The question from Scattering Amplitudes in Gauge Theory and Gravity page 46, equation (2.120) from which I can't get a consistent formula.

I just calculate A3(gff) which two fermion and one gluon $A_n\left[\ldots,f^+_{i-1},i^−,f^-_{i+1},\ldots\right]$ sign show helicity of particle.

Use Feynman diagram of qed soft-photo from Peskin page 182 equation (6.20). 1

I get formula of the first term of (2.120) as $$-\frac{\langle i+1,i \rangle[q,i-1]}{[qi] s_{i,i+1}}$$ instead of the one shown below. 2

Which is the correct formula?

  • 1
    $\begingroup$ Elvang anf Huang's metric convention is mostly positive, P$\&$S is mostly negative. Have you taken care of this? $\endgroup$ – Oбжорoв May 1 at 12:06

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