quantum field theory - Is there a mistake in a QFT textbook? - Physics Stack Exchange

I tried to calculate one of the problems in the textbook Gauge Theory of Elementary Particle Physics by Ta-Pei Cheng and Ling-Fong Li. On page 248 you can find the following calculation of a loop

quantum field theory - Normal ordering of hamiltonian - Physics Stack Exchange

Quantum Field Theory and Gravity: Conceptual and Mathematical

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quantum field theory - What is the missing part of the argument needed to justify the claim of (2.52) in Peskin and Schroeder's QFT textbook? - Physics Stack Exchange

quantum field theory - How are real particles created? - Physics Stack Exchange