

Iskovskikh Seminar
March 22, 2012 18:00, Moscow, Steklov Mathematical Institute, room 540






On quadrilateral orbits in planar billiards
A. A. Glutsyuk^{abcd} ^{a} M. V. Lomonosov Moscow State University, Faculty of Mechanics and Mathematics
^{b} Independent University of Moscow
^{c} Laboratoire J.V. Poncelet, Independent University of Moscow
^{d} CNRS — Unit of Mathematics, Pure and Applied

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Abstract:
V. Ya. Ivrii's conjecture (1980) states that in every piecewicesmooth billiard in euclidean space the set of periodic orbits has measure zero. This conjecture is closely related to G. Weyl's conjecture from the spectral theory of the laplacian. Particular cases of Ivrii's conjecture for triangular orbits were proved by many authors,
first of all, M. Rychlik (1989, in dimension two) and Ya. B. Vorobets (1991, in every dimension).
The particular case for quadrilateral orbits in dimension two was proved in a joint work of Yu. G. Kudryashov and the speaker (for piecewisesmooth billiards with pieces smooth enough).
We will discuss partial results on the twodimensional complexalgebraic version of the Ivrii's conjecture, for reflections with respect to complex planar algebraic curves. It appears that in this context even the Ivrii's
conjecture for quadrilateral orbits is not true, and the counterexamples can be described. The nontrivial counterexamples are the billiards formed by pairs of confocal conics.

