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Red quark going to a red quark via an gluon emission

  1. Aug 15, 2013 #1
    Hi, I'm currently doing a course in particle physics at masters level and I have this problem:

    I know that having an red:anti-red gluon isn't possible as this produces an non-zero trace for its representation, but if I have a red quark that emits a gluon and afterwards is still a red quark, what would be the possible gluon combinations/colors? is it just the two linear combinations: (R:aR - B:aB)/sqrt(2) and (R:aR + B:aB - 2G:aG)/sqrt(6) ???

    Thanks in advance
  2. jcsd
  3. Aug 15, 2013 #2
    never mind I found out
  4. Aug 16, 2013 #3


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    That's not possible b/c the gluons living in the adjoint rep. of su(3) always change color. A process where the quark color is not affected is possible only in u(3) = su(3) + u(1) where the last u(1) term corresponds to a color-neutral force which would look like QED.
  5. Aug 16, 2013 #4
    In a common presentation of SU(3) operator matrices, two of them won't change color, but will give different phases to different colors.

    A colorless operator would give the same phase to every color.
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