Extensions of probability-preserving systems by measurably-varying homogeneous spaces and applications

Tim Austin. "Extensions of probability-preserving systems by measurably-varying homogeneous spaces and applications." Fundamenta Mathematicae 210.2 (2010): 133-206. <http://eudml.org/doc/282609>.

@article{TimAustin2010,
abstract = {We study a generalized notion of a homogeneous skew-product extension of a probability-preserving system in which the homogeneous space fibres are allowed to vary over the ergodic decomposition of the base. The construction of such extensions rests on a simple notion of 'direct integral' for a 'measurable family' of homogeneous spaces, which has a number of precedents in older literature. The main contribution of the present paper is the systematic development of a formalism for handling such extensions, including non-ergodic versions of the results of Mackey describing ergodic components of such extensions, of the Furstenberg-Zimmer structure theory and of results of Mentzen describing the structure of automorphisms of such extensions when they are relatively ergodic. We then offer applications to two structural results for actions of several commuting transformations: firstly to describing the possible joint distributions of three isotropy factors corresponding to three commuting transformations; and secondly to describing the characteristic factors for a system of double non-conventional ergodic averages. Although both applications are modest in themselves, we hope that they point towards a broader usefulness of this formalism in ergodic theory.},
author = {Tim Austin},
journal = {Fundamenta Mathematicae},
keywords = {Probability-preserving system; skew product; isometric extension; ergodic decomposition; Mackey theory; Furstenberg-Zimmer theory},
language = {eng},
number = {2},
pages = {133-206},
title = {Extensions of probability-preserving systems by measurably-varying homogeneous spaces and applications},
url = {http://eudml.org/doc/282609},
volume = {210},
year = {2010},
}

TY - JOUR
AU - Tim Austin
TI - Extensions of probability-preserving systems by measurably-varying homogeneous spaces and applications
JO - Fundamenta Mathematicae
PY - 2010
VL - 210
IS - 2
SP - 133
EP - 206
AB - We study a generalized notion of a homogeneous skew-product extension of a probability-preserving system in which the homogeneous space fibres are allowed to vary over the ergodic decomposition of the base. The construction of such extensions rests on a simple notion of 'direct integral' for a 'measurable family' of homogeneous spaces, which has a number of precedents in older literature. The main contribution of the present paper is the systematic development of a formalism for handling such extensions, including non-ergodic versions of the results of Mackey describing ergodic components of such extensions, of the Furstenberg-Zimmer structure theory and of results of Mentzen describing the structure of automorphisms of such extensions when they are relatively ergodic. We then offer applications to two structural results for actions of several commuting transformations: firstly to describing the possible joint distributions of three isotropy factors corresponding to three commuting transformations; and secondly to describing the characteristic factors for a system of double non-conventional ergodic averages. Although both applications are modest in themselves, we hope that they point towards a broader usefulness of this formalism in ergodic theory.
LA - eng
KW - Probability-preserving system; skew product; isometric extension; ergodic decomposition; Mackey theory; Furstenberg-Zimmer theory
UR - http://eudml.org/doc/282609
ER -