What is Weak interaction: Definition and 60 Discussions

In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms. The weak interaction participates in nuclear fission, and the theory describing its behaviour and effects is sometimes called quantum flavourdynamics (QFD). However, the term QFD is rarely used, because the weak force is better understood by electroweak theory (EWT).The effective range of the weak force is limited to subatomic distances, and is less than the diameter of a proton. It is one of the four known force-related fundamental interactions of nature, alongside the strong interaction, electromagnetism, and gravitation.

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  1. S

    I Fixing CP phases to cancel CKM phases

    When we try to see if the weak sector is CP invariant, we CP transform all the fields in the charged interactions terms and we get a condition involving the elements of the CKM matrix and the arbitrary phases of the CP transformed fields: $$V_{ij} = V^*_{ij} \, e^{i(\xi_W + \phi_{d_j} -...
  2. H

    A Is the weak interaction asymptotically free?

    Is the ##SU(2)_L## part of the SM asymptotically free like a typical non-Abelian gauge theory? I've been made to understand that confinement does not occur for ##SU(2)_L## because the spontaneous symmetry breaking scale is above the confinement scale, however I can't find any information on...
  3. S

    I Conductors and weak interaction

    Are there any plausible semiconducting or superconducting devices which would show clear parity violation? Electrons in matter are governed overwhelmingly by electromagnetic interactions. Electron-electron, and electron-nuclei. However, there is in principle some weak interaction. Elastic weak...
  4. W

    I Detection of Neutral Currents

    In decay processes where no mixing between quark families is present, the mediator of the weak force is the neutral ##Z^0## boson. If that is the case, how is it experimentally possible to detect neutral currents in processes such as: $$\bar{\nu}_\mu + e \rightarrow \bar{\nu}_\mu + e$$ What...
  5. S

    I When is weak interaction a force?

    When is weak interaction actually a force, rather than merely cause of some process? Not in beta decay - it is process. There are simpler weak interaction processes around: elastic scatterings that change only momentum but not taste. But those are still processes and are over as the particles...
  6. DHO232

    I Does a photon experience time while interacting with the weak force?

    Long time reader, first time posting here in physics forums. I know that according to relativity photons have no proper time. I also know that a photon of sufficient energy can interact with a nucleus's nuclear force via the weak interaction resulting in pair production. I was looking at a...
  7. P

    I Weak interaction between electrons

    The two electrons will be repelled by electrostatic force, but they interact with weak force, means that in addition to the electrostatic force between the electrons there will be weak force?
  8. Gene Naden

    I Weak interaction - is it a force?

    A friend, well-read in popular accounts of physics, posted the following question to me: is the weak force attractive or repulsive? Now I have read about the weak interaction. I know that it violates parity, that it is involved in beta decay, that it unifies with the electromagnetic interaction...
  9. C

    I Measuring characteristic time of strong and weak interaction

    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 force (time of interaction ##t_1\sim 10^{-23}s##, which is also the time of generation of c and d)...
  10. Superfluid universe

    I What is the charge for the weak interaction?

    We have the electric charge for the electromagnetic force, the color charge for the strong force. What is the charge for the weak force? Thank you. :)
  11. A

    I Energy conservation concerns in the weak interaction

    I have a few questions: Can a u quark turn into a d quark (heavier) via the weak interaction? If so, how is the mass/energy shortfall made up? How can the (supermassive) carrier bosons (W, Z) be called into being? Where does the energy come from? Or is the energy bill unpaid because they are...
  12. D

    A Data needed for fall off of weak interaction vrs distance

    I'm trying to find measurements for the weak interaction at various distances. Any suggests for search terms or relevant paper would be appreciated. Thanks, Dan
  13. P

    I Time invariance of weak interaciton e-p->\nu n

    The question is rather simple, but I cannot seem to find a solid answer. I need the cross section of the following interaction: e^- + p\rightarrow n+ \nu . I need the cross section using the form factors. There are many solutions for the interactions like: n+ \nu\rightarrow e^- + p or...
  14. charlesmartin14

    B In Fermi V-A theory, where does the Weak Interaction occur

    Where is the electron-nucleon interaction? On the surface of the nucleus, or at the origin (R-0) ?
  15. Kara386

    Can this neutrino be detected via a CC weak interaction?

    Homework Statement A tau neutrino with energy 1GeV interacts with a stationary neutron. Can the neutrino be detected via a charged current interaction? Take the mass of tau to be 1784MeV/c##^2##, 105MeV/c##^2## for the muon and 939MeV/##c^2## for the neutron. Homework EquationsThe Attempt at...
  16. charlesmartin14

    A Is beta decay a weak charge-current processes?

    Im try to understand this paper http://citeseerx.ist.psu.edu/vie... and see if I correctly understand which processes are charge-current processes, and which are charge neutral, as listed in Figure 1. Thanks
  17. T

    I Question about Chirality and the Weak Interaction

    Hello, From my understanding, the weak interaction only acts of Left-Handed Chiral Particles, and Right-Handed Chiral Anti Particles. There have been observed fermions (other than neutrinos, where all observed neutrinos are Left Handed Chiral) where some are left handed and some are right...
  18. R

    I What is the weak isospin of hadrons?

    What are the weak isospins (T3 values) of various hadrons, including the proton, neutron, mesons, hyperons and other hadrons? How is the weak isospin calculated for any hadron? Published sources provide T3 only for fundamental fermions, that is, quarks and leptons. In the fundamental bosonic...
  19. 1

    I I don't understand this Feynman Diagram

    Question: Draw the lowest-order Feynman diagrams for the e+e- --> W+W-process The answer gives three diagrams. I understand the first two, but the third makes no sense to me. Here it is: So this is a t-channel Feynman diagram. As far as I can tell regarding how these types of Feynman diagrams...
  20. S

    A Exploring Chiral Symmetry in Weak Interaction

    Dear all Do we have chiral symmetry for weak interaction? I know that weak interaction is chiral. thank you
  21. N

    Running Coupling for Weak Interaction

    How can I derive the running coupling for the weak interaction. I have found derivations for QED and QCD that involve the β function http://www.physics.umd.edu/courses/Phys741/xji/chapter1.pdf but I can't find anything specific for the WI. Thanks.
  22. Anchovy

    Weak interaction SU(2) gauge fields W^{1,2,3} and charge?

    When we start by postulating local SU(2) gauge invariance for our weak isospin doublets \begin{align} \psi &= \begin{pmatrix} \nu_{e} \\ e^{-} \end{pmatrix}_{L} \end{align} etc., we have to introduce massless gauge fields to preserve the Lagrangian's invariance. For SU(2) this demands 3...
  23. U

    Experiments to distinguish 3-body and 2-body decays?

    I was wondering are there any experiments to distinguish between 2 and 3-body decays? For example, consider decay of the muon and the pion: The pion only emits 1 muon neutrino ("missing energy") and 1 muon. The muon however, emits 1 muon neutrino, 1 electron neutrino and 1 electron. How is...
  24. U

    Production of Z boson - Cross Section

    Homework Statement Calculate the ratio ##R = \frac{\sigma_{had}}{\sigma_{\mu+\mu-}}## for energy around ##10~GeV##. At sufficiently high energies, the ##e^+e^- \rightarrow \mu^+ \mu^-## reaction can proceed via the ##Z^0## boson. Assuming vertex factors for EM and weak interaction are the same...
  25. AlanKirby

    Why can only the weak interaction change quark flavour?

    Hi there, so my question is as follows. I understand that only the weak interaction can change the flavour of a quark, but why? Idea 1: It's due to the change in flavour also meaning a change in mass, thus a massive exchange particle is needed (gravity is negligible so forget the massive...
  26. L

    Interpretation of a before $\gamma^{5}$ in J$_{\alpha}$

    Could you explain what's the interpretation of a before \gamma^{5} in this current: J_{\alpha}=\bar{\psi_{e}}\gamma^{\alpha}\left(1-a\gamma^{5}\right)\psi_{\nu_{e}} +\bar{\psi_{\mu}}\gamma^{\alpha}\left(1-a\gamma^{5}\right)\psi_{\nu_{\mu}}? And will this factor complicate calculations of decay...
  27. U

    How Do You Calculate Cross Sections in Electron-Neutrino Scattering?

    Homework Statement [/B] (a) Find the ratio of cross sections. (b) Find the cross section for electron-neutrino scattering by first writing down relevant factors. Homework EquationsThe Attempt at a Solution Part (a)[/B] These represent the neutral current scattering for the muon-neutrino and...
  28. U

    What is this mystery particle - LHC?

    Homework Statement (a) Draw the feynman diagram for ##p \bar p \rightarrow## reaction. (b) Find an expression for mass of the particle. (c) Find an expression for number of ##\mu^{+} \mu^{-}## produced. (d) Find an expression of ##n_{jj}## in terms of ##m_{inv}## and its spin. (e) Deduce the...
  29. U

    Special H boson with very high cross section?

    Homework Statement (a) Explain the results. (b) Why is the cross section much higher? Suggest the dominant decay product pair.[/B] Homework EquationsThe Attempt at a Solution [/B] Part(a) For a centre of mass energy of ##170GeV##, you produce pairs of oppositely charged ##W^{\pm},W^{\mp}##...
  30. haael

    V - A weak interaction theory?

    Does anyone know any good introduction to V-A weak interaction theory?
  31. mokeejoe5

    Understanding the Weak Interaction: What Causes It & What is Its Range?

    Recently it struck me that I'm not sure I understand the weak interaction at all. What causes it to happen? I know that its mediated by the W and Z bosons and has a short range as a result of the large mass these bosons posses, but what does that range refer to? Range from what?!
  32. K

    Why EM and weak interaction are unified

    In SM, people say the ##SU(2)\otimes U(1)## theory unify the EM and weak interaction. I understand that the two interactions both originate from the electroweak theory in a mixed way. But does this mean they are unified? Since when we talk about unification like GUT, we require the couplings run...
  33. Primroses

    How to Determine the Range of Strong and Weak Interaction

    How can we determine the ranges of strong interactions and weak interactions? Can calculations of relevant scattering cross sections do this? Thanks.
  34. M

    Universe With No Weak Interaction

    Hello, I have a homework problem posing the following hypothetical situation Imagine a hypothetical universe in which weak interactions do not exist and only first-generation quarks and leptons are present (i.e. there are no charm, strange, top or bottom quarks, and no muons, muon...
  35. N

    What is the charge of weak interaction?

    The strong interaction has color ''charge'',the electromagnetic interaction has electric charge,the gravity interaction has mass ''charge'',then what is the charge in weak interaction? Each interaction corresponds to a symmetry.Symmetry SU(3) for strong interaction, SU(2)xU(1) for...
  36. binbagsss

    Stars, fusion, how exactly the weak interaction acts ?

    I am currently reading E=Mc^2 and have a quick question regarding some of the nuclear fusion they describe that takes place in stars: When proton fusion occurs, one of the protons decays into a neutron + positron + neutrino – due to the weak interaction. And the proton and neutron , acted...
  37. N

    Why CP symmetry is violated in weak interaction?

    Please teach me this: Why is CP symmetry violated in electro-weak interaction? Is it correct that because of the mass of neutrino is zero(so that the left and righ neutrinos do not mix with each other)? Thank you very much in advance.
  38. D

    Finding Range of Weak Interaction from Mass of Z Boson

    Homework Statement One of the mediators of the weak interactions is the Z boson, which has a mass of 91 GeV/c 2. Use this information to find an approximate value for the range of the weak interaction. Homework Equations This is the part that I am having trouble with. I don't know where to...
  39. M

    Where does the energy of a destroyed W boson go?

    Hello. I'm new so I am uncertain to which forum this post should be posted in so I'll just leave this here. Anyways, I was reading about the four fundamental forces and it came to my mind that the W boson is 80.4 GeV, whilst the two lepton that are excreted upon destruction are 0.511 MeV...
  40. R

    Feynman diagram for weak interaction.

    For a leptonic weak interaction diagram, we have an election converted into a neutino and emitting a w- particle. But only left handed part should undergo weak interaction. So basically you should have the left handed part of electron converted into a neutrino(left handed) emitting a w-...
  41. K

    Exploring Weak Interactions: Gravitational, Electrodynamics, Nuclear, and Quarks

    Gravitational force between masses is given by the law of universal gravitation. Electrodynamics force between electric charges is the Lorentz force. Nuclear force between nucleons falls off exponentially with rising the distance. The force between quarks grows in proportion to the distance. Can...
  42. MathematicalPhysicist

    Question regarding CP symmetry and weak interaction

    I have the next decay: B^0 \rightarrow D^+ e^- \nu_e The question is: employ CP symmetry on the particles in this process, what reaction would you get? and what would happen if CP symmetry breaks? Now if I employ CP symmetry I get: B^0 \rightarrow D^- e^+ \bar{\nu_e} But in my...
  43. S

    Shift in energy due to weak interaction

    Homework Statement A particle is in a box of length L on x-axis. 0<x<L. What is the first order shift due to V(x) of the wavefunction? Homework Equations H=p2/2m Sin=sqrt(2/L)cos(npix/L) En=n2pi2hbar2/2mL2 V(x)=kx2/2 The Attempt at a Solution I'm super confused because the shift in the...
  44. DocZaius

    Understanding Weak Interaction Field in Beta Decay

    I've had trouble understanding how the weak interaction could be field based, like classical gravity, or electromagnetism. My limited understanding of the interaction so far had been that left handed leptons and quarks would have an event spontaneously happen to them (such as decay). I thought...
  45. E

    Weak interaction, fusion, and tunneling

    I have 2 questions... I was told that the transmutation of Li-7 to Be-8 by proton collisions at energies below the classical barrier verifies the QM description of the weak interaction cross section. Firstly, I found the leap in logic very confusing - does the weak force have a role in...
  46. V

    Is My W and Z Bosons Mini Thesis Covering All Key Topics?

    Hi, Im currently writing a theory section for the W and Z bosons mini thesis type project, I am looking to fully cover the main topics in this area and am wondering if i am missing any or need to re-order things: Overview of elementary particles Symmetry and conservation laws Gauge...
  47. R

    Deriving 4-Point Fermi Interaction from Standard Model

    Can someone explain how one derives the 4-point Fermi interaction from the full Standard Model? I understand you set up a cutoff \Lambda, and the cost of this is that the coefficients of all terms in your Lagrangian become functions of this cutoff, and you also have an infinite number of new...
  48. K

    Weak interaction left handed v. right handed

    (correct me if i state anything wrong) the weak interaction only works on left handed particles and right handed antiparticles; so if there was a right handed muon what would it decay into? and is it possible for a left handed particle to become a right handed particle? (not just a change of...
  49. X

    Electron-positron pair creation by weak interaction?

    Hello, Im trying to find out if, since an electron positron pair can anhillate to produce a muon-anti muon pair by the weak interaction, can the same thing occur for the production of an electron/anti-electron pair? Or would it just happen by the electromagnetic force? Or both, with the weak...
  50. F

    Why is the helicity of a neutrino unchanged by the weak interaction?

    Hi... Consider a neutrino with a Dirac mass m_\nu and the weak interaction {\cal{L}}=\frac{g}{2 \sqrt{2}} \sum_l[{W_{\mu}^+ \cdot \bar{\psi}_{\nu_l} \gamma^{\mu}(1-\gamma_5)\psi_l + W_{\mu}^- \cdot \bar{\psi}_{l} \gamma^{\mu}(1-\gamma_5)\psi_{\nu_l} }\right{]} + \frac{g}{4...
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