out heavy fields

Let's assume seesaw 1 type of generation of left neutrino Majorana mass: $$ L_{m} = -G_{ij}\begin{pmatrix} \bar{\nu}_{L}& \bar{l}_{L}\end{pmatrix}^{i}i\sigma_{2}\begin{pmatrix}\varphi_{1}^{*} \\ ...
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About Paschos-Wolfenstein relation (Weinberg angle measuring)

There is Paschos-Wolfenstein relation: $$ \tag 1 \frac{\sigma^{NC}_{\nu_{\mu}} - \sigma^{NC}_{\bar{\nu}_{\mu}}}{\sigma^{CC}_{\nu_{\mu}} - \sigma^{CC}_{\bar{\nu}_{\mu}}} = \frac{1}{2} - ...
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1answer
176 views

Seeing beyond the CMBR with neutrinos?

As I understand it, you can't see beyond the Cosmic Microwave Background Radiation because the plasma of the early universe was opaque to electromagnetic radiation. What if you had a "neutrino ...
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1answer
195 views

Why did the Homestake experiment only detect solar neutrinos?

The Homestake experiment was designed to detect solar neutrinos. In order to shield it from the background, it was set up in a deep underground mine. It was found that the only one third of expected ...
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1answer
170 views

Can a neutrino act as a virtual particle between two electrons to mediate an electron-electron fermonic interaction?

Can a neutrino act as a virtual particle between two electrons to mediate electron-electron fermonic interaction analogous to how a photon acts as a virtual particle between two electrons to mediate a ...
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Active-sterile mixing for KeVins

People sometimes talk about KeV mass sterile neutrinos as a warm dark matter candidate. I think they call them KeVins (horrible name btw). Now, In order for it to be a good dark matter candidate it ...
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2answers
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Isotropic neutrino-lepton scattering

I'm a physics student and I'm attending an introductory course of particle physics. My professor stated that, in center of mass frame, the $\nu_\mu e^- \to \nu_\mu e^-$ elastic scattering has an ...
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Current known *lower* bounds to the neutrino masses?

I started a little bit of Googling around the topic, and found very few information. There are mainly upper limits. I found lower limits only to the rest mass differences of the different neutrino ...
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Double decay $\beta\beta$ observation and neutrino mass

If the double decay $\beta\beta$ will be detected this means the neutrino is a Majorana particle coincident with its antiparticle. At the moment the half life of this decay is put to ...
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1answer
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Derivation of neutrino oscillation phase factor

As we know, the neutrino $\nu_{\alpha}$ with flavor $\alpha=e,\mu,\tau$ is a linear combination of mass eigenstates: $$ |\nu_{\alpha}\rangle=\sum_iU_{\alpha i}|\nu_i\rangle,\quad i=1,2,3 $$ where the ...
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1answer
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No tremendous neutrino-flux for SNIa?

Why do neutrino account for 99% of the energy release for a SN II, while it is not expected to be the case for SN Ia? Is it because the densities are not high enough to induce inverse beta-decay? ...
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1answer
726 views

Icecube experiment at the North pole instead of the South?

Is there a particular reason, why the Icecube experiment has been installed at the South pole and not at the North pole?
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1answer
195 views

What is chirality?

I actually wanted to make the title as "What is the difference between chirality and helicity"? But I didn't do that because I don't understand properly what chirality is. I have gone through this ...
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3answers
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Solar neutrino problem in 1968 and experimental verification of neutrino oscillation in 2001. Why the huge delay?

Solar neutrino deficit was first observed in the late 1960's. And theory of neutrino oscillation was developed in 1967. But,in 2001, the first convincing evidence of solar neutrino oscillation came in ...
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1answer
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Put yourself in the shoes of Wolfgang Pauli (1930): How could Pauli have narrowed the culprit down to one particle, instead of many?

A while ago, during my introductory physics course, my professor purposefully neglected to tell us about the existence of the anti-electron neutrino in beta decay; he made it an assignment(on our ...
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3answers
361 views

Does the Standard Model require neutrinos to be massless?

I am an undergraduate student in Physics, I have a basic understanding of Particle Physics and Quantum Mechanics but none whatsoever of Quantum Field Theory. I know that Neutrino mixing requires ...
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Neutrino mass difference and mixing angles

What are the most recent values of the mixing angles associated with the 3 neutrinos flavors and what are their mass differences? Have they been measured in the first place?
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3answers
2k views

What exactly is an anti-neutrino?

According to the the definition of anti-particles, they are particles with same mass but opposite charge. Neutrinos by definition have no charge. So, how can it have an anti-particle?
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1answer
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Distance and time measurement in the famous Superluminal Neutrinos Experiment

I tried to understand the technical aspects of the OPERA/CERN experiment, but apparently it takes some professional experience. Therefore I would like to ask someone better acquainted with such ...
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Mass eigenstate of neutrinos [duplicate]

Isn't mass a fixed and an intrinsic property of a particle? How can we talk about eigenstates of the mass in the context of neutrinos?
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3answers
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If a neutrino has a rest frame, why can't a photon have a rest frame as well?

Concerning Rest Frame Wikipedia states: For example, in the rest frame of a neutrino particle travelling from the Crab Nebula supernova to Earth the supernova occurred in the 11th Century AD ...
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1answer
76 views

Weak interaction and Neutrino

I have heard that Neutrino is the only particle affected by the Weak Interaction. How is a Neutrino affected by Weak interaction? I would like to ask the detail. Are there any relationships between ...
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0answers
61 views

Which particles can go right through the atom?

Can elementary particles (like the electron, photon, or neutrino ) go through an atom (not the nucleus)?
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1answer
117 views

Why are neutrino and antineutrino cross sections different?

Particularly in the case of Majorana neutrinos, it seems a little odd that the particle and antiparticle would have differing cross sections. Perhaps the answer is in here, but I've missed it: ...
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2answers
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Why are we blind for the era before the recombination?

At recombination, Universe became transparent to electromagnetic radiation after universe expanded enough to cool down to form neutral atoms. Before that, the matter plasma was effectively opaque to ...
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33 views

Will it ever be possible to observe the cosmic neutrino background?

Is there any foreseeable technology which would facilitate the direct observation of the cosmic neutrino background? Would the ability to warp spacetime have any application here?