title: Nonperiodic orbit sums in Weyl's expansion for billiards.
abstract: Weyl's expansion for the asymptotic mode density of billiards consists of the area, length, curvature, and corner terms. The area term has been associated with the so-called zero-length orbits. Here, closed nonperiodic paths corresponding to the length and corner terms are constructed.
authors.affiliation: Institute of Theoretical Physics, Academia Sinica, Beijing 100080, China.
authors.forename: W M
authors.initials: WM
authors.lastname: Zheng