Searchlight Asymptotics for High-Frequency Scattering by Boundary Inflection

Abstract

We consider an inner problem for whispering gallery highfrequency asymptotic mode's scattering by a boundary inflection. The related boundary-value problem for a Schrödinger equation on a halfline with a potential linear in both space and time appears fundamental for describing transitions from modal to scattered asymptotic patterns, and despite having been intensively studied over several decades remains largely unsolved. We prove that the solution past the inflection point has a "searchlight" asymptotics corresponding to a beam concentrated near the limit ray, and establish certain decay and smoothness properties of the related searchlight amplitude. We also discuss further interpretations of the above result: the existence of associated generalised wave operator, and of a version of a unitary scattering operator connecting the modal and scattered asymptotic regimes.