Presented By: Topology Seminar - Department of Mathematics
An equator theorem for the 2-sphere
Richard Webb
We will focus on the group of Hamiltonian diffeomorphisms (and/or area-preserving homeomorphisms) of the 2-sphere. A tremendous amount of progress has been made in the study of these groups in the last few years, but many problems remain, including the Equator Conjecture. An equator on the 2-sphere is a simple closed curve whose complementary components have equal area. The Equator Conjecture predicts that for any positive K, there are pairs of equators such that any Hamiltonian diffeomorphism sending one equator to the other must have Hofer norm larger than K. We will prove an alternative conjecture, where we replace “Hofer norm” with “quantitative fragmentation norm”. To prove this, we construct new quasimorphisms defined on the group of area-preserving homeomorphisms of the 2-sphere, coming from methods inspired from mapping class groups and geometric group theory. Joint work with Yongsheng Jia.
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