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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Electroweak Force Capabilities

I understand that Electroweak force is the unification of Weak force and electromagnetism, but that are the actual effects or capabilities of this fundamental force? or at the very lease, what are the ...
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Neutral Kaon Decays to positively/negatively charged Pions

$K^{0}$ meson consists of a $d$ quark and an $\bar{s}$ antiquark. Its antiparticle $\bar{K^{0}}$ consists of an $s$ quark and a $d$ antidown quark. $$|K^{0}\rangle=|d\bar{s}\rangle$$ $$|\bar{K}^{0}\...
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Feynman amplitude and tensor 4-vector multiplication (muon neutrino-electron scattering)

In the calculation of the Feynman Amplitude for the muon neutrino-electron scattering (in the Charged Current way from W boson), or $e + \nu_\mu \rightarrow \nu_e + \mu$ (considering the 4-momentum ...
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What gives mass to dark matter particles?

Assuming that dark matter is not made of WIMPs (weakly interacting massive particles), but interacts only gravitationally, what would be the possible mechanism giving mass to dark matter particles? If ...
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Well colour me surprised$.$

I was reading Scharf's Quantum Gauge Theories: A True Ghost Story when I stumbled upon the following paragraph (p. 118): The standard example of a gauge theory with massless gauge fields is the ...
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Weak interaction of $(\nu^c)_R$ fields of the SM and $N_R$ fields in type-I seesaw extension of the SM

The antiparticle of $\nu_L$ is given by its charge conjugated field i.e., $(\nu_L)^c$ which is equal to $(\nu^c)_R$. Both $\nu_L$ and $(\nu^c)_R$ are part of the Standard Model (SM) of massless ...
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A proton's weak charge is .0719. Is this dimensionless? A ratio?

A recent piece of major news in the physics world is that the proton's weak-force charge was measured to be .0719. Is that a ratio? A dimensionless number, with no units? The articles I read ...
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Is it at least theoretically possible for an electron and an antimuon or antitauon to annihilate?

In other words, can mismatched particles and antiparticles react with each other? What about an up quark and anti-down quark?
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Is it possible for the reaction $\pi^+ \, \pi^- \rightarrow \nu_e \, \bar{\nu}_e$ to occur? If so, how would this happen?

The reaction doesn't violate any conservation laws that came to my mind - however I am having trouble thinking of how it might occur.
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How are neutrino energy eigenstates different to the momentum eigenstates?

Neutrino flavour eigenstates can be expressed (approximately) in terms of their mass eigenstates, leading to neutrino oscillations. $|\nu_e\rangle = \cos \theta |\nu_1\rangle - \sin \theta |\nu_2\...
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How to derive the decay rate from the Lagrangian of an interaction?

For instance, in Fermi theory of beta decay, the lagrangian is shown in the fig. How do we derive the decay rate and the distribution of kinetic energy from that?
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Question about nuclear reation

In Landau and Liftshitz Volume 5 page 318, it talks about nuclear reaction in high density, where proton reacts with electron and becomes neutron and neutrino: $$A_z+e^- = A_{Z-1}+\nu$$ where $A_z$ ...
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No global monopoles in QCD

If a global symmetry gets both spontaneously and explicitly broken, the explicit symmetry breaking pattern is crucial for understanding the formation of topological defects. For example, in the axion ...
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Why is the Beta-Decay of a Neutron asymmetric?

The Wu-experiment, which originally showed the parity violation of Beta-Decay experimentally, is often used to give an intuitive explanation for the asymmetry of the decay: $${}^{60}_{27}\text{Co} \...
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What is the reason for emission of anti-neutrino during beta emission?

My book says that "Later on, to keep the number of particles either odd or even on both sides another particle called anti neutrino, was also assumed to be emitted along with the beta particle. ...
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Does the field (force-carrying) of a gluon or boson have a magnetic-like shape? Not spherical

The challenge of force-carrying boson is that many experiments generate results that are not consistent. Hence, quantum statistics. It is established that things like 'strong nuclear interaction/...
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Why is the Fermi coupling $G_F$ is measured from muon decay?

The decay rate of all weak processes, calculated from the $V$-$A$ theory will contain a factor of $G_F$, the Fermi coupling constant. However, $G_F$ is usually measured from $\mu^-$ decay which is in ...
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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.
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Corrections from violation of P-symmetry for chemistry, biochemistry, life?

Imagine a mirror image of a biological cell: all molecules replaced with their symmetric versions (enantiomers). At least in theory, we should be able to synthesize it (Wikipedia), for example for ...
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Weak isospin 1/2 vector bosons

The weak vector bosons are spacetime vectors (spin 1) and also incidentally weak isospin vector components (-1, 0, +1). I understand why that is required from nucleon beta decay and other weak ...
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Calculation of the weak coupling constant

There are two ways to calculate the coupling constant of the weak interaction $g$. 1) From the electromagnetic coupling constant and the weak mixing angle, using the relation $${\sf e} = g\sin(\...
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What is the direction of the weak force between electrons and protons?

Is the weak force between electrons and protons repulsive or attractive? Does it affect somehow the electron shells of atoms?
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Why can increasing energy, the weak force and the EM-force become a similar force?

When the heat of the universe was much higher it seems that the weak force and the EM-force was combined into the electro weak force. For a layman the EM-force and the weak force look quite different,...
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If Baryons are subject to the strong nuclear force, how are they involved in Beta decay?

The question is really in the title with this one, I just need a little bit of clarity, consider beta-minus decay, which is an interaction governed by the weak nuclear force, $$n\to p^+ +e^- +\bar v_e$...
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Should some neutral particle electromagnetic decays also involve the weak force?

Take, for example, the neutral pion, π0. 98.823% of the time, it decays electromagnetically, into two photons: π0 → 2γ On its face, this process does not violate any flavor quantum numbers: the ...
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Why is $|\bar{K}^0\rangle=\mathscr{CP}|K^0\rangle$ and not $|\bar{K}^0\rangle=\mathscr{C}|K^0\rangle$?

If the charge conjugation operator $\mathscr{C}$ changes a particle state into the corresponding anti-particle state then we must write $|\bar{K}^0\rangle=\mathscr{C}|K^0\rangle$. But instead, we ...
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Is the weak force conservative?

Does it make sense to talk about "conservative" potentials and forces in (quantum) field theory? If yes, to what extent? Is (for example) the weak force conservative and what would it mean ...
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Why doesn't the Higgs give mass to neutrino? [duplicate]

We learn that elementary particles acquire mass through the weak interactions with the Higgs field. The photon and gluons do not interact weakly, do not coupe with the Higgs field and for this reason ...
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Dark matter mass and weak interactions

If dark matter forms halos around galaxies, it must have invariant mass. In the Standard Model, elementary particles acquire mass usually through the weak interactions with the Higgs field. Does this ...
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Why are the masses $m_{W}/m_{Z}$ and the coupling constants $e/g$ related in electroweak unification?

Gottfried and Weisskopf write in their book, in the chapter on electroweak theory, that $\frac{m_W}{m_Z} + \left(\frac{e}{g}\right)^2 = 1$ In this expression, $m_W$ and $m_Z$ are the masses of the $...
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Conservation of Strangeness

The above image is considered to be a reaction that can occur practically. However, isn't the strangeness of $\Xi^-$ -2, and $\Lambda^0$ -1? This would leave a net -1 value on the left side of the ...
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Can neutrinos “hit” electrons?

I understand that particles interact via the fundamentals forces of nature. For example photons interact with matter because they carry the change in the electromagnetic field. Neutrinos, on the other ...
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What does happen to electrons in the weak force decay?

What happen with the Electrons produced in Stars due to the weak force decay? Do they combine with other atoms? Are they just pushed out of the Sun? Do they help with the electron degenerative ...
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Why do weak interactions exclude gluons?

Weak interactions seem the most universal after gravitation. A very few particles avoid them, only the photon and gluon, plus right leptons. The photon, however, is a part of the electroweak ...
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Why are $c_V$ are $c_A$ in the four-Fermi Lagrangian left unspecified?

The four-Fermi interaction in the form\begin{equation} \mathcal{L}_{int}=-\frac{G_F}{\sqrt{2}}[\overline{\psi}_{(e)}\gamma^\mu(c_V-c_A\gamma_5)\psi_{(e)})][\overline{\psi}_{(\nu)}\gamma_\mu(1-\gamma_5)...
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Why $\nu_ee^-$ has a larger scattering cross-section than $\nu_\mu e^-$ cross-section?

Why is the scattering cross-section of $\nu_\mu$'s with the electron $e^-$ much smaller than the scattering cross-section of $\nu_ee^-$ scattering both of which take place through charged current weak ...
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Does weak interaction always come in decays?

Well, essentially I'm confused about how weak nuclear force works. Decay is usually mentioned in studying weak nuclear force, so does weak force always work in decays? If so, is all decay is based on ...
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Orbital angular momentum in weak interaction

I am bit confused with a statement in Griffiths where he talks about the decay of pions by weak interaction to muons and neutrino. Here, he says that if angular momentum of muon and neutrino is ...
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Has the weak force ever been measured as a force?

Gravitational and electrostatic forces are everyday phenomenon, and continue to be tested by sophisticated experiments at various distances. Rutherford measured the electrostatic repulsion of alpha ...
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Manifestation of chirality in particle physics

I understand (I hope) the meaning of chirality but I am not really sure how does it affects the weak interaction. From what I understand, an electron is a superposition of left and right chirality ...
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Are electroweak particles stable?

Photons that [are associated with] the electromagnetic force are stable; while the W and Z bosons that [are associated with] the weak force are short lived. I guess that the high temperate electroweak ...
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How to integrate out the W-boson fields?

What does it mathematically mean to 'integrate out' the W-boson fields to obtain the Fermi Lagrangian from the electroweak theory? How does one achieve this mathematically? It will be helpful if ...
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Can we observe “classical waves” produced by the weak and strong nuclear force bosons?

A real photon is wieved as an electromagnetic wave. In addition, if gravitons exist, we can view real gravitons as gravitational waves. However, can we observe the waves from the weak and strong ...
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Can particles become entangled by every of the three basic forces, or even by gravity?

A pair of particles can become entangled after having had an e.m interaction. Almost every example of entanglement is that of electrons whose spins become entangled having had an e.m. interaction, or ...
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What happens when we constantly observe a neutron?

The mechanism which we think neutrons decay is by the weak force. The interaction between the quarks of a neutron cause one of them to change their flavor to "up". Thus the neutron decays into a ...
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Neutral D meson decay widths from dimensional analysis of feynman vertices

I know the decay width of a process is proportional to the interaction strengths at the vertices, and for a $D^0\to \pi^+\pi^-$ where $D^0=\bar{u}c, ~ \pi^+=u\bar{d}, ~\pi^-=u\bar{d}$, the decay ...
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Neutral vector boson from renormalizing IVB (intermediate vector boson) theory?

Consider the intermediate vector boson (IVB) theory, with the interaction Lagrangian density $$\mathcal L_I = \sum_l g_W (\overline{\psi}_{\nu_l} \gamma^\alpha(1- \gamma_5)\psi_l ) W_\alpha^\dagger + \...
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Cold neutron radiative capture by proton

What is the mechanism of cold neutron radiative capture by proton? I have seen some experimental papers on studies of parity violation via this reaction, but I haven't seen a fundamental description ...
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Why can the $W^{+/-}$ particles change quarks of different generations, while the $Z^0$ only changes leptons of one generation?

A $W^{+/-}$ particle can change a quark from one generation into a quark of a different generation, as long as these quarks (obviously) differ 1 or -1 in electric charge. So an up quark ($+\frac 2 3$) ...
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W vertex factor in weak interaction

I am puzzled by the $W^{\pm}$ vertex factor in weak interactions. In Griffiths' textbook "Introduction to Elementary Particles", the $W^{\pm}$ vertex factor is given by (10.92) on page 324: \begin{...