33 research outputs found

    The dynamical degree of billiards in an algebraic curve

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    We introduce an algebraic formulation of billiards on plane curves over algebraically closed fields, extending Glutsyuk's complex billiards. For any smooth algebraic curve CC of degree d2d \geq 2, algebraic billiards is a rational (d1)(d-1)-to-(d1)(d-1) surface correspondence on the space of unit cotangent vectors based on CC. We prove that the dynamical degree of the billiards correspondence is at most an explicit cubic algebraic integer ρd<2d2d3\rho_d < 2d^2 - d - 3, depending only on the degree dd of CC. As a corollary, for smooth real algebraic curves, the topological entropy of the classical billiards map is at most logρd\log \rho_d. We further show that the billiards correspondence satisfies the singularity confinement property and preserves a natural 22-form. To prove our bounds, we construct a birational model that partially resolves the indeterminacy of algebraic billiards.Comment: 55 pages; reorganized, detail added, minor changes to theorem statement
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