Hello! I am reading about Klein Gordon operator from Peskin book and he reaches at a point the integral ##\int_0^\infty \frac{1}{p^2-m^2}e^{-ip(x-y)}dp^0##. He then explains the different approaches of doing this integral, depending on how you pick the contour around the 2 poles. Why does the contour matter? One should get the same result in the end, no matter how you twist your contour around the poles (some ways are easier to solve but the result should be the same in the end). So what is the point of all this? Thank you!(adsbygoogle = window.adsbygoogle || []).push({});

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# I Klein Gordon propagator

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