Quantum scars and classical ghosts

In this paper we demonstrate that state scarring is a more pervasive and subtle phenomenon than commonly believed. We show that scars can exist in regions where there are no periodic orbits, and that they are due to families of neutrally stable orbits that reside in a neighboring system (‘‘ghosts’’). Furthermore, seemingly unscarred diffuse states can turn out to be supported by a single extensive family of periodic orbits.