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Topology Seminar: Justin Lanier (Ga Tech) "Polynomial or not? Twisting rabbits and lifting trees"

Date and time:
Boyd Room 304

Abstract: A polynomial can be viewed as a branched cover of the sphere over itself that is compatible with a complex structure. If handed a topological branched cover of the sphere, we can ask whether it can arise from a polynomial—and if so, which one? In 2006, Bartholdi and Nekrashevych used group theoretic methods to explicitly solve this problem in special cases, including Hubbard’s twisted rabbit problem. We introduce a new topological approach that draws from the theory of mapping class groups of surfaces. By iterating a lifting map on a complex of trees, we are able to certify whether or not a given branched cover arises as a polynomial. This is joint work with Jim Belk, Dan Margalit, and Becca Winarski.

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