I need help solving the following integral:
$ \int_{0}^\infty dx \ x^{-1} K_{i a}( x) K_{i b} (x) $
I got it in the middle of a physics problem. I know that it must be proportional to $ \delta(a-b)$, but I couldn't find the proportionality constant. I thought about using the integral 6.576.4 from Gradshteyn (2007), but the conditions there are not met.