Department of Mathematics

Geometry and Topology

  •  Diana Hubbard, University of Michigan
  •  On the braid index and the fractional Dehn twist coefficient
  •  09/14/2017
  •  2:00 PM - 3:00 PM
  •  C304 Wells Hall

The braid index of a knot is the least number of strands necessary to represent the knot as a closure of a braid on that many strands. If we view a braid as an element of the mapping class group of the punctured disk, its fractional Dehn twist coefficient (FDTC) is a number that measures the amount of twisting it exerts about the boundary of the disk. In this talk I will demonstrate that n-braids with FDTC larger than n-1 realize the braid index of their closure. The proof uses the concordance homomorphism Upsilon arising from knot Floer homology as a crucial tool. This is joint work with Peter Feller.



Department of Mathematics
Michigan State University
619 Red Cedar Road
C212 Wells Hall
East Lansing, MI 48824

Phone: (517) 353-0844
Fax: (517) 432-1562

College of Natural Science