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Laurent Bartholdi: Insanely twisted rabbits

Laurent Bartholdi, Georg-August University of Göttingen, Germany

Time: Wed 2009-11-18 16.00

Location: Room 3721, department of mathematics, KTH, Lindstedtsvägen 25, 7th floor

(Topological) branched coverings of the sphere, modulo a natural ("isotopy") relation, are interesting combinatorial objects; and a result by Thurston explains, at least theoretically, when such a covering is equivalent to a rational map. I will explain how such coverings can be conveniently encoded in group theory, and how that language can be used to answer a long-standing open problem by Douady and Hubbard, the "Twisted rabbit problem". I will then discuss visualizations of "matings" of polynomials (the topological branched covering obtained from gluing together two polynomials at infinity) through the same method. This is joint work with Volodya Nekrashevych.

Coffee and tea is served at 3:30 in the lunch room.

Title Date
Sandra Di Rocco: Interaction between Convex and Algebraic Geometry Dec 16, 2009
Alexander Gorodnik: Arithmetic Geometry and Dynamical Systems Nov 18, 2009
Laurent Bartholdi: Insanely twisted rabbits Nov 18, 2009
Nils Dencker: The spectral instability of differential operators Nov 04, 2009
Peter Jagers: Extinction: how often, how soon, and in what way? Oct 21, 2009
Norbert Peyerimhoff: Expander graphs — some background and new examples Oct 07, 2009
Saharon Shelah: Hilbert's First Problem and the number four Sep 23, 2009
Jürg Kramer: Irrationality of √2 and Arakelov Geometry Sep 09, 2009