Tagged Questions

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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The role of W bosons in the weak nuclear force and beta decay

I am a beginner Physics student and I am studying the weak nuclear force and how particle interactions work. Now, from my book and the Feynman diagram, I learned that a neutron can change into a ...
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0answers
23 views

Why do weak interactions give such slow decay rates, if the analog of the fine structure constant isn't signifigantly small?

Intuitively, it seems as though the reason would be a small value for the coupling constant, as the probability for emitting $W^{-}$ bosons would be low. However, it's value is almost the same as the ...
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2answers
51 views

What is the Weak force?

In this Particle Physics books I'm reading it explains Weak force with Beta Decay, a Neutron turns into a Proton after emitting an electron, so after it emits an electron one of the neutrons ...
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1answer
30 views

Gluons, the Weak Force, or both?

I've recently been reading about how the Weak Force holds quarks together to make protons and neutrons. But before learning about that specifically, I found out about Quark-Gluon Plasma, leading me to ...
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2answers
95 views

Is there a strong evidence of antineutron existance?

Wikipedia explains: The antineutron was discovered in proton–proton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by Bruce Cork in 1956, one year after the antiproton was ...
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2answers
94 views

Is neutron decay a purely electromagnetic phenomena?

Until reading the Phys.SE post here about the neutron decay I never feel strange the fact about the antisymmetricity of this decay. But indeed why this decay is antisymmetric. The neutron is his own ...
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1answer
58 views

Weak interaction violate charge conjugate

How can we show that the weak interaction violates the charge conjugation symmetry?
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0answers
36 views

How does dark matter interact with light?

Most articles I read say that dark matter are weakly interacting particles. Are there any theories on how dark matter may interact with light/electromagnetic radiation?
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1answer
132 views

Value of weak force coupling constant

I'm trying to get my head around the weak force coupling constant $\alpha_w$ but getting confused by different resources. Hyperphysics suggests it is tiny compared with the strong force coupling, ...
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1answer
77 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
82 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
130 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
30 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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2answers
48 views

Kaon reaction rates

I have a big difficulty in grasping weak interactions. For example, how would I go on about determining the following: $\frac{\Gamma(K^{+} \to \pi^{+}K^{0})}{\Gamma(K^{+} \to \pi^{0}K^{+})}$ I ...
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1answer
76 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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1answer
91 views

From a cross section to a probability

This is homework problem: Given the cross-section of a neutrino-electron scattering, what is the probability for a solar neutrino to scatter with a electron as it goes through the center of the Earth? ...
3
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1answer
55 views

Two ways of looking at weak current?

A weak current of the form: $$j^\mu=\bar u_e \gamma^\mu \frac{1}{2}(1-\gamma^5)u_\nu$$ implies that it automatically selects the left-handed neutrino. This current can also be written as: $$j^\mu=\bar ...
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0answers
118 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
88 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
25 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
265 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
52 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 - ...
1
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1answer
67 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
81 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
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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
166 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
173 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 ...
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1answer
221 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
57 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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54 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
169 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
218 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
votes
1answer
426 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
291 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 ...
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3answers
975 views

What stabilizes neutrons 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
votes
1answer
341 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?
2
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0answers
223 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
314 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
117 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
votes
2answers
690 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?
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2answers
154 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
524 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
1k 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
276 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): ...
21
votes
3answers
1k 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
194 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 ...
7
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1answer
777 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( ...
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0answers
205 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 ...