Addendum to: Commensurations of the Johnson kernel

Abstract

Let K(S) be the subgroup of the extended mapping class group, Mod(S), generated by Dehn twists about separating curves. In our earlier paper, we showed that Comm(K(S)) and Aut(K(S)) are both isomorphic to Mod(S) when S is a closed, connected, orientable surface of genus g at least 4. By modifying our original proof, we show that the same result holds for g at leat 3, thus confirming Farb's conjecture in all cases (the statement is not true for any g less than 3).

4 pages, 2 figures; to appear in Geometry and Topology

References in corpus (1)

• Automorphisms of Torelli groups

Cited by in corpus (7)

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• Commensurators of surface braid groups
• The co-Hopfian property of surface braid groups
• Injective Simplicial Maps of the Arc Complex on Nonorientable Surfaces