Published online by Cambridge University Press: 24 April 2020
We consider dynamical systems $T:X\rightarrow X$ that are extensions of a factor
$S:Y\rightarrow Y$ through a projection
$\unicode[STIX]{x1D70B}:X\rightarrow Y$ with shrinking fibers, that is, such that
$T$ is uniformly continuous along fibers
$\unicode[STIX]{x1D70B}^{-1}(y)$ and the diameter of iterate images of fibers
$T^{n}(\unicode[STIX]{x1D70B}^{-1}(y))$ uniformly go to zero as
$n\rightarrow \infty$ . We prove that every
$S$ -invariant measure
$\check{\unicode[STIX]{x1D707}}$ has a unique
$T$ -invariant lift
$\unicode[STIX]{x1D707}$ , and prove that many properties of
$\check{\unicode[STIX]{x1D707}}$ lift to
$\unicode[STIX]{x1D707}$ : ergodicity, weak and strong mixing, decay of correlations and statistical properties (possibly with weakening in the rates). The basic tool is a variation of the Wasserstein distance, obtained by constraining the optimal transportation paradigm to displacements along the fibers. We extend classical arguments to a general setting, enabling us to translate potentials and observables back and forth between
$X$ and
$Y$ .