From Schwartz qft notes p. 257 or his qft book p. 455(adsbygoogle = window.adsbygoogle || []).push({});

1. Why and how does the integral in (24.24) go imaginary, when M > 2m? Is it because the logarithms can not take negative real numbers, thus we have to switch to complex numbers?

2. (24.25) is the principal value equation, right?

3. How does (24.26) follow from what?! Is the little theta the theta step function?

4. How does (24.27) follow from (24.26)?! Taking the integral of the theta function gives us this square root term?

thanks for any hints and help

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# A Imaginary parts of amplitues (Schwartz QFT text)

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