  We give a pragmatic/pedagogical discussion of using Euclidean path integral
in asset pricing. We then illustrate the path integral approach on short-rate
models. By understanding the change of path integral measure in the
Vasicek/Hull-White model, we can apply the same techniques to "less-tractable"
models such as the Black-Karasinski model. We give explicit formulas for
computing the bond pricing function in such models in the analog of quantum
mechanical "semiclassical" approximation. We also outline how to apply
perturbative quantum mechanical techniques beyond the "semiclassical"
approximation, which are facilitated by Feynman diagrams.
