Questions tagged [neutrinos]

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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Dirac equation for neutrinos

Neutrinos are described by spinors. But they don't have a defined mass (they are in a superposition). How can I write the Dirac (Majorana) equation for neutrinos? Maybe $$i \gamma^{\mu} \partial_{\mu} ...
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Why did particle physicists believe the neutrino was massless, according to their Standard Model?

The Higgs field that gives (some) particles mass was theorized to solve problem(s) with the weak force; the neutrino only interacts with the weak force, so.... Also, it is a fermion, these otherwise ...
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Neutrino temperature

I was wondering if anybody knows the relation between the photon temperature $T$ and neutrino temperature $T_{\nu}$? And why this can be written as $$T_{\nu}=\left(\frac{4}{11}\right)^{1 / 3} T \...
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Hermitian conjugate of Majorana mass term

I've been reading up on neutrino physics (in particular the seesaw mechanism) and have seen something like this written for the Majorana mass term of a lepton (see, eg: here): $\overline{(\psi_{L})^{c}...
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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 ...
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Review of experiment $g-2$ of the muon

This week a new development was announced to measure the pressure of the muon magnetic moment and the variation of its result on the theoretical value. The question is: what is the meaning of this ...
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Finding neutrino's spin from beta-decay

Since in a beta decay $n \rightarrow p+e^-+\overline\nu$ total angular momentum must be conserved $\frac{1}{2}=s_p \oplus s_e \oplus s_\nu \oplus L$ it follows that for $L=0$ neutrino's spin is either ...
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What happens in Neutrino-antineutrino annihilation? [duplicate]

They only interact with gravity and weak force, so how do they emit their energy? My theory is that they would somehow emit photons (?)
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Will a neutrino gas always stay at the same temperature?

Does the neutrino gas pervading the universe always have the same temperature? Does it still have the temperature as the neutrino gas that emerged from the big bang? Neutrinos don't interact, so how ...
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Computing flux and energy density of IC191001A event

In 2019, IceCube Observatory has detected a >100 TeV neutrino called IC191001A. Let's assume that its energy is exactly 100 TeV and the effective volume of IceCube is exactly 1 km^3. What was the ...
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What is the acceleration rate of a neutrino? [closed]

I understand that photons do not have acceleration because they are massless. But what about neutrinos, which have been proven to have mass due to oscillation? Let's assume a typical Solar neutrino ...
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I need a kilogram of neutrinos. What are the challenges?

So I am a benevolent genius that figured out that if only I had a kilo of neutrinos in a bottle, I could solve some long standing problems (climate change, rockets landing upright, world peace, the ...
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Neutrino appearance and disappearance experiments

Why in neutrinos appearance experiments the background is said to be small? and how is it connected to the mixing angles? Why is it opposite in the neutrino disappearance experiments?
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What is the mechanism of the Askaryan effect?

(Quoted largely from Wikipedia): Askaryan radiation, known otherwise as the Askaryan effect, is a phenomenon which occurs when a particle traveling faster than the phase velocity of light in a dense ...
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How many neutrinos would it take to kill you?

Of course, there are many different kinds, so let's assume: they'rre all standard $v_e$. they all intersect your body in random places. they are going at say, 10% of c (about accelerator speed). ...
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Are neutrinos and anti-neutrinos the same thing? [duplicate]

Neutrinos are subatomic particles with no electrical charge. Anti-matter has the same mass, spin, etc. as that of regular matter except the charge of anti-matter is opposite to that of the normal ...
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Who predicted the existence of the muon neutrino?

The Wikipedia article on the muon neutrino says: The muon neutrino is a lepton, an elementary subatomic particle which has the symbol $\nu_\mu$ and no net electric charge. Together with the muon it ...
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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 ...
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Why is the conservation of lepton number a thing?

Since there is no way to tell neutrinos and antineutrinos apart, does conservation of lepton number make any sense? As far as we can tell, the neutrinos and antineutrinos are indistinguishable so from ...
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Photon - Neutrino interaction

Suppose we have a laser source, that means a coherent laser beam formed by 'in phase' photons. Is it possible to calculate how many photons can change their wavelength in neutrino - photon interaction ...
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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) ...
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How do you relate the number densities of neutrinos and photons soon after the positron–electron annihilation?

I found this equation: $n_\nu = \frac{3}{4} \frac{g_\nu T_\nu^3}{g_\gamma T_\gamma^3} n_\gamma$ Where does it come from?
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Why was a third particle, the neutrino, necessary to explain the continuous energy spectrum of beta-decay? [duplicate]

Question pretty much in title. I am confused as to why it couldn't just be that the energy is shared between the 'leftover' particle and the beta particle hence creating a continuous energy spectrum ...
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Do neutrino really decay?

It is suggested that neutrino decay in both Dirac as well as Majorana models,in the former the byproduct is undetectable whatever that may mean and in the latter it is anti particle. Which is correct?
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Summing of neutrino spins in Muon decay

This might be a silly question, but I am just a beginner so please bear with me. When we average the matrix element over spins, do we also have to sum over neutrino spins since neutrinos are only Left-...
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If you travel faster than a neutrino, will it appear right-handed?

Since neutrinos have mass they move slower than lightspeed. So it is possible to move faster. And if you move faster than the relative direction of the neutrino velocity is backwards. But the spin ...
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Why is the spectrometer so big in KATRIN experiment?

I've been studying KATRIN experiment for a popularizing science project and I was wondering, why is the spectrometer so big ? I mean the thing is so huge that they had to carry it over 8000km on the ...
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Zee QFT book on the neutrino mass

in p.102 of Zee QFT book, "As of this writing, it is not known whether the neutrino mass is Dirac or Majorana. We will see in chapter VII.7 that a Majorana mass for the neutrino arises naturally ...
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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_{...
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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 ...
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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 ...
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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 ...
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Liquid Scintillator Neutrino Detector (LSND) anomaly and implication

The Liquid Scintillator Neutrino Detector (LSND) was a scintillation counter at Los Alamos National Laboratory that measured the number of neutrinos being produced by an accelerator neutrino source. ...
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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,...
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Statistical argument for n/p ratio in relativistic neutrino environment?

Consider a system with high-energy neutrinos (higher than rest mass energies of protons & neutrons) where the energy of a neutrino is specified as $E = p + sB$, $p$ being the magnitude of the ...
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Can neutrinos orbit galaxy centre like stars do?

I am layman in particle physics. I saw this question about gravitation affecting neutrinos. There is link to an article, but it is too difficult for me. Is it known if and where can neutrinos orbit ...
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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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Can someone describe in detail (or in as much detail as possible) what neutrino physicists do?

I'm a first-year graduate student; due to a series of unfortunate events I will most likely begin research in the spring (meaning I'll officially join a group and be on track for a research ...
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Detector acceptance and effective area of a neutrino detector

In many papers about neutrino telescopes I saw the term 'effective area' and 'detector acceptance'. But those were often not defined in the papers, which suggest such definitions should be found in ...
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Visualization of photon or neutrino paths as masses around them collapse into singularity

There exist a few astronomy images (https://en.wikipedia.org/wiki/Gravitational_lens#Gallery) and digital renders (e.g. https://www.youtube.com/watch?v=FIiwGa2l9X4) of strong gravitational lensing ...
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Is PMNS neutrino mixing allowed in the standard model?

Some people say that the standard model does not allow for non-zero neutrino masses: it prevents renormalization, they say. Other people say that massive neutrinos with PMNS mixing are allowed in the ...
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Derivation of matter potential from QFT

I'm trying to derive the matter potential as experienced by neutrinos from QFT. The paper I am looking at is unfortunately not publicly available online (https://doi.org/10.1103/PhysRevD.40.259) and ...
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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 ...
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Neutrinos detection. What mechanism for their interaction with matter?

As for the title, by which way neutrinos can interact with matter such as, e.g., pseudocumene or other scintillators? Is it a merely mechanical collision? Do neutrinos collide with nuclei and how &...
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Does the Electric Field Instantaneously vanish during an Electron Capture?

When an Electron Capture occurs a Neutron and a Neutrino are formed. Prior to this process due to the presence of the proton and electron an electric field must've existed however as soon as this ...
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Positron decay direction from muon

I read that in the rest frame of a positive muon, decay positrons are preferentially emitted in the direction of the muon spin. Why is that the case? The decay is $\mu^+\to e^+\nu_e\bar{\nu_\mu}$. ...
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Confused about SM neutrinos

I am a bit confused about neutrinos in the standard model. The vertex of the weak interaction charged current, implies that any neutrino interacting through the charged current must be left handed. ...
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Finding neutrino mass eigenstates from Lagrangian?

I was given this homework assignment. We have a Lagrangian density for left- and right-handed spinors: $$\mathcal{L} = i\nu_L^\dagger\bar{\sigma}^\mu\partial_\mu\nu_L + i\nu_R^\dagger\sigma^\mu\...
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Does spin direction of massless fermions require anti-particles?

If neutrinos were massless (which of course they are not), they would come in two types. The left-handed neutrino and the right-handed anti-neutrino. Therefor to get an "up" state $|\uparrow\...
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What is neutrino pair exchange? Can neutrino pair exchange deduce stronger-than-electromagnetic attractive forces between electrons?

I read recently about neutrino pair exchange. What is neutrino pair exchange? Can this exchange induce forces stronger than electromagnetic forces between electrons which in turn form attractive ...

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