All Questions
Tagged with beyond-the-standard-model neutrinos
118 questions
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Neutrino oscillation via some unknown interaction mechanism
My query is based on this post. Similar to the Feynman diagram proposed in the problem, why don't we consider a similar mechanism in beyond standard model to explain the neutrino oscillation? It would ...
- 378
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41
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Can a particle have properties of both Dirac and Majorana particles?
Dirac fermions have antiparticles of opposite properties, and only a particle and an antiparticle can annihilate. Majorana fermions have no antiparticles because they can annihilate with themselves. ...
- 1,537
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1
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42
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Does the number of right chiral neutrinos always need to be the same as the number of anti left chiral neutrinos?
Neutrinos are only observed to have a left handed chirality and anti neutrinos are only observed as having a right chirality. In some beyond the standard model hypotheses neutrinos of right chirality ...
- 377
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125
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Distinction between majorana neutrinos and sterile neutrinos
I am a bit confused about Majorana neutrinos. A generic Dirac spinor can be written in terms of his left and right-chiral components as
$$
\psi = \begin{pmatrix} \psi_L \\ \psi_R \end{pmatrix}
$$
A ...
- 131
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1
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164
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The chirality of the standard model fermions
I read 'The Standard Model Effective Field Theory at Work' by Isidor, Wilsch, and Wyler. In a footnote, they say that, in principle, right-handed neutrinos could be included in the Standard Model by ...
- 311
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1
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169
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Feynman diagram: Two-way arrow in the fermion propagator line?
I have encountered some diagrams (like the example below) where two lines coming out of a single vertex (in this context, right-handed neutrino $N^c$) have opposite direction. In a usual diagram, a ...
3
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1
answer
163
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How do the different Neutrino masses come about?
The determination of the Neutrino mass can be roughly divided in three strategies:
The neutrino mass from cosmological observations:
$$m_\nu = \sum_{i} m_i $$
The neutrino mass from the neutrinoless ...
- 71
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1
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67
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Majorana mass matrix seesaw and renormalizable interactions
Sometimes the general seesaw matrix:
$$\begin{pmatrix} M_L & M_1\\ M_2 & M_R \end{pmatrix}$$
and its just said that in order to get renormalizable interactions one must impose the condition $...
- 6,727
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1
answer
380
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About Majorana neutrinos and chirality
If neutrinos are Majorana particles it is possible that neutrinoless double decay happens, with a diagram like this one:
However it seems to me that this diagram requires the Majorana neutrino to ...
- 131
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0
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134
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Mass matrix for inverse seesaw mechanism
I am having trouble in diagonalizing analytically the mass matrix associated to the inverse seesaw mechanism with lagrangian:
$L= -y_1\bar{L}\tilde{H}N_{R_1} - -y_2\bar{L}\tilde{H}N_{R_2} + N_{R_1}^...
1
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64
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Right-handed neutrinos as dark matter and neutrino bounds
How can right-handed neutrinos evade the SM experimental bound $N_\nu=3$ and become all the dark matter?
- 6,727
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45
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Sterile neutrinos on a theoretical point of view
The results at the BEST experiment strongly suggest that at least one "sterile neutrino" exist.
From the way the experiment is done it is obvious that only the lighter sterile neutrino can ...
- 4,448
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1
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81
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How to find parameters $\theta_{12}, \theta_{13} $ and $ \theta_{23} $ for the lepton mixing matrix?
I am currently studying neutrino physics and read that the PMNS matrix can be expressed through $9$ real parameters. I especially see parameters such as $\sin\theta_{12}$ popping up though, and I don'...
- 115
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1
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86
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What equation does KATRIN use to measure neutrino masses?
Source
KATRIN weighs neutrinos produced by the nuclear decay of tritium, a radioactive isotope of hydrogen. When a tritium nucleus transmutes into a helium one, it ejects an electron and a neutrino (...
- 22.1k
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132
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Right-handed neutrinos Lagrangian and drawing Feynman diagrams from it
The Lagrangian for the right handed neutrino field is:
$$
L_{\nu} = y_{\alpha i} \bar{L_{\alpha}} H^{\dagger} N_{i} + m_{i} \bar{N^{c}_{i}N_{i}}
$$
With $ L_{\alpha} $ being the left-handed lepton ...
- 53
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1
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152
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Difference between right-handed and sterile neutrinos
Several SM extensions propose the addition of heavy, right-handed neutrinos to explain the smallness of neutrino masses. There are also theories adding a fourth, sterile neutrino in the context of ...
- 150
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80
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Neutrino Oscillation and FCNC
We know that in the Standard Model (SM) neutrinos are massless. But the discovery of neutrino oscillation suggests that neutrinos must have masses because only then there will be a mass basis for ...
2
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79
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Number and masses of right-handed neutrinos in the seesaw mechanism
In the Wikipedia article about the seesaw mechanism, it is argued that the seesaw mechanism "extends the Standard Model by assuming two or more additional right-handed neutrino fields", with ...
- 95
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3
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1k
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Is neutrino mass really physics "beyond the Standard Model"?
I took a postgraduate course in "Unification" during my MSc Physics degree. The lecture notes have things like "neutrinos are predicted to be massless" and "neutrino mass ...
- 83
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1
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324
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The neutrinoless double beta decay can only occur if $\dots$
In Wikipedia https://en.wikipedia.org/wiki/Neutrinoless_double_beta_decay#Overview
it says that
The neutrinoless double beta decay can only occur if
(1) the neutrino particle is Majorana, and
(2) ...
- 4,376
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79
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CP violation phases counting in neutrino flavor mixing sector with $N$ sterile neutrinos
In the quark sector, the CKM matrix is obtained from (see p.723 of Peskin QFT)
$$
V_{CKM} =U_u^\dagger U_d = \begin{bmatrix} V_{ud} & V_{us} & V_{ub} \\V_{cd} & V_{cs} & V_{cb} \\
V_{...
- 4,376
2
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1
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397
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PMNS matrix versus CKM matrix -- how precise is the analogy?
PMNS matrix is said to be the matrix for the neutrinos as the CKM matrix for the quarks.
See https://en.wikipedia.org/wiki/Pontecorvo–Maki–Nakagawa–Sakata_matrix#The_PMNS_matrix
However, I am ...
- 4,376
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85
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Flavor mixing Higgs Yukawa term with both left and right chiral neutrinos and with generic masses
In p.727 of Peskin QFT, it derives a flavor mixing Higgs Yukawa term, but he assumes that the neutrinos have no mass.
However we know that we can include both left and right chiral neutrinos, and also ...
1
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0
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681
views
What would a standard model that incorporates the SMASH particles look like?
I'm trying to create a standard model which incorporates the SMASH (Standard Model Axion Seesaw Higgs portal inflation) particles, but I'm having a hard time doing it because I'm unable to find as ...
- 136
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1
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178
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What are the names, charges, and masses, and spins of the 6 new particles proposed in the SMASH standard model of elementary particles?
As you may know, 6 new particles have been proposed to solve a few of the standard model's problems. However, after much of research, I was unable to find the exact names (of the color triplet fermion,...
- 136
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1
answer
67
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Why can't I use just two angles when considering three neutrino oscillation?
I'm just finishing basic particle physics and I just learned about neutrino oscillation. Considering only two neutrinos, one can describe neutrino "mass states" (as we call it) with an angle ...
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0
answers
46
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Possibility of reaching equilibrium starting with a nonequilibrium initial condition in the early radiation-domination
Update after @knzhou's comment
If in a theory, the coupling of the dark matter (DM) field to the Standard Model (SM) fields is small enough, the rate of interaction of the DM particles in the ...
- 27.2k
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37
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Is this equality based on the HDM true?
It is stated in Sterile Neutrinos as Dark Matter that in the HDM model: $$\frac{\mu^2}{m_s}= 92 h^2 \text{eV} \tag{1}$$
where $m_s$ represents the mass of sterile neutrinos and $\mu^2$ represents the ...
- 759
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32
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What is the difference between these mixing-angle equations?
In the following article the mixing angle of the neutrinos is given by:
$$\sin^2 2\theta = \frac{\mu^2}{\mu^2 +[c\Gamma_\alpha E /M +M/2]^2} \tag{1}$$
where $\mu$ represents the Dirac mass , M ...
- 109
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45
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Why would the damping factor of neutrino oscillations be negligible?
In this article the Boltzmann equation for the sterile
neutrinos is simpified to this form:
$$\frac{\partial}{\partial t} f_s (p,t) -H p \frac{\partial}{\partial p} f_s (p,t) \approx \frac{\Gamma_\...
- 759
1
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2
answers
256
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Why is a fourth type of active neutrinos not allowed by the invisible width of the $Z$-boson?
I don't understand the following statement from my notes:
"A fourth active neutrino is not allowed by the invisible width of the $Z$-boson to which it would contribute as much as one active ...
- 759
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1
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500
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What is the relation between energy density ($\Omega$) and the number density of neutrinos ($n$)?
What is the numerical relation between energy density ( $\Omega_\text{s}, \Omega_\alpha$), and the number density of neutrinos (sterile - $n_s$ , active - $n_\alpha$)?
Background info that might help ...
- 759
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51
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What is the reheating temperature of neutrinos during the BBN?
I want to integrate a differential distribution function of sterile neutrinos and the boundaries are the decoupling and the reheating temperature of neutrinos, but I don't know what is an acceptable ...
- 759
9
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3
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451
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Do we have good reasons to believe that neutrino oscillations aren't the result of a new particle? If so, what are they?
The standard way of describing neutrino oscillations seems to be that the mass eigenstates differ from the flavour eigenstates, which leads to an oscillation of neutrino flavour over time.
However, ...
- 93
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0
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177
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How to give left-handed neutrinos alone Majorana mass?
The Wikipedia page on Georgi–Glashow model says
Fermions transforming as a 1 under SU(5) are now thought to be necessary because of the evidence for neutrino oscillations, unless a way is found to ...
- 4,376
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1
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39
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Why does this distribution function depend on time and not temperature?
When reading Sterile neutrino hot, warm, and cold dark matter I came across the following momentum distribution function for a neutrino species $\alpha$:
$$\tag{5.8} f(p,t) = \frac{1}{e^{E(p)/T + \...
- 759
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1
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148
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Why is the neutrino considered a composite particle? [closed]
The existing model predicts it should have no mass but observation says otherwise, it is known that the neutrino can change flavor over time but how does it qualify as a composite particle? Does it ...
- 13.1k
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1
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178
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How do I solve Schroedinger's equation for sterile neutrinos?
When reading Light singlet neutrinos and the primordial nucleosynthesis the following equation is given:
$$\tag{5} i \frac{\partial}{\partial t } \begin{pmatrix} c_e (t) \\ c_x (t) \end{pmatrix}= \...
- 759
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0
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58
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Neutrino oscillations
It seems well documented that neutrinos oscillate between flavours. In the link there are some figures which show probabilities but it isn't clear to me why the abscissa is measured in $L/E$. Is it ...
- 3,906
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226
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What is the meaning of a non-resonant neutrino production?
What is the meaning of non-resonant production in the following context:
They assumed a negligible primordial lepton number,or asymmetry, so
the neutrinos are produced non-resonantly. [1]
I thought ...
- 109
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2
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99
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What are ordinary mass-terms (of neutrinos)?
When reading the introduction to Sterile neutrino hot, warm, and cold dark matter I came across the following definition of sterile neutrinos:
We can define sterile neutrinos generically as spin-$\...
- 759
3
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1
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59
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What causes neutrinos to be weakly coupled?
When reading about "active-sterile mixing", which requires some Dirac mass ($m_D$) and some Majorana masses ($M_R$) to be very small but not zero, the seesaw limit model is discussed ($M_R \gg m_D$).
...
- 759
3
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2
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320
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Why does the observation of $Z$-boson decay imply active neutrinos to be heavy?
Whilst reading Light Sterile Neutrinos: A White Paper it is stated on the bottom of p.3 without an explanation that:
"The observed $Z$-boson decay width implies that any additional active neutrinos ...
- 759
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2
answers
50
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Example of weak interactions induced by mixing
I understand that weak interactions are the exchange of W and Z bosons between leptons and quarks (as explained in this other question: Weak Interaction), but when I read Light Sterile Neutrinos: A ...
- 759
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2
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459
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Is lepton number conserved by definition?
In ordinary beta decay, an electron and an anti-neutrino, together with a proton, are emitted. The proton has zero lepton number, the electron +1 lepton number, and, it is said, the neutrino-type ...
- 141
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149
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Help counting the number of real parameters in simple seesaw Lagrangian
The seesaw Lagrangian is $$-\mathcal{L}_{\rm mass}=\frac{Y^\ell_{ab}\langle H^0\rangle}{\sqrt{2}}\bar{\ell}_{aL}\ell_{bR}+\frac{Y^\nu_{ab}\langle H^0\rangle}{\sqrt{2}}\bar{\nu}_{aL}\nu_{bR}+\frac{1}{2}...
- 12.3k
6
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201
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Does our failure to detect neutrinoless double beta decay spell trouble for the seesaw mechanism?
The seesaw mechanism is a theoretical model of neutrino masses that has the side benefit of (arguably) naturally explaining why neutrinos are so much lighter than the other massive Standard Model ...
- 49.4k
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1
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521
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How do neutrino masses change the shape of the $\beta$ decay spectrum?
It is more-or-less established that neutrinos have masses. But as of now, $\nu$-masses have not been directly measured in the laboratory. But I heard a talk where the speaker said that efforts are ...
- 12.3k
3
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32
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Neutrino flavor models from irreducible representations of discrete groups [duplicate]
I am starting ph.D in neutrino physics-ph. I've read some papers on discrete symmetries and neutrino mass models. Neutrino flavor models are built using irreducible representations of discrete groups, ...
6
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3
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1k
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Does theory allow that one neutrino is massless and the other two not?
The question says it all. Is there the theoretical possibility that one of the neutrino mass eigenstates have zero mass, whereas the other two have not? Is there a theory that allows this option?
I ...
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