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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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When can you simplify the W boson propagator

I have seen in several sources that the propagator of the $W$ boson is: $$\frac{- i \left( g^{\mu\nu} - \frac{P^\mu P^\nu}{m_W^2} \right)}{p^2 - m_W^2} $$ But then in some calculations (usually ...
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What would a universe with a long range weak force look like?

If the W's and Z bosons were massless at low energies (i.e. no Higgs interaction), what would the universe look like? Would there be "weak bound states" ? How would electromagnetic theory differ with ...
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Left Handed / Right Handed Particles and the Weak Force

Good Afternoon, I am a 50-year-old guy who was never a scientist or physics student. Just a person who loves to read books on particle physics. I have a question on the Weak Force and particles. (...
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Muon neutrino interacting with nucleon's quarks

I'm considering the muon neutrino/anti-quark interaction with the nucleons of ice in the IceCube experiment. The purpose is to decide which antiquarks are $\bar{q}$ and $\bar{q}'$. I have the ...
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Muon neutrino and down quark interaction diagram

My questions concerns the IceCube experiment, in particular, the interaction between muon neutrino and the down quark. I've drawn the following Feynman diagrams: Are both diagrams correct? Can I say ...
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Unitarity violation: sign inconsistency in Quigg

In Gauge Theories of the Strong, Weak, and Electromagnetic Interactions, C. Quigg explains how the process $\nu \overline{\nu} \rightarrow W^+ W^-$ violates unitarity at high energy unless we add the $...
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Constraints on RH component of fermion triplet under $SU(2)_L$

Consider a fermion $\chi$ whose left-handed part is in a triplet representation of $SU(2)_L$: $$ \chi_{L} = (\chi^1,\chi^2,\chi^3)_L^{\ \ \text{T}}. $$ The charged current of $\chi_L$ (i.e. its ...
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Charged and neutral current in Feynman diagrams

I am stuck on finding the 'right' mediator in weak interactions. Consider the following reactions. 1: $$\mu^+\rightarrow \bar{\nu}_\mu + e^+ +\nu_e$$ This is mediated by the vector boson $W^+$. 2: ...
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weak interaction and Parity violation

It is said that the Weak Interaction only couples to left-handed particles which a negative spin (left-handed). However some sources say that spin or helicity is dependent on the observer's position ...
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Energy difference between enantiomers (matter/antimatter)

I am aware of the fact that enantiomers have different energies, for example L-amino acids have different energy than D-amino acids. The difference is not significant and is most usually about $10^{-...
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Muon decay - Type of interaction

Why does weak interaction occur when a muon decays? Why can't electromagnetic interaction occur when a muon decays?
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Does the weak force obey the CPT symmetry? How?

I have read that the weak force does not obey the charge symmetry, the parity symmetry, and the time reversal symmetry. Then how does it obey the CPT symmetry?
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Why is the muon decay a Flavor Changing Charged Current (FCCC) process?

One way of understanding why the muon decay $$\mu^-\to e^-+\bar{\nu}_e+\nu_\mu\tag{1}$$ is a Charged Current (CC) process is to write the intermediate step through which the decay (1) proceeds i.e., $$...
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What happens during a weak interaction?

For e.g. during $\beta^-$ decay a $W^- $ boson is emitted changing an up quark to a down quark. This seems very weird to me as it looks like that up quark is not interacting with some other particle ...
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What are the other components of the weak isospin?

Sorry for a lazy question, I was just looking this up on the internet for a basic grasp of Standard Model. However, I couldn’t find anything on Wikipedia or just somehow managed to miss it on my ...
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Why Majorana neutrinos is a solution for the existence of only LH neutrinos?

At lesson my teacher stated that the possible reason for why only LH neutrinos are observed are that either: neutrinos are Dirac fermion but the RH neutrinos are not interacting weakly or that they ...
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Why does the weak nuclear interaction have a shorter range than strong nuclear interaction?

My textbook says: "Weak nuclear interaction acts on protons, neutrons, electrons and neutrinos in order to bring about beta decay. It has very short range (10-18m)" "Strong nuclear interaction ...
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Half-life of $W$ and $Z$ bosons

$W$ and $Z$ bosons should decay through weak interaction. But their half-life is around $\tau = 10^{-25} s$ which is a typical value for particles decaying through strong force (instead of a $10^{-12}-...
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Could anyone explain how energy and momentum are conserved when an isolated neutron decays into a beta-minus particle?

I am not able to get to a reasonable explanation as to how momentum and energy are conserved when an electron, a proton, and a neutrino are created.
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Rule of thumb for identifying dominant quark contribution in loop calculations

I am trying to understand some calculations of $B$ meson decays and just stumbled upon the low energy effective weak Hamiltonian describing $\Delta S = 1$ $B$ decays: $$\mathcal{H}_\text{eff} = \...
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Antimatter: weak and strong forces

Antimatter is known to have equal mass to matter and opposite charge sign. Positron has the same mass as electron and opposite sign of charge, anti-proton has the same mass as proton and opposite sign ...
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A place of space-time where the only fundamental interaction will be the gravitational forces: does make sense?

We know that there are four (fundamental forces) fundamental interactions of nature, this Wikipedia. I'm curious about if we can speculate that there exists a place of the space-time in which, after ...
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About the electroweak force

So, I'm struggling to understand how the electromagnetic and the weak force were connected. Separately, I know pretty much how the two forces work and interact with the environment. I read a few about,...
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Universality of the Z interactions

In the SM the interaction of leptons and quarks with the Z boson are universal, and the way to see it is to start with the covariant derivatives which lead to terms of the form $$ \delta_{ij}\bar{\psi}...
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Equality of positron and proton charge problem statement

When I hear that the equality of positron and proton charge is an unsolved problem I assume that we are putting the electric charge by hand in the electroweak section of the SM Lagrangian. Is this ...
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Could the electron count as a force-carrying particle?

Pretty straight-forward this one. If we're going to get a bit more nit-picky about this relatively straight-forward question I'd like to first of all point out that yes, I have considered that ...
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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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Measuring characteristic time of strong and weak interaction using cross section

Consider a scattering between two particles a and b that produces two particles c and d: d is stable, while c decays in two other different particles e and f. The first interaction is by strong ...
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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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Parity in Madame Wu experiment

To see the effects of parity violation it's necessary to consider an observable that is non-invariant under parity, was chosen the projection of the electron momentum ($p_e$) on the polarization ...
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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?