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Weak force and axial vector coupling

  1. Oct 26, 2011 #1
    Hi physics forum,

    I have been reading David Griffith's book "intro to elementary particles" and he
    describes the decay of the pi-meson as "pure axial vector"

    Can someone tell me what this means, in terms of the weak force vertex consisting of
    this factor


    Thanks, Mark
  2. jcsd
  3. Oct 26, 2011 #2

    Vanadium 50

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    Only the term with the gamma_5 in it contributes.
  4. Oct 26, 2011 #3
    Thanks for the reply. I'll follow up 1) what does that mean physically, for example, do only certain particle types engage in pure axial coupling? 2) can you say a little as how
    the math would work (how can the vector part of V-A not contribute, since the axial
    part is multiplied by the vector (γuγ5

    I am a novice in this, so it may not be a good question! -Mark
  5. Oct 26, 2011 #4


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    db, The weak interaction is an interaction between weak currents, JμJμ. For the lepton pair the particles are free, and Jμ is of the V-A form.

    However the quarks that make up the pion are not free, they are in a bound pseudoscalar state. You can combine their wavefunction with the 4-momentum kμ to construct an axial vector current, but there is no way to make a vector current.
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