Representations of some lattices into the group of analytic diffeomorphisms of the sphere ${\mathbb{S}}^2$

Abstract

In \cite{Ghys} it is proved that any morphism from a subgroup of finite index of $\mathrm{SL}(n,\mathbb{Z})$ to the group of analytic diffeomorphisms of ${\mathbb{S}}^2$ has a finite image as soon as $n\ge 5$. The case $n=4$ is also claimed to follow along the same arguments; in fact this is not straightforward and this case indeed needs a modification of the argument. In this paper we recall the strategy for $n\ge 5$ and then focus on the case $n=4$.