I have just learned from nice article(adsbygoogle = window.adsbygoogle || []).push({});

http://motls.blogspot.com/2013/12/edward-witten-what-every-quantum.html

that the propagator of a massive particle can be rewritten as an integral over the so-called Schwinger parameter t as

$$

\frac{1}{p^2 + m^2} = \int\limits_0^\infty dt \exp(-t(p^2 + m^2))

$$

In addition, in the blog article it is said that this Schwinger parameter p can be interpreted as the proper length of the propagator. I dont see this, so can somebody give a derivation/further explanation?

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# Why does the Schwinger parameter correspond to proper length?

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