Questions tagged [weak-interaction]

one of the four known fundamental forces of nature and the one responsible for beta-decay radioactivity. The weak interaction is very short-ranged and more weakly coupled than either the strong nuclear force or electromagnetism. At energy scales above the Z mass the weak and electromagnetic interactions are unified (that is subject to a unified mathematical treatment).

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The CKM Matrix and Weak Universality

The CKM matrix was constructed first by Cabibbo in order to preserve weak universality, so that all the $SU(2)$ doublets would couple identically to the weak vector bosons. Could we have instead ...
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Current conservation in presence of SSB: weak currents

The Standard Model SSB breaks the $SU(2)_W \times U(1)_Y$ to $U(1)_{EM}$. The Noether currents associated to the unbroken group are $J_{a,\mu} = \bar{\psi} \gamma_\mu \frac{\tau_a}{2} P_L \psi $ and $...
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How is the mixing of neutrinos related to eigenstates?

Can someone please explain to me why the following statement is true: "Neutrino mixing phenomena arise from the noncoincidence of energy-propagation eigenstate and the weak (interaction) ...
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Did I get the shape of the weak interaction Lagrangian for Majorana Neutrinos right?

At first: This is the first question I ask on this forum, so please let me know if and how I can improve my style! The actual question is: Did I get the shape of the weak interaction Lagrangian for ...
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Is there any simple way to predict beta decay half lives?

Question For nuclides that decay by alpha emission, the Geiger-Nuttall law gives a simple and reasonably accurate estimate of the half-life. Essentially, one can model the alpha particle as a ...
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CPT theorem and the weak interaction

I am trying the understand how the weak interaction obeys CPT symmetry. My understanding is that, under a CPT transformation, the Lagrangian for the Standard Model should be invariant, and thus the ...
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Quark family/generation quantum numbers

Shouldn't strangeness and charm be essentially the same quantum number, the eigenvalue of the family operator for family #2 of the quarks, and similarly for top and bottom, for family #3? It appears ...
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The Higgs field and the handedness of emitted neutrinos in electron capture

Background: I was looking into how the Higgs mechanism gives electrons and other fermions a mass and to understand this was looking into the handedness of electrons and neutrinos during their ...
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Why aren't neutrino oscillations averaged out by incoherence?

Electromagnetic oscillations that have incoherent sources do not manifest any oscillatory or interference patterns. Only when the sources are distilled by appropiate filters like prisms is the ...
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Can black holes interact with the weak force? (I.e., is this a reasonable expectation?)

This question is mostly about a strange seeming similarity that I've noticed between the nature of the weak force and the nature of black holes, which seems to imply that even some astrophysical black ...
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Experimental hints for electro-weak theory

What exact observation tells us that the fields which are "eigenfields" to the weak interaction are not mass "eigenfields"?
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Mistakes in the Wikipedia figure on elementary particle interactions

There are some mistakes I think in the figure of Wikipedia on particle interactions in standard model: https://en.wikipedia.org/wiki/Mathematical_formulation_of_the_Standard_Model#...
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Do the right-chiral electron and left-chiral positron interact with the anti-$W$ boson?

I've been reading Flip Taneda's 'quantum diaries' articles, and he references the famous fact that the W boson (weak force) only interacts with left-handed electrons and right-handed positron. BUT... ...
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What was the motivation for thinking the weak interaction could be described by a Yang-Mills theory?

In some sense, describing the strong force using an $SU(3)$ Yang-Mills theory makes perfect sense: Yang-Mills theories describe massless bosons, of which the gluon is clearly a member, while the two ...
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What is the relative strength of the weak force?

When comparing the weak gauge coupling to the electromagnetic gauge coupling (fine structure constant alpha) textbooks give the value ("relative strength") 10^-5 or the value 10^-13. Why are ...
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Why does the factor $m_b$ occur in the weak effective operator $\mathcal{O}_7$?

According to [1] the dominant operators contributing to the considered decay $B \rightarrow K^{(*)} \ell^+ \ell^-$ are given by $\mathcal{O}_7$, $\mathcal{O}_9$ and $\mathcal{O}_{10}$. While I ...
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Difference between massless neutrino flavours

The title pretty much sums up the the question, what's the difference between massless neutrino flavours? I know that an electron neutrino interact with the electron and so on for the muon and the $\...
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Fundamental invariants of the electroweak sector?

In a previous question, I asked what the matrix representation of the electroweak fields is, and I was told they are identical to the Faraday tensors, but come in a set of three ($W_i, i\in \{1,2,3\}$)...
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Derivation of Thermally averaged cross sections

In many sources discussing neutrino decoupling I find the following claim: "The thermally averaged rate of weak interactions is given by: $\Gamma = n \langle\sigma |v|\rangle$, where $\langle\...
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What exactly does the weak force do?

I know that the weak force acts on nuclei and causes decay. But what exactly does the weak force do? Or to put it another way, why do we call it a force? Does it push the red particle of the picture ...
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Fermion couplings

We know that the absolute sign of Axial and Vector couplings of fermions cannot be measured. Could anyone help me understand which symmetry does this condition arise from?
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Annihilation cross-section of neutrino-antineutrino pairs [duplicate]

Presumably this should be a tiny cross-section (or not?), but presumably it should be at least qualitatively similar to the 511 keV line that clearly distinguishes electron-positron annihilation, ...
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Why are semileptonic decays of the $\Lambda$ baryon so suppressed?

Looking at the Particle Data Group tables of the $\Lambda$ baryon, I find that the rate of the hadronic decay $\Lambda \to p \pi^-$ is 64% while the semileptonic decay $\Lambda \to p e^-\nu_e$ has the ...
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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 ($M_R \gg m_D$). ...
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Electroweak field-strength tensors

The Lagrangian density for the interaction term of the bosons $W_1,W_2,W_3,B$ in the electroweak theory is $$ \mathcal{L}_g=-\frac{1}{4}\operatorname{Tr}(W^{\mu\nu}_aW_{\mu\nu}^a)-\frac{1}{4}B^{\mu\...
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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 ...
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Photon emission in Wu experiment

The Wu experiment is the first experiment to prove parity violation of the weak interaction. In the experiment, ultra-cold cobalt-60 atoms are aligned in a magnetic field. The cobalt-60 atoms decay to ...
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Sphalerons In Laymans Terms

I’m a 3rd year physics undergrad and I’ve just finished my first particle physics course. I’m looking for an explanation (at my level) of what a sphaleron is? They were mentioned as an aside in one of ...
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Can a neutrino and an antineutrino be attracted because of weak hypercharge?

I thought that neutrinos and antineutrinos had opposite weak hypercharge. So is it theoretically possible to see a neutrino and an antineutrino form a bond between one another. Could this be because ...
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Can flavor changing neutral currents occur

It says that flavor changing neutral currents are impossible. However I am just asking what would happen if a top quark emits a Z boson or a Higgs boson.
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Why is $W$ boson decay more favorable for strange quark than $Z$ decay?

As seen below, a strange quark decays into a down quark and a neutral pion. Why is the top decay more likely than the bottom decay? edit: is it because of this? https://en.wikipedia.org/wiki/Flavor-...
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How was it determined how many neutrinos result from a single Beta decay?

What experiment, if any, shows how many neutrinos are produced for the decay of one W boson?
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$W^-$ behavior in Neutron decay

Why does $W^-$ always decay into electron and anti-neutrino in neutron decay? Why doesn't the $W^-$ particle decay into quark-antiquark pair?
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In neutrino absorption, what is it really that absorbs the neutrino?

I have read a lot of questions on this site about neutrino absorption, and all of them mention that usually when a neutron transforms into a proton or vica versa, that is really an up quark transforms ...
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Do neutrino oscillations generate back-reaction in matter?

Typically all interactions generate some back-reaction. Neutrino oscillations are a subtle long-range interaction that induce weak-force interacting neutrinos to flavor-oscillate, and the properties ...
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Presenting Numbers in Particle Physics

We got some data from the OPAL-detector at CERN and were supposed to analyze the decay of the $Z^0$-particle. In order to do so, we had to write a Python-scriptum. Now, in Python, we obtained the ...
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Where does the electron come from when a free neutron transforms? [duplicate]

I'm reading in Tales of the Quantum (page 68) that "Each neutron is made up of one up quark and two down quarks. In a free neutron one of the down quarks will transform into an up quark, turning the ...
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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 ...
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Why can we only measure the electromagnetism and gravitation in real life, and not the nuclear forces?

Why can we only measure the electromagnetism and gravitation in real life, and not the nuclear forces? All our senses are explained with EM forces and pressure values directly and heat transfer.
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Pion decay reaction and the invariance of momenta

Let's take the following weak decay reaction: $$ \pi^+ → \mu^+ + \nu_\mu $$ where masses and the pion energy are known. Considering the relations among momenta of the involved particles, where ...
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Binding and exfoliation energy

This question could seem simple, but it's not clear for me. Let's say I have a $\text{MoS}_2$ bilayer, is its binding energy same with exfoliation energy? As far as I know, we can calculate binding ...
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Matrix element for the neutron decay using the exact $SU(3)$-symmetric limit

I want to calculate the electron spectrum in the decay process $n\rightarrow p~e^-~\bar\nu_e$. The matrix element should be written in the exact $SU(3)$-symmetric limit. Could you recommend any ...
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Electron beam induced electron capture?

Would it be possible to induce electron capture/fission by firing an electron beam at a heavy-element target? I know pelletrons/Van de Graff generators/accelerators can produce electrons of around ...
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Quark Chirality Constraints in Nucleons

SW Engr here educating myself on particle physics, apologies in advance for any phrasing errors. I tried the google machine to no avail. Q: If only left handed matter fermions experience the weak ...
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Glashow-Weinberg-Salam (GWS) Theory for Gauge Boson Masses

I am supposed to find the mass of the $W^\pm$ and $Z$ bosons from the following covariant derivative: $$D_\mu = \partial\mu - \frac{ig_1}{2}B^\mu -ig_2t^iW^{i\mu} $$ and from $\mathcal{L}_{kin. ...
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What are the allowed $W$ bosons in Muon decay?

I am curious about the allowed Feynman diagrams in Muon decay and whether the $W$ boson can be either the $W^+$ or $W^-$. Muon decay follows the reaction: \begin{equation} \mu^-\rightarrow e^-+\...
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Allowed Feynman diagrams for charged current weak interaction

I am reading about the charged current weak interaction. The notes I am using state that, with the charged current weak interaction, transitions across quark generations are possible, but suppressed. ...
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Are there wavelengths associated with the weak field and strong field bosons?

Are there wavelengths associated with the weak field and strong field bosons? Anyone care to share their take on this?
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Angular momentum conservation of muon decay

In the (anti-)muon decay process from the weak interaction, specifically $\mu^+ \rightarrow e^+ + \nu_e + \bar{\nu}_\mu$ how should I address the angular momentum conservation in the muon rest frame?...
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Is beta decay accelerateable? [duplicate]

Is there any way to alterate weak interaction and thus the rate of beta decay by making it slower or faster? If yes, how? Would radiating some extra bosons or neutrinos, perhaps in a focused beam, ...

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