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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Measuring conserved charges of gauge bosons with conserved charge operators

In QED we dont care about this because the photons carry no charge and so it is no problem that the conserved charge operator: $$Q=\int\psi^{\dagger}\psi d^{3}x$$ That ends up consisting of number ...
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How does the parity eigenvalue change in cobalt-60 beta decay parity violating process?

All the explanations for why the beta decay of cobalt 60 seem to revolve around 'in a mirror flipped world the process is different', and while I understand the intrinsic relationship between ...
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Fermi's guess at the Beta Decay Hamiltonian

Just started on Walter Greiner and Berndt Müller's book on the Weak Interaction. He says that Fermi guessed the Hamiltonian for Beta Decay to be: $$ H_F = H_n^0 + H_p^0 + H_e^0 + H_\nu^0 + \underbrace{...
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Flavor changing weak neutral current and $Z^0$ boson

In Peskin QFT p.725, it says: The $K^0$ meson could decay by $Z^0$ exchange if this boson coupled to a flavor changing weak neutral current. However, $Z^0$ boson does not couple to a flavor ...
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Why $W^+$ and $W^-$ bosons counted as two types of particles? but not $e^+$ and $e^-$?

The $W^+$ and $W^-$ bosons have either a positive or negative electric charge of 1 elementary charge and are each other's antiparticles. In this sense, if we know the properties of $W^+$, we should ...
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Strong and Weak Interactions [closed]

How do I determine whether an interactions is strong or weak if what i've been given is just the particles and the type of reaction: Determine whether the following are strong or weak interactions? a ...
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How does the standard model of physics explain gamma radiation?

How can the standard model be used to explain gamma radiation? Maybe I should say how does the theory of quarks, weak force, and strong force combine to explain gamma ray emission during a decay ...
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Flavor-changing neutral current in the technicolor

What is the issue/problem of Flavor-changing neutral current in the technicolor model stated in this lecture by Nima Arkani-Hamed? Why the technicolor model produces Flavor-changing neutral current (...
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Do physicists understand what causes nuclei to decay?

I know that it decays due to instability but do physicists understand what exactly leads to decay. I know about $Z$ and $W$ bosons but I mean before this occurs. What happens in the nucleus for a $Z$ ...
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Convention for the Weak interaction matrix elements

In the book from Quigg (Gauge Theories of the Strong, Weak, and Electromagnetic Interactions), it is said at the beginning of chapter 6 ( in order to derive the matrix element of weak interaction at ...
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Derivation of interaction potentials of fundamental forces

In Gauge theory of weak interactions by Greiner and Müller, they show the following superb comparison of the interaction potentials between particles as a function of separation: I have never seen ...
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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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Can we infer from weak isospin symmetry the existence of sub-quark particles?

In the old theory of the strong force, where the strong force was thought to be conveyed by massive mesons (pions), as one can read here: The discovery of the neutron in 1932 revealed that atomic ...
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Asymmetry in left-right-handed electron production

I’m studying the weak interaction and there is a part about the asymmetry in left-right-handed electron production that got me confused. Specifically the author of the book I’m reading presents the ...
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Has there been research done on the dependence of particle decay to its immediate surroundings?

The meson particle, Kaon, can decay into pions or leptons + neutrinos. Each decay has its own probabilities as measured and confirmed during experiments. Has there been any research into the ...
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Do electrons interact attractively?

I read that electrons could interact attractively in superconductors and form Cooper pairs. This attraction is due to the electron–phonon interaction, with the phonon being the collective motion of ...
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Can Z bosons mediate short-range forces between electrons?

The flavor quantum numbers and charge of Z bosons should allow it to mediate between electrons without violating any conservation rules. So at very short displacement scales do electrons actually ...
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Everyday repercussions of nuclear forces change

I'm pretty sure that, if all of a sudden gravity just disappeared (someone just set $G=0$ by turning a magical knob) we would notice immediately, starting to float in the air and a bunch of other ...
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What determines whether free neutron decay results in the production of a neutral hydrogen atom?

Free neutrons (outside the nucleus) are known to be highly unstable with a mean lifetime of around 14 minutes and 40 seconds. Inside the neutron, which is composed of 1 up quark and 2 down quarks, a ...
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(In a beta decay) Between what particles are W bosons exchanged?

According to what I've learned, when two electrons repel each other, photons are exchanged between the electrons, and gluons are exchanged between quarks in a nucleus. However, in beta decay, it seems ...
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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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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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