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 ...

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63 views

Difference between weak and strong interactions?

This was a statement given in my class: "Strangeness is conserved in the strong and electromagnetic interactions, but not in a weak interaction " But could someone please tell me how we ...
3
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1answer
59 views

How can a left-handed fermion field create a right-handed antifermion?

My question - which is likely stupid or appears due to some confusion - stems from the following considerations: when quantizing canonically we are told (see any book on QFT) that a Dirac fermion ...
3
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1answer
107 views

What is the parity of a $W^{-}$ boson?

What is the parity eigenvalue of the $W^{\pm}$ boson, or is it even an eigenstate? I have not found any source that discusses this. I have seen some lists of particles with their parity eigenvalues, ...
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0answers
25 views

How does the weak force between two neutrinos compare with their gravitational interaction?

In short, are there cases where the weak interaction between two neutrinos is actually smaller, in (absolute) magnitude, than their gravitational interaction? There is no principle that forbids this. ...
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1answer
66 views

Weak interaction and Neutrino

I have heard that Neutrino is the only particle affected by the Weak Interaction. How is a Neutrino affected by Weak interaction? I would like to ask the detail. Are there any relationships between ...
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0answers
114 views

Fermi theory of beta decay

What are the facts that one should consider and incorporate in going from non-relativistic Fermi theory of beta decay to its relativistic generalization? In other words, how would the Lagrangian or ...
6
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0answers
96 views

Are there analogs to resistance, inductance, capacitance, and memristance connecting the weak force to electromagnetism?

A question was asked over at EE.SE recently which I tried to answer, but much of my answer was speculative. I'm hoping someone here can help my ignorance. In electronics design, there are four ...
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3answers
81 views

Exchange Particle between an Electron Neutrino and Neutron?

How can a neutrino turn a neutron into a proton? This is the equation, $$ \nu_e + n \to p + e^- \,.$$ If you draw the Feynnmann Diagram which I attempted here, "Diagram" there isn't an exchange that ...
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0answers
23 views

What were the immediate consequences Yang-Lee work on Weak Interaction?

I am studying the history of Modern Physics and Yang-Lee earned their Nobel the next year after the Cobalt experiments. I am familiar with the chronology, but am not clear what those findings meant to ...
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1answer
233 views

Can the weak force create a bound state?

My understanding is that the exchange of Z bosons could yield an attractive or repulsive "force" between two fermions. For most combinations the electromagnetic or strong interactions will take place. ...
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0answers
48 views

The difference between Z boson couplings for quarks and antiquarks

I am trying to work out the difference between Z boson couplings for quarks and antiquarks. I know that for quarks the Z has the following couplings: $Z_u^- = \frac{1}{\cos \theta_w}(0.5 - ...
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1answer
59 views

Allowed interactions for the neutral weak vector boson

Just wanted to double check a couple of things for my own sanity! I am looking at scattering amplitudes for 2 partons going to two partons with the emission of a Z boson (eventually decaying to e+ ...
4
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1answer
76 views

How do we know that weak isospin is an exact symmetry while strong isospin is not?

It is said in textbooks that if the $SU(2)_f$ or $SU(3)_f$ flavor symmetry were exact for sstrong isospin, then all members of the multiplets would be exactly equally massive. By looking at quark ...
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2answers
1k views

Weak force: attractive or repulsive?

We are always told that there are the four fundamental forces or interactions of nature: gravitation, electromagnetism, and the weak and strong forces. We know that gravitation is attractive, that ...
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1answer
158 views

What is weak interaction? I need easy and short answer

What is weak interaction? I need easy and short answer. I can't understand the definition of weak force. Why is it so difficult? Bosons, Mesons, Fermions, parity etc. Why the fundamental force is ...
4
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1answer
156 views

Why does the pion half-life differ between the charged and uncharged species?

Why does the uncharged pion have much shorter half-life than the charged pion despite the fact that the uncharged pion has a little bit less mass than the charged one, so that according to the ...
3
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1answer
194 views

Weak interaction and the Chirality of anti-particles

Consider a weak current of the form $ J^{\mu} = \bar{u}_{\nu}\gamma^{\mu}(1-\gamma^5)u_{e} $ This describes the part of a weak process where a left-handed electron converts into a left-handed ...
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0answers
55 views

Weak decays classification

Sir, We often read about Cabibbo Favourite, Singly Cabibbo Suppressed and Doubly Cabibbo Suppressed decays. I have two questions: I understand that the suppressed decays are rarer but why are ...
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47 views

chirality oscillations in weak interaction

As far as I have understood, the mass $m$ of a fermion causes a coupling of the both chiralities $\psi_L$ and $\psi_R$. This coupling would induce an oscillation of the chirality within a time scale ...
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1answer
151 views

Why neutrons in nucleus don't decay?

In this question it is explained that neutrons in nucleus don't decay because the next state would not be lower in energy than the previous. How come neutrons in a nucleus don't decay? But it ...
2
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0answers
186 views

Charged pion decay and spin conservation

Charged pions $\pi^\pm$ decay via an intermediate $W$ to (e.g.) a lepton-neutrino pair. The pions being scalar (spin-0) particles and the intermediate $W$ having spin 1, how is spin conserved in ...
4
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1answer
353 views

What is the formal definition of spin-independent vs. spin-dependent scattering?

In the search for WIMPs as the dark matter particle, there is an important distinction between spin-independent and spin-dependent scattering. Roughly, WIMPs scattering from nucleons through a ...
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1answer
242 views

Why strong and weak forces are short range? [closed]

Why are the strong and weak nuclear forces short range? Are quarks confined or welded together? Why are elementary particles confined at short range? Or is color confinement color welding? the ...
11
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3answers
683 views

What stabilizes neutorns against beta decay in a neutron star?

Free neutrons are known to undergo beta decay with a half-life of slightly above 10 minutes. Binding with other nucleons stabilizes the neutrons in an atomic nucleus, but only if the fraction of ...
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0answers
22 views

Some basic questions about electric field & nucleus [duplicate]

I am not good in physics.You can say I am beginner in this field. I have some basic questions. I ju st want to know that [1] If there is repulsive force between same charges proton-proton then why ...
3
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1answer
316 views

What breaks the symmetry between the electromagnetic and weak nuclear force?

I know the electromagnetic force is mediated by a photon and the weak nuclear force is mediated by two massive bosons. Are there any other insights into why the masses are so different?
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209 views

Weak isospin and types of weak charge

My understanding is that QCD has three color charges that are conserved as a result of global SU(3) invariance. What about SU(2) weak? Does it have two types of charges? What I'm getting at is: U(1) ...
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3answers
264 views

Effective operator in four-fermion interaction

In one book, I have got the following lines which I found myself unable to understand what is effective operator? The paragraph is given below: The weak interaction describes nuclear beta decay, ...
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0answers
110 views

Why does the electron energy distribution from muon decay peak near the kinematic maximum?

I'm trying to understand why when you have a muon decay event, the energy of the electron peaks near the maximum kinematically allowed value. Is there an intuitive explanation for why this is the case ...
3
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2answers
515 views

What is difference between the different 'flavours' of neutrinos?

Moreover, how-come scientist know that muon-neutrino are different from electron-neutrino when they didn't even know what the difference was? Did they interact differently with other particles?
3
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2answers
150 views

Playground of Forces

Why is it that the gravitational force acts on large sized objects while the strong and weak nuclear forces act at subatomic levels only? What is that stops each other to enter each others domain?
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1answer
405 views

Weinberg angle measurement methods

I was reading up on the history of $W/Z$ bosons today and I got a little puzzled. I always assumed that people measured $M_Z$ and $M_W$ and then derived the Weinberg angle. But it appears that they ...
2
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1answer
960 views

Jarlskog Invariant and its mathematical origin

CP violation is present in the weak interactions if There are no degeneracies in the up-quark/down-quark matrices The Jarlskog invariant $J=Im(V_{us} V_{cb} V_{ub}^* V_{cs}^*)$ is nonvanishing ...
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0answers
105 views

What would the universe be like if Electroweak symmetry were unbroken? [duplicate]

Possible Duplicate: What happens to matter in a standard model with zero Higgs VEV? What if the Higgs did not have a "Mexican hat" potential and the therefore it's vacuum expectation value ...
2
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1answer
259 views

4th order feynman-diagrams for $e^- + \mu^+ \to \nu_e + \bar{\nu}_\mu$

The task is to draw the two 4th-order Feynman diagrams of: $$e^- + \mu^+ \to \nu_e + \bar{\nu}_\mu $$ I drew the first one as (time left->right): ...
15
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2answers
764 views

Why is the (free) neutron lifetime so long?

A neutron outside the nucleus lives for about 15 minutes and decays mainly through weak decays (beta decay). Many other weakly decaying particles decay with lifetimes between $10^{-10}$ and $10^{-12}$ ...
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1answer
191 views

Can action of the weak and strong forces be reduced to action of electromagnetic force?

It is known that electromagnetic (EM) fields action on particles is limited to the Lorentz force action. In terms of spinors and currents, the EM field: (i) rotates the Dirac current around the ...
6
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1answer
679 views

CP Violation of the CKM Matrix

Considering the relation between the $SU(2)_{WEAK}$ partners of the $|u \rangle$, $|c \rangle$, and $|t \rangle$ mass eigenstates and the corrseponding downtype eigenstates $ \left( ...
2
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0answers
196 views

Can the mass of longitudinal and transverse W bosons be measured separately?

Some higgsless unified models of particle physics predict that the mass of longitudinally polarized W bosons and the mass of transversely polarized W bosons are different. In those models, a ...
4
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2answers
238 views

interaction at a distance: how it works

In classical physics, I know the forces due to gravity and electrostatics. I know a lot of work has been done, but don't know the status. Is there a generally accepted theory of how the force is ...
7
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3answers
950 views

Why does the weak force distinguish left and right handedness?

I'm wondering why the weak interaction only affects left-handed particles (and right-handed antiparticles). Before someone says "because thats just the way nature is" :-), let me explain what I find ...
8
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1answer
500 views

Do color-neutral gluons exist?

If I'm correct a quark can change color by emitting a gluon. For example a blue up quark $u_b$ can change into a red up quark by emitting a gluon: $$u_b \longrightarrow u_r + g_{b\overline{r}}$$ ...
4
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2answers
302 views

Sterile Neutrinos as Dark Matter

There has been recent activity by astrophysicists to determine whether a fourth flavor of neutrino, a sterile neutrino, exists. It would likely be more massive than electron, muon or tau neutrinos. ...
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5answers
4k views

How come neutrons in a nucleus don't decay?

I know outside a nucleus, neutrons are unstable and they have half life of about 15 minutes. But when they are together with protons inside the nucleus, they are stable. How does that happen? I got ...
4
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1answer
342 views

Why does parity violation in weak decay imply decay asymmetry?

I googled the sentence in the title of this question and found the famous experiment by Wu et al demonstrating that electrons in weak decay are emitted ``in the direction of motion of a left-handed ...
1
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1answer
763 views

Quantum numbers of the helicity states of the W boson

What are the weak hypercharge and weak isospin quantum numbers of the helicity states of the $W^\pm$ and $Z^0$ bosons? The W boson is a spin-1 massless particle. Consequently it has three helicity ...
2
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1answer
245 views

How much CP violation does the weak force cause?

I'm looking for the most readable quantitative explanation, with the least amount of difficult mathematics. Rather than an answer with just a number, I'd like to see the derivation from the CKM ...
13
votes
4answers
3k views

How to explain the weak force to a layman?

I'm trying to explain in simple terms what the weak interaction does, but I'm having trouble since it doesn't resemble other forces he's familiar with and I haven't been able to come up (or find on ...
1
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2answers
292 views

Is there a relationship between Berry-Pancharatnam phase and CP violation in quark mixing?

Berry-Pancharatnam phase is the phase that quantum systems exhibit when they pass through a sequence of states and return to their original state. It's a complex phase and it is different from the ...
3
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3answers
527 views

Energy of the electron-muon reaction

Lets see the reaction: $e^- \mu^- \to e^- \pi^- \nu_\mu \;\;\;\;\;\;\;\;\;\;\; {(1)}$ I suppose, that this reaction occurs as follows $e^- \mu^- \to e^- \mu^- \pi^+ \pi^- \to e^- \pi^- \nu_\mu$ Is ...