All Questions
Tagged with beyond-the-standard-model neutrinos
118 questions
27
votes
1
answer
2k
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Neutrino Oscillations and Conservation of Momentum
I would like to better understand how neutrino oscillations are consistent with conservation of momentum because I'm encountering some conceptual difficulties when thinking about it. I do have a ...
- 271
21
votes
3
answers
3k
views
How can neutrinos oscillate though the lepton flavors have differing masses?
Since the total mass-energy for the neutrino presumably does not change when a neutrino changes lepton flavor, though the mass is different, what compensates for the gain or loss of mass? Does the ...
user1332
21
votes
2
answers
5k
views
Neutrino oscillations versus CKM quark mixing
I wish to describe in simple but correct terms the analogy between the Cabibbo–Kobayashi–Maskawa (CKM) and Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrices.
The CKM matrix describes the rotation ...
- 4,463
18
votes
4
answers
3k
views
Why are neutrino oscillations considered to be "beyond the Standard Model"?
Is this just a historical artifact - that the particle physics community decided at some point to call all of the pre-oscillation physics by the name the "Standard Model"? The reason I ask is because ...
- 8,850
11
votes
2
answers
592
views
If neutrinos are disfavoured as DM candidates why aren't axions?
Numerical simulations of observed large-scale structure formation work best with Cold Dark Matter (CDM; see the answer here). Neutrinos are candidates for Hot Dark Matter (HDM), and hence they cannot ...
- 27.2k
11
votes
2
answers
1k
views
Do solar neutrinos actually oscillate between electron, mu and tau?
I was reading up on the history of the solar neutrino problem, and as far as I can understand it, neutrinos supposedly oscillate from one form to another, thus explaining why there were only one-third ...
- 559
9
votes
3
answers
451
views
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
7
votes
1
answer
3k
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Neutrino flavor and mass eigenstates
Neutrions are produced and detected as flavor eigenstates $\nu_{\alpha}$ with $\alpha=e, \mu, \tau$. These states have no fixed mass, but are the combinations of three mass eigenstates $\nu_{k}$ with $...
- 592
7
votes
1
answer
1k
views
Quark mixing vs neutrino mixing, mass eigenstates, weak states and detection
I have some doubts regarding the CKM matrix in the quark sector and PMNS matrix in the leptonic sector. Let us call $(d^\prime, s^\prime, b^\prime)$
the weak basis for quarks and $(d,s,b)$ the mass ...
- 27.2k
6
votes
3
answers
1k
views
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 ...
- 684
6
votes
1
answer
1k
views
What are the Feynman diagrams for neutrino oscillations?
Which Feynman diagrams are at the basis of neutrino oscillations? I find no clear explanation via Google.
- 361
6
votes
2
answers
1k
views
Can a Majorana field $\psi$ be charged under some $U(1)$ with a charge other than zero?
I know Majorana particles have to be electrically neutral because electric charged is conserved.
My question, however, is whether at all a Majorana field $\psi$ be charged under any $U(1)$ (other ...
- 27.2k
6
votes
1
answer
201
views
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
6
votes
1
answer
176
views
Does the Planck Spacecraft end the question of sterile neutrinos?
The 2015 results of the Planck satellite only found evidence of 3 neutrino's with the 4th (sterile neutrino) unlikely.
However, in May 2018, physicists of the MiniBooNE experiment reported a stronger ...
- 2,754
6
votes
1
answer
533
views
Little confusion with see-saw mechanism
Neutinos are either Dirac particles or Majorana particles but can’t be both at the same time. Then how can we write a general mass term as the sum of a Dirac mass term and a Majorana mass term? When ...
- 27.2k
5
votes
1
answer
86
views
Is the $\nu_e$ massive?
Neutrino oscillations imply that the $\nu_\tau$ is more massive than the $\nu_\mu$, and the $\nu_\mu$ is more massive than the $\nu_e$, so it's inferred that the $\nu_\mu$ and $\nu_\tau$ have mass. ...
- 18.6k
5
votes
3
answers
374
views
How are the sterile neutrinos $\nu_s$ different from the heavy right-handed fields $N_R$ (or $\nu_R$)?
To generate three light neutrino mass eigenstates via type-I seesaw, we include a set of $n$ (need not be equal to 3) heavy$^1$ right-handed fields $N_R$ in addition to three $\nu_L$ fields to the ...
- 27.2k
5
votes
2
answers
448
views
Is $N_R$ a Majorana field in the Seesaw Lagrangian?
Consider the Lagrangian for the type-I seesaw given by
$$-\mathcal{L}=\bar{\nu}_{L}m_DN_{R}+\frac{1}{2}\overline{(N_{R})^c}M_R N_{R}+\text{h.c.}.$$
$\bullet$ In this Lagrangian, what is the nature ...
- 27.2k
5
votes
4
answers
1k
views
Calculating the $\mu\rightarrow e\gamma$ decay and cancellation between diagrams
In the book “Gauge theory of elementary particles-Cheng and Li, section 13.3, the $\mu\rightarrow e\gamma$ decay amplitude is calculated in the $R_{\xi}$ gauge. Regarding this derivation, I'm stuck ...
- 27.2k
5
votes
2
answers
132
views
What are the anti-neutrino flavour oscillation formulae?
All the textbooks and references that I have come across give the neutrino 3-flavor oscillation formulae. However, the formulae for antineutrino oscillations are never given. Is it possible to derive ...
- 27.2k
5
votes
1
answer
300
views
A terminology question: What are active neutrinos and why?
The mass term for the type-I seesaw is given by $$\mathcal{L}_{mass}=-m_D\overline{\nu_L}N_R+M_R\overline{(N_R)^c}N_R+h.c.$$ where the right-chiral fields $N_R$ are electroweak singlets. Since they do ...
- 27.2k
4
votes
3
answers
1k
views
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
4
votes
1
answer
732
views
What is the meaning behind the neutrino oscillation parameter?
As far as I can tell, there are 6 parameters that describe how a neutrino oscillates: 2 mass squared differences, 3 mixing angles and another parameter I don't understand at all (delta). Thus I have ...
- 71
4
votes
1
answer
238
views
If $U$ determines the mixing between fields and $U^*$ determines the mixing between states-Why?
In this pdg review, Eq. (14.1), the mixing between the flavour neutrino fields and neutrino fields corresponding to mass eigenstates are denoted as $$\nu_{lL}=\sum\limits_{j}U_{lj}\nu_{jL}\tag{1}$$ ...
- 27.2k
4
votes
2
answers
99
views
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
4
votes
1
answer
175
views
Which experiment could resolve the neutrino mass hierarchy problem?
Neutrino oscillations are sensitive to $\Delta m^2$, but not to the absolute mass scale, therefore we have the problem of the mass hierarchy.
Which experiment could resolve this problem? Is there any ...
- 1,187
4
votes
1
answer
181
views
Is this article about the SMASH hypothesis a fair assessment?
New Scientist is gushing as usual about a new development in physics. This one, called SMASH, looks truly interesting, though.
Apparently it's a small extension to the Standard Model that explains "...
- 212
4
votes
1
answer
162
views
Matter effects contributing in solar, atmospheric and reactor neutrino oscillations
Neutrino oscillations are affected by the matter effects. For solar neutrinos, which are exclusively neutrinos of $\nu_e$ type, the matter effects can be contributed by (i) the solar plasma, (ii) ...
- 27.2k
4
votes
1
answer
521
views
Flavour symmetries of neutrino and charged lepton mass matrices
The symmetry of neutrino mass matrix $M_\nu$ is often realized as $$G^TM_\nu G=M_\nu$$ where $G$ is an element of the corresponding symmetry group. Is this because the neutrinos are Majorana in nature?...
- 27.2k
4
votes
2
answers
226
views
Neutrino Nuclei Coherent scattering and the Dark Matter lower wall
Suppose that current and new forthcoming dark matter direct detection experiments find no evidence of Dark matter events and exclude interactions of hypothetical DM particles (like LSP or similar) in ...
- 6,727
3
votes
2
answers
320
views
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
3
votes
2
answers
1k
views
Can charged leptons undergo oscillation?
Neutrino oscillation is an observed fact while charged lepton oscillation is not. Unlike neutrinos, is it possible for the charged leptons to oscillate, theoretically? In other words, is there ...
- 27.2k
3
votes
1
answer
372
views
What distinguishes the behaviour of particle from its antiparticle: C violation or CP violation?
It is said that a CP violation would mean that the behaviour of the particle is different from the behaviour of antiparticle. Why is C violation not good/enough?
- 27.2k
3
votes
1
answer
163
views
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
3
votes
2
answers
459
views
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
3
votes
1
answer
158
views
Can neutrinos change chirality by oscillating?
Active neutrinos are left-handed while sterile neutrinos are right-handed. There are speculations that active neutrinos can oscillate into sterile neutrinos. Can neutrinos change chirality by ...
- 27.2k
3
votes
2
answers
227
views
What is meant by the absolute scale of the neutrino mass?
In this review titled "Pieces of the Flavour Puzzle" the author Ferruccio Feruglio wrote in the introduction that
"The origin of the parameters in the flavour sector of the Standard Model (SM), ...
- 27.2k
3
votes
1
answer
1k
views
What is the correct definition of the Jarlskog invariant?
In this lecture on neutrino physics, Prof. Feruglio defines the Jarlskog invariant as
$$J=\text{Im}(U_{\alpha i}^{*} U_{\beta i}^{\,} U_{\alpha j}^{\,} U_{\beta j}^{*})\tag{1}$$
where $U$ is the ...
- 27.2k
3
votes
1
answer
102
views
PDG review says "The flavour of a given neutrino is Lorentz invariant."
This the starting paragraph of section 14.1 PDG review (PDF) asserts:
The flavour of a given neutrino is Lorentz invariant.
What does this really mean? A neutrino of a given flavour $\alpha$, i.e.,...
- 27.2k
3
votes
1
answer
110
views
Is there a bound on the number of sterile neutrinos from cosmological observations?
The right-handed sterile neutrinos $\nu_{R}$ are electroweak singlets. They do not contribute to the electroweak anomaly, and therefore, their number is not fixed by the requirement of the anomaly ...
- 27.2k
3
votes
1
answer
59
views
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
votes
1
answer
176
views
Lowering the type-I seesaw scale without fine-tuning
The type-I seesaw mechanism yields the effective neutrino mass $$m_\nu\sim -M_DM_N^{-1}M_D^T.$$ Here, $M_D$ is the Dirac neutrino mass coming from Yukawa coupling of the left-chiral neutrino with the ...
- 27.2k
3
votes
0
answers
32
views
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, ...
2
votes
3
answers
898
views
How is $\Delta m^2_{12}$ is identified with the solar mixing angle?
I was reading various reviews on neutrino physics but I couldn't understand the following to complete satisfaction.
How is $\theta_{12}$ identified with the Solar mixing angle and $\Delta m^2_{21}$ ...
- 27.2k
2
votes
1
answer
397
views
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
2
votes
1
answer
101
views
How does one measure anti-neutrino flavor oscillation probabilities?
The Dirac $CP$ phase $\delta_{CP}$ in the $U_{PMNS}$ mixing matrix lead to the $CP$-violation in the Lepton sector. I think this can be tested by comparing neutrino flavour oscillation probabilities ...
- 27.2k
2
votes
1
answer
1k
views
Why are the neutrino flavour eigenstates and mass eigenstates different?
Why does this happen for neutrinos and not for say, electrons and muons. Is there some way to predict which particles might oscillate amongst their flavour and which won't?
- 41
2
votes
1
answer
178
views
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
2
votes
1
answer
528
views
How can we calculate the PMNS matrix in general?
If we only introduce Dirac mass terms for neutrinos, we have analogous to the quark mass matrices, a normal $3 \times 3$ neutrino mass matrix $M_\nu$, written in the basis: $(\nu_L^1,\nu_L^2,\nu_L^3)...
- 10.3k
2
votes
1
answer
165
views
Why are the radiatively generated neutrino masses finite?
In the Zee model and the Ma model of radiative neutrino masses, a naturally small neutrino mass is generated at the one-loop level. But loop diagrams are generally divergent. There is no mass at the ...
- 27.2k