Quasi-morphisms on the group of area-preserving diffeomorphisms of the 2-disk via braid groups

Tomohiko Ishida

Recently Gambaudo and Ghys proved that there exist infinitely many quasi-morphisms on the group ${\mathrm{Diff}}_{\Omega }^{\infty }(D^2,\partial D^2)$ of area-preserving diffeomorphisms of the…