Some virtually abelian subgroups of the group of analytic symplectic diffeomorphisms of $S^2$

TL;DR

The paper proves that certain subgroups of the group of analytic symplectic diffeomorphisms of the sphere are virtually abelian, especially those with infinite normal solvable subgroups, and establishes a special case of the Tits Alternative.

Contribution

It demonstrates that subgroups with infinite normal solvable parts are virtually abelian and proves a Tits Alternative case for these groups.

Findings

Subgroups with infinite normal solvable subgroups are virtually abelian.

Centralizers of infinite order elements are virtually abelian.

A special case of the Tits Alternative is established for these groups.

Abstract

We show that if $M$ is a compact oriented surface of genus 0 and $G$ is a subgroup of $\Symp^\omega_\mu(M)$ which has an infinite normal solvable subgroup, then $G$ is virtually abelian. In particular the centralizer of an infinite order $f \in \Symp^\omega_\mu(M)$ is virtually abelian. Another immediate corollary is that if $G$ is a solvable subgroup of $\Symp^\omega_\mu(M)$ then $G$ is virtually abelian. We also prove a special case of the Tits Alternative for subgroups of $\Symp^\omega_\mu(S^2).$