I'm confused about index calculation in eq. 8.25, Mandl QFT textbook. Can anyone give me a detailed explanation showing the equality below?(adsbygoogle = window.adsbygoogle || []).push({});

[itex]X=\frac{1}{2}A_{\delta \alpha}^+(\bf{p'})\Gamma_{\alpha \beta}(\bf{p'})A_{\beta \gamma}^+(\bf{p})\widetilde{\Gamma}_{\gamma\delta}[/itex]

[itex]=\frac{1}{2}Tr[A^+(\bf{p'})\Gamma A^+(\bf{p})][/itex]

Please be patient, I'm learning index notation from scratch.

Thanks.

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# Trace as a product of operators

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