in peskin-schroeder and http://www.hep.phy.cam.ac.uk/batley/particles/handout_04.pdf" [Broken] the amplitude for [tex] e^-e^+\rightarrow \mu^- \mu^+ [/tex] is written using feynman rules as follows(adsbygoogle = window.adsbygoogle || []).push({});

[tex] -iM=[\bar{v}(p_2)(-ie\gamma^\mu )u(p_1)] \frac{-ig_{\mu\nu}}{q^2}[\bar{u}(k_1)(-ie\gamma^\nu )v(k_2)] [/tex]

but what about the delta function integeration? is it already done here?

thanks in advanced!

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# When can we ignore the delta function in th Feynman rules?

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