Determination of the border between 'shallow' and 'deep' tunneling regions for Herman-Kluk method by asymptotic approach

The evaluation of a tunneling tail by the Herman-Kluk method, which is a quasiclassical way to compute quantum dynamics, is examined by asymptotic analysis. In the shallower part of the tail, as well as in the classically allowed region, it is shown that the leading terms of semiclassical evaluations of quantum theory and the Herman-Kluk formula agree, which is known as an asymptotic equivalence. In the deeper part, it is shown that the asymptotic equivalence breaks down, due to the emergence of unusual "tunneling trajectory", which is an artifact of the Herman-Kluk method.
Comment: To be published in Phys. Rev. A