Classification of Conditional Measures Along Certain Invariant One-Dimensional Foliations

Abstract: Let $(M,\mathcal A,\mu)$ be a probability space and $f:M\to M$ a homeomorphism preserving the Borel ergodic probability measure $\mu$. Given $\mathcal F$ a continuous one-dimensional $f$-invariant foliation of $M$ with $C^1$ leaves, we show that if $f$ preserves a continuous $\mathcal{F}$-arc length system, then we only have three possibilities for the conditional measures of $\mu$ along $\mathcal F$, namely: - they are atomic for almost every leaf, or - for almost every leaf their support is a Cantor subset of the leaf or - for almost every leaf they are equivalent to the measure $\lambda_x$ induced by the invariant arc-length system over $\mathcal F$. This trichotomy classifies, for example, the possible disintegrations of ergodic measures along foliations over which $f$ acts as an isometry, and also disintegrations of ergodic measures along the center foliation preserved by transitive partially hyperbolic diffeomorphisms with topological neutral center direction.