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Does the Z boson couple to photons?

  1. Apr 16, 2010 #1
    Hi I can't find a Feynman rule for the coupling of two Z bosons to a photon. Does the Z boson couple to a photon at all?
  2. jcsd
  3. Apr 16, 2010 #2


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  4. Apr 16, 2010 #3
    You can get Z+Z -> gamma + gamma.
  5. Apr 16, 2010 #4
    zz to fermion to 2gamma

    zzA is not in the SM lagrangian
  6. Apr 16, 2010 #5


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    That's what I say: the only direct vertex is

    W+ + W- => Z0 + Photon

    but via intermediate states you can get (nearly) anything you like.
  7. Apr 16, 2010 #6

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    There are no all-neutral gauge boson couplings in the SM.

    It's easiest to see this by working in the w1, w2, w3, B basis rather than the W+/-, Z, A basis.

    Tom is right, these can appear at loop level, but these will be second-order weak and GIM surpressed. However, you still have to comply with conservation laws. For example, you can't get any electric dipole radiation because the Z is neutral. I need to think more about magnetic dipole and electric quadrupole.
  8. May 3, 2010 #7
    The coupling of gauge bosons self interaction in non-abelian gauge theory is proportional to f_{abc}, i.e. only diffrent bosons can interact. So, no Z-Z-A and no Z-Z-Z interactions. You can also think that photon only couple to charged particles directly.
  9. May 4, 2010 #8


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    I do not see how this applies directly. In the el.-weak theory we have U(1)*SU(N); in addition the photon is "mixed" according to the original basis.
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