The fractional Dehn twist coefficient: from braids to mapping class groups

Diana Hubbard (CUNY)

Abstract: The braid group is a particular example of the mapping class group of a surface with boundary. An invariant that roughly measures how much a mapping class “twists” about the boundary of the surface is the fractional Dehn twist coefficient. In this talk I will discuss some reasons why we care about this invariant, several results about the fractional Dehn twist coefficient for braids, and explore to what extent these results can be extended to more general mapping class groups. This talk will feature joint work with Peter Feller and Hannah Turner.