Primitive-stable representations of the free group

Automorphisms of the free group $F_n$ act on its representations into a given group $G$. When $G$ is a compact Lie group and $n>2$, Gelander showed that this action is ergodic. We consider the case $G=PSL(2,{\bf C})$, where the variety of (conjugacy classes of) representations has a natural invariant decomposition, up to sets of measure 0, into {\it discrete} and {\it dense} representations. This turns out {\it not} to be the relevant decomposition for the dynamics of the outer automorphism group. Instead we describe a set called the {\it primitive-stable} representations containing discrete as well as dense representations, on which the action is properly discontinuous.