I have small question computing vacuum expectation values here http://www.cns.gatech.edu/FieldTheory/extras/SrednickiQFT03.pdf" [Broken] from Mark Srednicki.(adsbygoogle = window.adsbygoogle || []).push({});

My problem is with equation 210 on the pdf page 69. In the second line of 210, where does the second term come from?

Z(J) and W(J) are defined one page 62-63 with equations 196 and 197, and the computation for the vacuum expectation value of a single field is given in 198, which makes sense to me.

But not the second term in the second line of 210!

thank you

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# Computing vacuum expectation values

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