Nielsen realization for sphere twists on 3-manifolds
摘要
For a 3-manifold M, the twist group Twist(M) is the subgroup of the mapping class group Mod(M) generated by twists about embedded 2-spheres. We study the Nielsen realization problem for subgroups of Twist(M). We prove that a nontrivial subgroup G < Twist(M) is realized by diffeomorphisms if and only if G is cyclic and M is a connected sum of lens spaces, including S1 × S2. We also apply our methods to the Burnside problem for 3-manifolds and show that Diff(M) does not contain an infinite torsion group when M is reducible and not a connected sum of lens spaces.