Non-abelian free groups admit non-essentially free actions on rooted trees

Abstract

We show that every countable non-abelian free group $Γ$ admits a spherically transitive action on a rooted tree $T$ such that the action of $Γ$ on the boundary of $T$ is not essentially free. This reproves a result of Bergeron and Gaboriau. The existence of such an action answers a question of Grigorchuk, Nekrashevich and Sushchanskii.