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## Main Question or Discussion Point

Hi everybody!

While reading Peskin-Schroeder, i stuck in the in equation 5.4 about the unpolarized cross section of the [tex]e^- e^+ \rightarrow \mu^- \mu^+[/tex] annihilation. i didn't understand how this relationof the electron trace came to be, and where the indices came from?

[tex] \operatorname{tr}[(p\!\!/^\prime-m_e) \gamma^\mu (p\!\!/ + m_e) \gamma^\nu] = 4[p^{\prime \mu} p^\nu +p'^\nu p^\mu - g^{\mu \nu} (p \cdot p' + m^2_e)] [/tex]

thanx in advanced!

While reading Peskin-Schroeder, i stuck in the in equation 5.4 about the unpolarized cross section of the [tex]e^- e^+ \rightarrow \mu^- \mu^+[/tex] annihilation. i didn't understand how this relationof the electron trace came to be, and where the indices came from?

[tex] \operatorname{tr}[(p\!\!/^\prime-m_e) \gamma^\mu (p\!\!/ + m_e) \gamma^\nu] = 4[p^{\prime \mu} p^\nu +p'^\nu p^\mu - g^{\mu \nu} (p \cdot p' + m^2_e)] [/tex]

thanx in advanced!