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For the process $e^+e^-\rightarrow \gamma \gamma$ Schwartz gave following Feynman diagram in section 9.4

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I think the diagram is wrong since it didn't conserve charge at both the vertices. The correct diagram should have an internal propagator of either $e^-$ or $e^+$. Also, the particle flow direction for $e^+$ in the lower-left section should be in reverse direction.

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The mistake you mention was in the first edition and should have been corrected in future editions of the book. See errata here: schwartzqft.fas.harvard.edu/first-edition-corrections. Make sure you work with the fourth (latest) edition since there were many small mistakes (and a couple big ones) in the book. The mistakes in the diagram are 1) internal line should be a scalar and 2) the arrows should be reverse in the e^+ line.

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  • $\begingroup$ the virtual should be an $e^-$ arrow from top to bottom. electrons are not scalars. $e^+$ usualy a positron read as an electron with the arrow in the opposite direction to the momentum. $\endgroup$
    – anna v
    Commented Jun 13, 2020 at 7:15
  • $\begingroup$ I usually see ghost fields represented with dotted lines $\endgroup$
    – Triatticus
    Commented Jun 13, 2020 at 7:21
  • $\begingroup$ @annav in that section he is doing scalar QED so the “electrons” are scalars. $\endgroup$
    – Prahar
    Commented Jun 13, 2020 at 9:47
  • $\begingroup$ @Triatticus ghost fields have dotted lines. Scalars have dashed lines. $\endgroup$
    – Prahar
    Commented Jun 13, 2020 at 9:47

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