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.

Kollokvier 2009

Titel Datum
Sandra Di Rocco: Interaction between Convex and Algebraic Geometry 2009‑12‑16
Alexander Gorodnik: Arithmetic Geometry and Dynamical Systems 2009‑11‑18
Laurent Bartholdi: Insanely twisted rabbits 2009‑11‑18
Nils Dencker: The spectral instability of differential operators 2009‑11‑04
Peter Jagers: Extinction: how often, how soon, and in what way? 2009‑10‑21
Norbert Peyerimhoff: Expander graphs — some background and new examples 2009‑10‑07
Saharon Shelah: Hilbert's First Problem and the number four 2009‑09‑23
Jürg Kramer: Irrationality of √2 and Arakelov Geometry 2009‑09‑09