UW-Milwaukee Department of Mathematical Sciences presents,

Dr. Becca Winarski;
Visiting Assistant Professor of Mathematical Sciences
UW-Milwaukee

Friday, September 16, 2016
2:00pm in EMS E495

*Refreshments will be served at 1:30pm in EMS E424A*
Title:
Lifting Homeomorphisms of the Sphere
Description/Abstract:
Birman and Hilden ask: given finite branched cover X over the 2-sphere, does every homeomorphism of the sphere lift to a homeomorphism of X? For covers of degree 2, the answer is yes, but the answer is sometimes yes and sometimes no for higher degree covers. In joint work with Ghaswala, we completely answer the question for cyclic branched covers. When the answer is yes, there is an embedding of the mapping class group of the sphere into a finite quotient of the mapping class group of X. In a family where the answer is no, we find a presentation for the group of isotopy classes of homeomorphisms of the sphere that do lift, which is a finite index subgroup of the mapping class group of the sphere.