The result is the derivative of the modified Bessel function of the second kind, whose integral representation is
http://mathworld.wolfram.com/ModifiedBesselFunctionoftheSecondKind.html
And the solution for the massive case is given in Weinberg's QFT I page 387, which can be derived from the...
I'm watching some of the course video of the Perimeter International Scholar, and the professor always mention the wiki that their students can assess. Is there any way that I can assess too? I really want to read some of the lecture notes and tutorial. Thank you!
I'm working on this problem, too. But I really don't know how to start.
@lchigo449, that is a Quantum field theory book, and the only information related to this problem is the definition of semi-simple algebras.