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R2

From IFPA wiki

1. Derive the expression of the 3-gluon vertex.

2. Calculate the colour factors of the following diagrams: Diagrams.png

3. The square amplitude of the process [math]\displaystyle{ q\bar q\to gg }[/math] can be represented by the following classes of diagrams:

Qqgg.png

a) For each diagram, calculates the colour factor.

b) Adapt the answer for [math]\displaystyle{ e^+e^-\to\gamma\gamma }[/math] to obtain the expression of the first two diagrams as a function of s, t and u, neglecting quark and lepton masses.

c) Calculate the last diagram, which is a square.

The answer can be checked by taking m=0 in equation (8.12) of the Handbook of perturbative QCD (see references).


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