Ergodic decompositions of geometric measures on Anosov homogeneous spaces

Abstract

Let $G$ be a connected semisimple real algebraic group and $\Gamma$ a Zariski dense Anosov subgroup of $G$ with respect to a minimal parabolic subgroup $P$. Let $N$ be the maximal horospherical subgroup of $G$ given by the unipotent radical of $P$. We describe the $N$-ergodic decompositions of all Burger-Roblin measures as well as the $A$-ergodic decompositions of all Bowen-Margulis-Sullivan measures on $\Gamma\backslash G$. As a consequence, we obtain the following refinement of the main result of [LO]: the space of all {\it non-trivial} $N$-invariant ergodic and $P^\circ$-quasi-invariant Radon measures on $\Gamma\backslash G$, up to constant multiples, is homeomorphic to ${\mathbb R}^{\text{rank}\,G-1}\times \{1, \cdots, k\}$ where $k$ is the number of $P^\circ$-minimal subsets in $\Gamma\backslash G$.