Ulrike Tillmann (Oxford University)
tillmann@maths.ox.ac.uk The Dehn twist of two curves on an oriented surface that intersect once satisfy the braid relations. This gives rise to a natural map from the braid groups to the mapping class groups. I will identify this map stably and thus prove an old conjecture of Harer on image of this map in homology. The main tool is categorical delooping. This work is joint work with Yongjin Song.