# Why don't green and anti-green gluons immediately annihilate each other?

I can't believe I haven't found an answer elsewhere.....

I have read repeatedly about blue/anti-blue gluons, etc., but no reason as to why they don't destroy each other immediately.....

Or maybe they do? But only after they have carried the 'charge' between quarks?

Edit: What about a red-antigreen gluon and an antired-green one?

• You could ask this question in a much simpler context - when a gamma ray produces an electron-positron pair, why don't they immediately annihilate? The answer will likely be similar. Commented Jun 17, 2019 at 17:51
• There are no "green" gluons, nor "anti-green" ones. They transform in the adjoint. You may come up with charges of the type "green--anti-red" and so on.
– user178876
Commented Jun 17, 2019 at 17:53
• @marmot This is as good as an answer, if you wrote up a few framing sentences around it. The OP might not understand these two labels for a single particle.... Commented Jun 17, 2019 at 18:53
• Kurt, we don't have a set of gluons and a separate set of antigluons. Very roughly, a green quark can turn into a red quark by emitting a green-antired gluon, and if a red quark absorbs that gluon it will turn green. But that's just a rough "cartoon" of the actual QCD model. You need matrices & group theory to describe it properly. Commented Jun 17, 2019 at 20:02
• A single gluon has a color and an anticolor label. A green-antigreen gluon is the gauge QFT excitation coupling to a green quark and an antigen antiquark. As @marmot says, you cannot talk about three $\bar{G}G, ~ \bar{R} R, ~ \bar{B} B$ gluons, since they'd sum up to a color singlet, so no gluons. You must always be mindful that these are overstretched metaphors to summarize the math in codespeak, and hardly anything else. Taking these cartoons too seriously ignoring the math always leads to grief! Commented Jun 17, 2019 at 21:35

So the bottom-line is that, as long as you can form an invariant contraction of the incoming states, they can annihilate. In particular, gluons can, since their only quantum numbers are that they are octets under SU(3), and $$\boldsymbol{8}\times\boldsymbol{8}$$ contains a singlet. The annihilation rate may, however, be very much suppressed, as in the case of $$e^-\mu^+\to\gamma\gamma$$.