Abstract
In this paper we prove that any convex body of the d-dimensional Euclidean space (d ≥ 2) possesses at least one shortest generalized billiard trajectory moreover, any of its shortest generalized billiard trajectories is of period at most d + 1. Actually, in the Euclidean plane we improve this theorem as follows. A disk-polygon with parameter r > 0 is simply the intersection of finitely many (closed) circular disks of radii r, called generating disks, having some interior point in common in the Euclidean plane. Also, we say that a disk-polygon with parameter r > 0 is a fat disk-polygon if the pairwise distances between the centers of its generating disks are at most r. We prove that any of the shortest generalized billiard trajectories of an arbitrary fat disk-polygon is a 2-periodic one. Also, we give a proof of the analogue result for ε-rounded disk-polygons obtained from fat disk-polygons by rounding them off using circular disks of radii ε > 0. Our theorems give partial answers to the very recent question raised by S. Zelditch on characterizing convex bodies whose shortest periodic billiard trajectories are of period 2.
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References
Benci V., Giannoni F.: Periodic bounce trajectories with a low number of bounce points. Ann. Inst. H. Poincar Anal. Non Linaire 6(1), 73–93 (1989)
Bezdek K., Connelly R.: Covering curves by translates of a convex set. Am. Math. Mon. 96(9), 789–806 (1989)
Bezdek K., Lángi Zs., Naszódi M., Papez P.: Ball-polyhedra. Discrete Comput. Geom. 38, 201–230 (2007)
Bonnesen T., Fenchel W.: Theorie der konvexen Körper. Springer Verlag, Berlin (1974)
Farber M., Tabachnikov S.: Topology of cyclic configuration spaces and periodic trajectories of multi-dimensional billiards. Topology 41(3), 535–589 (2002)
Ghomi M.: Shortest periodic billiard trajectories in convex bodies. Geom. Funct. Anal 14, 295–302 (2004)
Tabachnikov, S.: Geometry and billiards. Am. Math. Soc. (2005)
Zelditch S.: Spectral determination of analytic bi-axisymmetric plane domains. Geom. Funct. Anal. 10(3), 628–677 (2000)
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K. Bezdek partially supported by a Natural Sciences and Engineering Research Council of Canada Discovery Grant.
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Bezdek, D., Bezdek, K. Shortest billiard trajectories. Geom Dedicata 141, 197–206 (2009). https://doi.org/10.1007/s10711-009-9353-6
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DOI: https://doi.org/10.1007/s10711-009-9353-6